-
Topic 2 Mechanics
2.1 Kinematics
2.1.1 Define displacement, velocity, speed and acceleration.
Displacement- Defined as the change in position of an object.
Displacement is a
quantity that has both direction and magnitude, it is a
vector.
Measured in metres.
Speed- How far an object travels in a given time.
Rate of change of distance (ms-1)
Velocity- The vector version of speed. Tells us the magnitude of
how fast an
object is moving and the direction in which it is moving.
(ms-1)
dTimeElapse
ntDisplacemeocityAverageVel =
Acceleration- Rate of change of velocity (ms-2)
dTimeElapse
locityChangeInVeelerationAverageAcc =
2.1.2 Explain the difference between instantaneous and
average
values of speed, velocity and acceleration. Instantaneous values
of velocity speed and acceleration are taken at a particular
moment. In
any realistic situation they will be constantly varying and is
not always meaningful or useful
to know this e.g. drivers need to keep their instantaneous speed
below the speed limit.
Average velocity, speed and acceleration are taken over a
certain period of time or distance.
E.g. Average speed between Porto and Lisbon = distance/time =
350/km/3 hours 30 min =
100 kmh-1
2.1.3 Outline the conditions under which the equations for
uniformly
accelerated motion may be applied. The following equations of
motion may be applied to an object that has a constant
acceleration.
t
uva
)( =
2
21 atuts +=
asuv 222 +=
v= final velocity/ ms-1)
u= initial velocity / ms-1
a= acceleration/ ms-2
s= displacement/m
t=time/s
2.1.4 Identify the acceleration of a body falling in a vacuum
near the
Earths surface with the acceleration g of free fall.
-
Free fall is the uniform acceleration (ignoring the effect of
air resistance) in the vertical
direction of an object in a uniform gravitational field. All
falling objects have the same
acceleration independent of their masses. On earth all objects
accelerate towards the
ground at 9.81 ms-2.
Acceleration due to gravity can be measured in a number of
ways. In the arrangement that is shown a timer starts when
the ball is released form an electromagnet and stops when
the ball passes through a gate at the bottom. The acceleration
due to gravity can then be calculated using:
2
2
t
sg =
Acceleration due to gravity can also be calculated using light
gates of ticker timers.
2.1.5 Solve problems involving the equations of uniformly
accelerated motion.
This question is about throwing a stone from a cliff.
Antonia stands at the edge of a vertical cliff and throws a
stone vertically
upwards.
Sea
v = 8.0ms 1
The stone leaves Antonias hand with a speed v = 8.0ms1
.
The acceleration of free fall g is 10 m s2
and all distance measurements are
taken from the point where the stone leaves Antonias hand.
(a) Ignoring air resistance calculate
(i) the maximum height reached by the stone.
asuv 222 +=
s
vs
2
2
=
-
102
82
=s
ms 2.3=
(2)
(ii) the time taken by the stone to reach its maximum
height.
t
uva
=
a
uvt
=
10
8=t
st 8.0=
(1)
The time between the stone leaving Antonias hand and hitting the
sea is 3.0 s.
(b) Determine the height of the cliff.
Time to go form top of cliff to sea = 3.0 (2 x 0.8) = 1.4s
2
21 atuts +=
)4.110()4.10.8( 221
+=s
(3)
(Total 6 marks)
2.1.6 Describe the effects of air resistance on falling
objects.
Air resistance acts upon all moving objects. As the velocity of
an object increases the size of
the air resistance also increases.
Eventually the force of air resistance will equal the force of
gravity. When this happens the
object will stop accelerating. It has reached its terminal
velocity.
ms 21=
-
The terminal velocity of an object is dependant on its shape. A
feather has a lower terminal
velocity than a hammer.
2.1.7 Draw and analyse distancetime graphs, displacementtime
graphs, velocitytime graphs and accelerationtime graphs.
Displacement time graphs
0
2
4
6
8
10
12
0 2 4 6 8 10 12
time /s
dispalcement / m
The gradient of a displacement - time graph is the velocity.
Object travels at a constant speed for the first five
seconds
The object then
is stationary for three seconds.
The object returns to
its original location at a faster speed.
-
Velocity time graphs
The gradient of a velocity time graph tells the acceleration of
the object. If the line is flat
the object is travelling at a constant velocity.
The area under the graph represents the distance travelled.
Acceleration time graphs
The area under an acceleration time graph represents the change
in velocity.
2.1.8 Calculate and interpret the gradients of displacementtime
graphs and velocitytime graphs, and the areas under
velocitytime
graphs and accelerationtime graphs.
1) The graph shows the variation with time t of the velocity v
of an object.
v
t
Which one of the following graphs best represents the variation
with time t of the
acceleration a of the object?
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15
time /s
velocity / m/s
The objects velocity is increasing
The object is slowing down.
-
0 0
0 0
0 0
0 0
a a
a a
t t
t t
A. B.
C. D.
2) An athlete runs round a circular track at constant speed.
Which one of the following
graphs best represents the variation with time t of the
magnitude d of the
displacement of the athlete from the starting position during
one lap of the track?
d
d
d
d
0
0
0
0
0
0
0
0
t
t
t
t
A.
C.
B.
D.
-
2.1.9 Determine relative velocity in one and in two
dimensions.
Frames of Reference: If two things are moving in the same
straight line but are travelling at
different speeds, then we can work out their relative velocities
by simple addition or
subtraction as appropriate. For example, imagine two cars
travelling along a straight road at
different speeds. If one car (travelling at 30 m/s) overtakes
the other car (travelling at 25
m/s), then according to the driver of the slow car, the relative
velocity of the fast car is 5
m/s. In technical terms what we are doing is moving from one
frame of reference into
another. The velocities of 25 m/s and 30 m/s were measured
according to a stationary
observer on the side of the road. We moved from this frame of
reference into the drivers
frame of reference.
-
2.2 Force and Dynamics
2.2.1 Calculate the weight of a body using the expression W =
mg.
The term weight can mean different things to Physics. Some
define it as the gravitational
force acting on a mass, other define it as the reading on a
supporting scale. Weight is a
force and as the strength of gravity varies depending on where
you are the weight of an
object will also vary.
rengthnalFieldStGravitatiomassWeight =
The mass of an object is a single quantity but has tow different
properties Gravitational
Mass and Inertial Mass.
The inertial mass of an object determines how that object will
respond to a given force. The
gravitational mass of an object tells us how much gravitational
force that an object will feel
when it is near another object.
Although the two quantities are different they turn out to be
equivalent. The fact that all
objects accelerate at the same rate shows this.
2.2.2 Identify the forces acting on an object and draw free-body
diagrams representing the forces acting.
Free body diagrams show the size and direction all of the forces
acting on an object.
A simple situation is a bag resting on a table.
Free body diagram for the shopping Free body diagram for the
table
Gravity is pulling the bag downwards and
the reaction from the table is pushing the
bag up.
2.2.3 Determine the resultant force in different situations. It
is unusual for only one force to be acting on an object. Usually we
have to add the forces
together to calculate the resultant force.
-
If the forces are acting in one dimension then they can be
simply added together as shown
below.
If the forces are not in the same dimension then the resultant
force can be drawn onto a
scale diagram. Force F1 has been moves so that it is nose to
tail with F2. The resultant
force can then be drawn onto the diagram showing its magnitude
and direction.
2.2.4 State Newtons first law of motion. Every body perseveres
in its state of being at rest or of moving uniformly straight
forward,
except insofar as it is compelled to change its state by force
impressed.
"A particle will stay at rest or continue at a constant velocity
unless acted upon by an
external unbalanced net force."
2.2.5 Describe examples of Newtons first law. When a car moves
at a steady speed all forces acting on it are balanced.
2.2.6 State the condition for translational equilibrium. The
change of momentum of a body is proportional to the impulse
impressed on the body,
and happens along the straight line on which that impulse is
impressed.
-
2.2.7 Solve problems involving translational equilibrium.
2.2.8 State Newtons second law of motion.
2.2.9 Solve problems involving Newtons second law.
2.2.10 Define linear momentum and impulse.
Linear momentum is defined as the product of mass and
velocity.
P=mv where p= linear momentum/ kgms-1 m= mass/Kg v= velocity/
ms-1
Impulse is the product of Force and time
I= Ft I= impulse/Ns F= Force/N t=time/s
It can be shown that linear momentum and impulse have the same
units.
Ns = Kgms-2s
Ns = Kgms-1
So impulse and momentum are the same quantity.
In other words:
Impulse = change in linear momentum.
This is very useful for calculations.
Force/time graphs The area under a force-time graph is the
impulse.
2.2.11 Determine the impulse due to a time-varying force by
interpreting a forcetime graph.
2.2.12 State the law of conservation of linear momentum.
In a closed system the fatal linear momentum is constant
e.g. Total momentum before a collision = Total momentum after a
collision
or Total momentum after an explosion = 0
2.2.13 Solve problems involving momentum and impulse.
2.2.14 State Newtons third law of motion. For a force there is
always an equal and opposite reaction: or the forces of two bodies
on
each other are always equal and are directed in opposite
directions.
When two bodies A and B interact, the force that A exerts on B
is equal and opposite to the
force that exerts on A.
2.2.15 Discuss examples of Newtons third law.
-
If one roller-skater pushes another, they both feel a force. The
forces must be equal and
opposite, but the acceleration will be different.
A book exerting a force of 10N in a table the table will also
exert 10N back.
-
2.3 Work, energy and power
2.3.1 Outline what is meant by work.
Work is what is accomplished when a force acts on an object as
the object moves through a
distance.
Work is a form of energy and is measured in joules.
2.3.2 Determine the work done by a non-constant force by
interpreting a forcedisplacement graph.
As work is the product of force and distance, it can be
represented as the area under a
graph of force as a function of distance. In the below graph the
shaded region represents
the work done on an object that undergoes a constant force.
Thus, the work done (area of the shaded region) can be calculated
by multiplying distance (base) by force (height).
This graphical method of calculating work is also useful in
estimating the work that results
from a varying force. The force applied to the object in changes
over time.
The work done cannot be calculated by finding the area of a
simple rectangle but it can be
estimated by dividing the area into small segments, calculating
the area of each segment, and adding all of the segment areas.
Work Done = Force x Distance
W=Fs
-
Such areas are often divided into rectangles because the area of
a rectangle is easily
calculated. However, triangles, trapezoids, or any type of
segments may be used. The better the segments fit the area, the
more precise the estimate.
2.3.3 Solve problems involving the work done by a force.
The diagram below shows the variation with displacement x of the
force F acting on an
object in the direction of the displacement.
F
xxx
P
Q
R
S
TVW
2100
Which area represents the work done by the force when the
displacement changes from x1 to x2?
A. QRS
B. WPRT
C. WPQV
D. VQRT
2.3.4 Outline what is meant by kinetic energy. Kinetic Energy:
The energy of a moving body because of its movement.
The unit of Kinetic Energy is the joules /J.
K.E. = mv2
-
2.3.5 Outline what is meant by change in gravitational
potential
energy. Gravitational potential energy is energy that is stored
in an object by its height.
The unit of gravitational potential energy is the joule /J.
2.3.6 State the principle of conservation of energy.
Energy is conserved; this means that the total amount of energy
in the universe is constant.
Energy cannot be made or destroyed. It can be transformed from
one form to another.
2.3.7 List different forms of energy and describe examples of
the
transformation of energy from one form to another. Kinetic
Energy Electrostatic Potential Chemical energy Radiant energy
Gravitational Potential Thermal Energy Nuclear energy Solar
energy
Elastic Potential Energy Electrical Energy Internal Energy Light
energy
Situation Energy Conversion Formula
Brakes get hot K.E. - Thermal Energy mv2 = mcT
Car going up hill K.E. - GPE mv2 = mgh
Stone falling GPE K.E. mgh = mv2
2.3.8 Distinguish between elastic and inelastic collisions. Most
collisions are inelastic because kinetic energy is transferred to
other forms of energy
such as thermal energy, potential energy, and soundduring the
collision process. If you are
asked to determine if a collision is elastic or inelastic,
calculate the kinetic energy of the
bodies before and after the collision. If kinetic energy is not
conserved, then the collision is
inelastic. Momentum is conserved in all inelastic
collisions.
G.P.E = mgh
-
An elastic collision is a collision where no mechanical energy
is lost. The collision of pool
balls is a good example of an elastic collision. Although some
energy is lost (as sound
energy) this is a small fraction of the total energy.
For elastic collisions the relative velocity before is always
equal to the relative velocity after
the collision.
Particles in an ideal gas collide elastically.
2.3.9 Define power. Power is the rate of doing work or
transferring energy.
The unit of power is the Watt (W). 1 watt is equivalent to 1
Joule of energy being
transformed per second.
2.3.10 Define and apply the concept of efficiency.
In any energy transfer some of the work is transferred into a
form that is not useful. This
energy is wasted. Efficiency is defined as the ratio of the
useful energy to the total energy
transferred.
Efficiency does not have any units and is usually expressed as a
percentage.
2.3.11 Solve problems involving momentum, work, energy and
power.
yInTotalEnerg
gyOutUsefulEnerEfficiency =
time
WorkDonePower =
-
1) This question is about projectile motion and the use of an
energy argument to find
the speed with which a thrown stone lands in the sea.
Christina stands close to the edge of a vertical cliff and
throws a stone. The diagram
below (not drawn to scale) shows part of the trajectory of the
stone. Air resistance is
negligible.
Point P on the diagram is the highest point reached by the stone
and point Q is at
the same height above sea level as point O.
(a) At point P on the diagram above draw arrows to represent
(i) the acceleration of the stone (label this A).
(1)
(ii) the velocity of the stone (label this V).
(1)
The stone leaves Christinas hand (point O) at a speed of 15 m
s1
in the
direction shown. Her hand is at a height of 25 m above sea
level. The mass of the
stone is 160 g. The acceleration due to gravity g = 10 m s2
.
(b) (i) Calculate the kinetic energy of the stone immediately
after it leaves
Christinas hand.
KE = 21 mv
2
= 0.08 225
= 18 J
(1)
(ii) State the value of the kinetic energy at point Q.
18 J
(1)
-
(iii) Calculate the loss in potential energy of the stone in
falling from point
Q to hitting the sea.
loss in PE = mgh
= 25 x 10 x 0.16
= 40J
(1)
(iv) Determine the speed with which the stone hits the sea.
Total KE = 40J + 18J = 56J
2
21 mvKE =
m
KEv
2=
16.0
562=v
127 = msv
(2)
(Total 7 marks)
-
2.4 Uniform circular motion
2.4.1 Draw a vector diagram to illustrate that the acceleration
of a
particle moving with constant speed in a circle is directed
towards the centre of the circle.
Objects perform uniform circulation motion when acted upon by a
force towards the centre
of the motion ( centripetal force) e.g.
The only force on the Moon in its orbit is the pull of the
Earth, which supplies the centripetal
force.
2.4.2 Apply the expression for centripetal acceleration.
2.4.3 Identify the force producing circular motion in
various
situations.
2.4.4 Solve problems involving circular motion.
-
Allan Riddick
Topic 3.1 Thermal concepts 3.1.1 State that temperature
determines the direction of thermal energy transfer between two
objects. Temperature determines the direction of heat transfer.
Heat always travels from hot to cold. When two objects are in
contact with each other and at the same temperature, we say they
are in thermal equilibrium. 3.1.2 State the relation between the
Kelvin and Celsius scales of temperature.
There are two temperature scales that can be used, the Kelvin
scale and the Celsius scale. The relationship between then is
0C is the melting point of pure ice. 0K is the absolute zero,
the coldest temperature possible. At 0k, the particles have no
kinetic energy, it is practically and theoretically impossible to
reach 0K but we can get close.
0K is - 273.16C The coldest temperature ever recorded was
700nK
3.1.3 State that the internal energy of a substance is the total
potential energy and random
kinetic energy of the molecules of the substance.
The internal energy of a system is more commonly referred to as
the Thermal Energy. Internal energy is the sum of kinetic and
potential energy of the particles of a substance. The potential
energy is due the energy stored in the bonds (bond energy) and the
intermolecular force of attraction between particles. The kinetic
energy is due to the translational, vibrational and rotational
motion of the particles.
T (K) = t (C) + 273
-
Allan Riddick
When you heat a substance, the particles more faster (increase
KE.) and the bonds stretch (increase PE.) 3.1.4 Explain and
distinguish between the macroscopic concepts of temperature,
internal energy
and thermal energy (heat)
Temperature is a measure of the hotness of something. In
practice the temperature determines the direction of thermal energy
transfer between a body at a higher temperature to a body at a
lower temperature. At a microscopic level temperature is a measure
of the average kinetic energy per molecule. The internal energy is
sum total of the energy of all of the molecules in an object. The
terms internal energy and thermal energy can be used
interchangeably. 3.1.5 Define the mole and molar mass. The mole is
the SI unit for the amount of a substance. The molar mass is the
mass of one mole of a substance. 3.1.6 Define the Avogadro
constant.
1 mole of a substance contains Avogadros number (6.02 x1023) of
molecules 12g of carbon-12 contains 6.02 x1023 atoms.
-
Allan Riddick
3.2 Thermal properties of matter 3.2.1 Define specific heat
capacity and thermal capacity. Specific Heat Capacity is the amount
of energy required to heat 1kg of a substance by 1C or 1K.
Thermal Capacity is amount of energy needed to change
temperature of an object by 1C or 1K. 3.2.2 Solve problems
involving specific heat capacities and thermal capacities.
3.2.3 Explain the physical differences between the solid, liquid
and gaseous phases in terms of
molecular structure and particle motion.
A solid is made up of particles that are arranged in a solid 3D
shape. There is a strong force of attraction between the particles.
If the solid was to be heated the particles would gain energy and
start to vibrate more vigorously.
In a liquid the particles are free to move around. A liquid will
mould itself to the shape of the container that it is in. There is
still a force of attraction between the particles.
In a gas the particles are free to move around. The particles
have a lot of energy so move quickly. Collisions between the
molecules and the side of the container are responsible for the
pressure which a gas exerts. There is almost no force of attraction
between the molecules in a gas.
3.2.4 Describe and explain the process of phase changes in terms
of molecular behaviour.
Q = cmT
Where Q = Change in Heat Energy (J) c = Specific Heat Capacity
(Jkg-1K-1) m = Mass (kg)
T =Change in temperature(K)
-
Allan Riddick
Kinetic theory can be used to explain what happens to a
substance as it is heated. To change form a solid to a liquid the
particles must gain sufficient kinetic energy to overcome the
forces between them and break away from their fixed positions.
While the substance is changing state its temperature does not
increase. This can be seen as a plateau (BC) when you look at a
heating curve.
Once the phase change has been completed the particles begin to
gain more kinetic energy and the temperature of the substance again
increases.
As the boiling point is increased the particles gain enough
energy to completely overcome the intermolecular forces and escape
into the gaseous state. As this happens there is another plateau in
the cooling curve (D-E).
Condensation: In condensation the particles are slowing
themselves down becoming closer together and so forming water.
Evaporation: The particles are heated together, they gain kinetic
energy and when they gain enough energy they escape. Freezing: The
particles lose kinetic energy and form a solid 3.2.5 Explain in
terms of molecular behaviour why temperature does not change during
a phase
change.
The energy is being used to break or make bonds and so the
energy is not turned into kinetic energy.
-
Allan Riddick
3.2.6 Distinguish between evaporation and boiling.
Evaporation is the change of state from liquid to gas that
occurs below the boiling point of that liquid. In a liquid a small
amount of the molecules have sufficient kinetic energy to leave the
surface of the liquid and become a gas. As the high energy
molecules are leaving the liquid the temperature of the remaining
liquid falls. The rate of evaporation depends on:
The surface area of the liquid. As molecules only leave from the
surface of the liquid, if there is a large surface area then
evaporation will occur more quickly.
The temperature of the liquid. If the liquid is warmer then more
molecules will have sufficient Kinetic energy to escape.
The pressure of the air above the liquid. If the pressure is
higher more Kinetic Energy will be required to escape.
Movement of air. If there is a draught across the liquid the
rate of evaporation will increase. Boiling occurs when the whole
liquid is heated to its boiling point. All the molecules have
sufficient Kinetic Energy to turn into a gas. 3.2.7 Define specific
latent heat.
Latent heat of Vaporisation is the heat required to vaporise a
unit of mass. Vaporisation is the technical term for the change in
state between a liquid and a gas. 3.2.8 Solve problems involving
specific latent heats. 3.2.9 Define pressure. Pressure is the force
exerted per unit area. How is pressure exerted by a gas: Particles
bounce off the walls of a container as they bounce their momentum
changes. Momentum change/ time = Force Pressure = Force/ Area so
pressure is exerted 3.2.10 State the assumptions of the kinetic
model of an ideal gas.
Kinetic theory uses the model of small particles bouncing around
to describe the properties of gases (mainly) and matter in
general.
Matter consists of large numbers of tiny particles Particles are
in constant motion moving in straight lines and thus have kinetic
energy. All collisions between particles and the sides of the
container are elastic. There are no forces between the particles of
attraction or repulsion. The average kinetic energy per particle is
proportional to the Kelvin temperature of the gas.
3.2.11 State that temperature is a measure of the average random
kinetic energy of the molecules
of an ideal gas. Temperature is a measure of the average kinetic
energy per particles of an ideal gas. 3.2.12 Explain the
macroscopic behaviour of an ideal gas in terms of a molecular
model.
Boyles Law:
-
Allan Riddick
Boyle's law states that at a constant temperature the volume of
a gas increases when the pressure decreases. This is because the
particles dont lose kinetic energy and they collide more frequently
against the walls.
Charles Law: At constant pressure, the volume of a given mass of
an ideal gas increases or decreases by the same factor as its
temperature (in Kelvin) increases or decreases. This is because as
temperature increases particles gain more kinetic energy which
causes pressure to increase, hence volume increases as collisions
increase.
Pressure Law: As temperature increases so does pressure this is
because an increase in temperature the atoms will move faster and
so they will collide more often the walls of a container and thus
increasing the pressure.
2
2
1
1
Tp
Tp
=
or
.constTp
=
2
2
1
1
TV
TV
=
or
.constTV
=
p1V1 = p2V2
or
pV = constant
-
Allan Riddick
4.1 Kinematics of simple harmonic motion (SHM) 4.1.1 Describe
examples of oscillations. Examples of Simple Harmonic Motion
include:
1. Simple spring oscillator
2. Pendulum for small angles of oscillation
4.1.2 Define the terms displacement, amplitude, frequency,
period and phase difference. Displacement Distance from the
equilibrium point
Amplitude The maximum value for displacement from the mid
point.
Frequency (f): The number of oscillations per second measured in
hertz (Hz) 1 Hz = 1 oscillation
per second.
Period (T): The time taken for one oscillation measured in
seconds.
fT1
=
Phase difference A way of comparing two oscillations by finding
the difference between their
phases.
The two waves shown have a phase difference of 180.
This means that the first wave is half a wavelength in
front of the second one.
4.1.3 Define simple harmonic motion (SHM) and state the defining
equation as a = 2x.
For an oscillation to be described as Simple Harmonic:
the force or acceleration is always directed to the centre of
the motion.
the force or acceleration is proportional to the distance from
the centre of motion 4.1.4 Solve problems using the defining
equation for SHM. 4.1.5 Apply the equations v = v0 sin t, v = v0
cos t , v =(x0
2 x2) , x = x0 cos t and x = x0 sin t as solutions to the
defining equation for SHM. 4.1.6 Solve problems, both graphically
and by calculation, for acceleration, velocity and displacement
during SHM.
-
Allan Riddick
4.2 Energy changes during simple harmonic motion (SHM) 4.2.1
Describe the interchange between kinetic energy and potential
energy during SHM.
4.2.2 Apply the expressions EK= m
2(x02 x2) for the kinetic energy of a particle
undergoing SHM, ET= m2x0
2 for the total energy and EP= m2x2 for the potential
energy.
4.2.3 Solve problems, both graphically and by calculation,
involving energy changes during SHM.
-
Allan Riddick
4.3 Forced oscillations and resonance 4.3.1 State what is meant
by damping. Damping is a force that is always in the opposite
direction to the direction of motion of the oscillating
particle and that the force is a dissipative force. 4.3.2
Describe examples of damped oscillations. This happens on cars in
their suspensions, when it vibrates the damper tries to reduce the
number of
oscillations, to reduce the possible effects. On a piano the
pedals reduce the oscillations of the springs
of the piano. One pedal reduces the damping and one cuts
completely the oscillations.
4.3.3 State what is meant by natural frequency of vibration and
forced oscillations. The natural frequency is the frequency that an
object will oscillate at if it if moved from its equilibrium
position and released. When a guitar string of a certain length
is plucked it vibrates at a certain
frequency.
Objects can also be made to oscillate by an external force. This
is known as forced oscillation.
4.3.4 Describe graphically the variation with forced frequency
of the amplitude of vibration of an object close to its natural
frequency of vibration.
4.3.5 State what is meant by resonance. If an object is forced
to oscillate at its natural frequency resonance will occur.
Resonance results in
oscillations of a very large amplitude.
4.3.6 Describe examples of resonance where the effect is useful
and where it should be avoided. Resonance can be a serious problem.
When designing an aeroplane wing care must be taken that it
will not resonate in flight.
-
Allan Riddick
4.4 Wave characteristics 4.4.1 Describe a wave pulse and a
continuous progressive (travelling) wave. 4.4.2 State that
progressive (travelling) waves transfer energy. Waves transfer
energy with no net movement in the medium they travel through.
4.4.3 Describe and give examples of transverse and of longitudinal
waves.
Above is a diagram of a transversal wave. Transverse waves can
be defined by the fact that they
oscillate at right angles to the direction of energy transfer.
Examples of such waves are ripples in the
water of a pond, and vibrations along a taught rope.
Above is a diagram of a longitudinal wave. Examples of such
waves are sound waves and compression
waves down a spring. Note that these waves do not oscillate
perpendicular to the ray or direction of
energy transfer.
4.4.4 Describe waves in two dimensions, including the concepts
of wavefronts and of rays. There are some important aspects of all
waves which can be studied using the above.
Wave fronts These are the movement of the wave pattern, i.e.
when the curve is going up, or
going down. The wave fronts highlight the parts of the waves
which are moving together.
Rays the rays highlight general direction of the wave and
therefore the direction of the energy
transfer.
4.4.5 Describe the terms crest, trough, compression and
rarefaction. In the above we have seen various terms to describe
features of waves, and below is a definition for
these:
Crest This is the highest point the wave oscillates, it is the
top of the wave. This is a feature
of a transversal wave.
Trough The trough is the lowest point to which the wave
oscillates, in other words it is the
bottom of the wave. Again this is only a feature of transversal
waves.
Compressions This is the point in a longitudinal wave where
everything is bunched together,
i.e. there is high pressure.
Rarefacations This is the point where all the points are far
apart and there is low pressure.
-
Allan Riddick
4.4.6 Define the terms displacement, amplitude, frequency,
period, wavelength, wave speed and intensity. Amplitude The
amplitude is a measure of the maximum displacement of the wave. If
there is no
energy loss this value is constant.
Period This is the time taken for one complete oscillation in
seconds; this is also referred to as
the periodic time.
Frequency This is the number of oscillations that take place in
one second, this is measured in
hertz. 10Hz would mean that a wave is oscillating 10 times a
second.
Wavelength This is the shortest distance between one oscillation
this can be the distance between
any two points as long as the two points are in the same
position.
Wavespeed This is the speed (in ms-1) at which the oscillation
pass a stationary point.
Intensity The intensity is the power per unit area that is
absorbed by the observer. In English this
is the power that the wave carries per oscillation to say as
such, and is proportional to
the square of the amplitude.
4.4.7 Draw and explain displacementtime graphs and
displacementposition graphs for transverse and for longitudinal
waves.
4.4.8 Derive and apply the relationship between wave speed,
wavelength and frequency.
4.4.9 State that all electromagnetic waves travel with the same
speed in free space, and recall the orders of magnitude of the
wavelengths of the principal radiations in the electromagnetic
spectrum.
Wave Speed (ms-1) = Frequency (Hz) x wavelength (m)
v = f
-
Allan Riddick
-
Allan Riddick
4.5 Wave properties 4.5.1 Describe the reflection and
transmission of waves at a boundary between two media. At a
boundary between two media, two things happen:
Reflection: In this case the law of reflection applies incident
angle = reflected angle when
measured from the normal ( an imaginary line at right angles to
the surface).
Refraction: In this case the wave is refracted towards the
normal entering a slower medium and
away from the normal entering faster medium.
4.5.2 State and apply Snells law. 4.5.3 Explain and discuss
qualitatively the diffraction of waves at apertures and obstacles.
Diffraction is when the wave spreads out after passing through a
narrow opening.
In general, diffraction is greatest when the size of the opening
is of the same order as the wavelength.
4.5.4 Describe examples of diffraction.
Waves in the harbour, ocean waves diffract through the harbour
opening and spread out.
FM radio can be heard for a few meters after the tunnel opening
as the signal diffracts through
the opening.
Light rays diffract around your hair so people with long floppy
fringes can see diffraction
patterns in bright weather.
4.5.5 State the principle of superposition and explain what is
meant by constructive interference and by destructive interference.
Superposition is when two waves meet and effect each other.
The principle of superposition states that two waves add up in a
vector fashion as follows:
This is called constructive interference and happens when the
two waves are in phase.
path difference = n
This is called destructive interference and happens when the
waves are out of phase.
Path difference = (n+)
-
Allan Riddick
4.5.6 State and apply the conditions for constructive and for
destructive interference in terms of path difference and phase
difference. 4.5.7 Apply the principle of superposition to determine
the resultant of two waves.
-
Allan Riddick
5.1 Electric potential difference, current and resistance
5.1.1 Define electric potential difference.
The potential difference is defined as the work done per unit
charge to move a positive test charge
between A and B.
eCherenceEnergyDiffifferencePotentialD
arg=
The base unit for potential difference is the Joule per Coulomb
(JC-1).
5.1.2 Determine the change in potential energy when a charge
moves
between two points at different potentials.
To move a charge in an electric field work must be done. The
change in the electrical potential energy
(which is equal to the work done) is the potential
difference.
When the charge, q, moves from point A to point B it gains
electrical potential energy. Work must be
done to move the charge.
Change in potential energy = Force x distance
= F x d
= E x q x d
E is the Electric Field Strength and is explained further in
Topic 6
5.1.3 Define the electronvolt.
The joule is too large a measure of energy to be used at a
subatomic level. For very small energies
electronvolts (eV) are used.
1 eV = 1.6 x 10-19 J
5.1.4 Solve problems involving electric potential
difference.
-
Allan Riddick
5.1.5 Define electric current.
Electrical current is the flow of charged particles through a
material when a potential difference is
applied across it. By convention the current carriers are the
positively charged particles.
In a metallic conductor the charge carriers are electrons so the
conventional current flows in the
opposite direction to the charge carriers.
Electrical current is defined as the rate of flow of
electrical.
5.1.6 Define resistance.
Resistance is a measure of how easily a charge can flow in a
material. The resistance is defined as the
ration of the potential difference across a material to the
current flowing through it.
The unit of resistance is the ohm (). One ohm is defined as the
resistance of a material through
which a current of one amp flows when a potential difference of
one volt is applied across it.
5.1.7 Apply the equation for resistance in the form R=l / A
The resistance on a wire (at a constant temperature) depends
upon
Length
Cross sectional area
Resistivity.
The resistivity of a material tells us how well that material
conducts. Good conductors have a very
small resistivity (10-8 m). Insulators have a very large
resistivity (Glass 1012 m)
CurrentifferencePotentialD
cesis =tanRe
IVR =
TimeeChCurrent arg=
t
QI =
-
Allan Riddick
5.1.8 State Ohms law.
Ohms law is commonly written as
Voltage = Current x Resistance
V = I R
5.1.9 Compare ohmic and non-ohmic behaviour. In non-ohmic
behavior V and I are not proportional to each other. Examples of
this include light bulb
filaments and semi-conductor devises like diodes and
transistors.
5.1.10 Derive and apply expressions for electrical power
dissipation in resistors.
Electrical power is the rate that an electrical devise uses
energy.
RVRI
t
EP2
2===
5.1.11 Solve problems involving potential difference, current
and resistance.
Ohms Law
Providing the physical conditions such as temperature are kept
constant, the resistance is
constant over a wide range of applied potential differences and
therefore the potential difference is directly proportional to the
current.
-
Allan Riddick
5.2 Electric circuits
5.2.1 Define electromotive force (emf).
The emf is the amount of energy per unit charge supplied to a
circuit by a power source. For a call it is
the amount of chemical energy converted to electrical energy per
unit charge..
5.2.2 Describe the concept of internal resistance.
When a battery supplies a current to an external circuit it gets
warm. This is due to the battery having
a small internal resistance.
The Emf of the supply is the sum of the potential dropped across
the internal resistor and the external
resistor.
= Ir + IR
= Ir + Terminal Potential
Terminal Potential = - Ir
-
Allan Riddick
5.2.3 Apply the equations for resistors in series and in
parallel.
Resistors in Series
Resistors in Parallel
.....
11121
++=RRRTotal
RTotal = R1 + R2 + .
-
Allan Riddick
5.2.4 Draw circuit diagrams
5.2.5 Describe the use of ideal ammeters and ideal
voltmeters.
Ammeters are used to measure the current in a circuit. They are
connected in
series with the component under test. In order to have no effect
on the circuit
they should have a very small resistance. Ideal ammeters have
zero
resistance. This means that no potential difference is dropped
across them.
Voltmeters are used to measure the voltage in the circuit. They
are connected in
parallel with the component under test. Voltmeters have a very
high resistance so
that very little current is allowed to flow through them. An
ideal voltmeter has an
infinite resistance.
-
Allan Riddick
5.2.6 Describe a potential divider.
Resistors connected in parallel can be used to control voltages.
By changing the ratio of the resistors it
is possible to vary how much potential is dropped across either
V1 or V2.
5.2.7 Explain the use of sensors in potential divider
circuits.
Light Switch
When light stops shining on the LDR then its resistance will
increase. As the resistance changes the
potential difference dropped across it will change. This change
in potential can be detected by an
external circuit which can then switch lights on and off as
required.
21
2
RRRVV inout +
=
-
Allan Riddick
Fields and forces
This topic is best taught together so that the similarities and
differences between the three types of
field are discussed.
Fields are regions of space in which susceptible particles feel
a force:
A gravitational field is a region of space in which a mass feels
a force because of gravity.
An electrical field is a region of space in which a charge feels
a force because of another nearby
charge.
A magnetic field is a region of space where magnetic materials
experience a force.
These three types of fields are studied together because they
have similarities and the techniques for
performing calculations are similar too, but there are also
significant differences:
Gravity is always attractive and there is only one type of
mass.
Electric forces can be attractive or repulsive and we can have
negative or positive charge.
Magnetic forces can also be attractive or repulsive and there
are two types of magnetic pole
(North and South) these always appear in pairs.
6.1 Gravitational force and field
6.1.1 State Newtons universal law of gravitation.
Every point mass attracts every other point mass by a force
pointing along the line intersecting both
points. The force is proportional to the product of the two
masses and inversely proportional to the
square of the distance between the point masses:
6.1.2 Define gravitational field strength.
A gravitational field is a region of space in which a mass feels
a force because of gravity. Gravitational
field strength is the force per unit mass on a particle because
of the gravitational field.
6.1.3 Determine the gravitational field due to one or more point
masses.
Field strengths are vectors and therefore the gravitational
field due to one or more point masses can
be found by vector addition.
2r
GMmF =
Where
F is the magnitude of the gravitational force between the two
point masses,
G is the gravitational constant,
M is the mass of the first point mass,
m is the mass of the second point mass,
r is the distance between the two point masses.
m
Fg =
Where
g is the gravitational Field strength in NKg-1
F is the force experienced in N m is the mass of the object in
kg
-
Allan Riddick
61.4 Derive an expression for gravitational field strength at
the surface of a planet,
assuming that all its mass at concentrated at its centre.
The gravitational field strength at the surface of planet is
more commonly known as little g or g (at
the surface of the Earth it is 9.8 NKg-1)
The force experienced by a mass in a gravitational field is
given by
2r
GMmF =
And the gravitational field strength is defined as
m
Fg =
By combining these formulas the gravitational field strength due
to a point mass is given by
2r
GMg =
-
Allan Riddick
6.2 Electric force and field
6.2.1 State that there two types of electric charge
There are two types of electric charge. Positive and
Negative
6.2.2 State and apply the law of conservation of charge.
Charge can be added or removed from an object but it cannot be
destroyed.
Charge conservation is the principle that electric charge can
neither be created nor destroyed. The
quantity of electric charge is always conserved.
6.2.3 Describes and explain the difference in the electrical
properties of conductors and
insulators.
Conductors allow electric charges to pass through them. In a
metallic conductor the charges that flow
are electrons. An insulator is a material that does not allow
charges to flow.
6.2.4 State Coulombs law.
Coulombs law is used to calculate the force of attraction or
repulsion between two point charges.
20
21
4 rqq
Fpi
=
Where
F is the magnitude of the force between the two charges in
Newtons
0 is the permittivity of free space - 8.85x10-12 C2N-1m-2
q1 is the charge of the first point charge in Coulombs,
q2 is the charge of the second point charge in Coulombs,
r is the distance between the two point charge in meters.
6.2.5 Define electric field strength.
Electric field strength is defined as the force experienced per
coulomb by a small positive charge in an
electric field.
qFE =
Where
E is the electric field strength in NC-1
F is the force experienced but the charge in N
q is the charge on the object in C.
The electric field strength close to a sphere can be derived in
the same way as gravitational field
strength to be:
204 r
qEpi
=
6.2.6 Determine the electric field strength due to one or more
point charges.
-
Allan Riddick
Field strengths are vectors and therefore the electric field due
to one or more point charges can be
found by vector addition.
6.2.7 Draw the electric field patterns for different charge
configurations.
Field lines around a charged sphere
Field lines due to a dipoles
Field lines due to parallel plates
The region between a set of parallel plates is a uniform
electric field. The field lines are parallel and
equally spaced telling us that the electric field strength is
constant.
6.2.8 Solve problems involving electric charges, forces and
fields.
-
Allan Riddick
6.3 Magnetic force and field
6.3.1 State that moving charges give rise to magnetic
fields.
When an electric current flows through a wire a magnetic field
is created.
6.3.2 Draw magnetic field patterns due to currents.
The direction of the field lines surrounding a wire can be found
using a right hand rule.
The magnetic field caused by the current can be increased by
coiling the wire, creating a solenoid.
6.3.3 Determine the direction of the force on a current-carrying
conductor in a magnetic
field.
When a current carrying wire is placed between the poles of a
magnet it experiences a force. This
force causes the wire to jump
The direction that the wire will jump can be predicted using
Fleming Left Hand Rule. Line your thumb,
first and second fingers as shown below.
-
Allan Riddick
6.3.4 Determine the direction of the force on a charge moving in
a magnetic field.
6.3.5 Define the magnitude and direction of a magnetic
field.
6.3.6 Solve problems involving magnetic forces, fields and
currents.
BIlF =
Where
F is the force experienced by the wire, measured in Newtons
B is the magnetic field strength, measured in Tesla
I is the current flowing through the wire, measured in Amps l is
the length of wire between the poles of the magnet, measured in
Meters.
-
Allan Riddick
7.1 The atom
7.1.1 Describe a model of the atom that features a small nucleus
surrounded by electrons.
Facts and figures about the atom.
Diameter of a nucleus 10-15m
Diameter of an atom 10-10m
Mass of nucleus 10-27kg
Mass of a proton 1.6731027 kg
Mass on an neutron 1.6751027 kg
Mass of an electron 9.1101031 kg
Charge on a proton -1.60x10-19C
Charge on an electron -1.60x10-19C
7.1.2 Outline the evidence that supports a nuclear model of the
atom.
The best evidence for the nuclear model of the atom is the
Geiger-Marsden Gold leaf experiment. They
fired a beam of charged particles at a single layer of gold
molecules and observed what happened.
According to the JJ Thomson Plum Pudding model they were
expecting the charged particles to pass
straight through.
They were very surprised that some of the alpha particles where
deflected as they passed through the
gold. From this they deduced that there the atom was made up of
a small massive positively charged
nucleus surrounded by space.
7.1.3 Outline one limitation of the simple model of the nuclear
atom.
The problem with this theory was that accelerating charges are
known to lose energy. If the orbiting
electrons were to lose energy they would spiral into the
nucleus. The Rutherford model cannot explain
to us how atoms are stable.
-
Allan Riddick
7.1.4 Outline evidence for the existence of atomic energy
levels.
This model was developed further by Niels Bohr. He suggested
that the electrons orbit the nucleus
rather like a planet orbits the sun. The radius of Bohrs
electrons depended on the energy they had.
He also suggested that they could only move in certain
orbits.
When the electrons moved from a high energy state to a lower
energy state they emitted a photon of
light. The frequency of the light depends on the difference
between the energy levels.
As there are a fixed number of energy levels only a few
wavelengths of light are given out. This
results in a line spectrum. Each individual element has distinct
energy levels and therefore the
emission spectra can be used to identify them.
Nuclear structure
7.1.5 Explain the terms nuclide, isotope and nucleon.
Nuclide protons and neutrons that form a nucleus
Isotope nuclei that have the same number of protons but a
different number of neutrons.
Nucleon The collective name for particles that are found in the
nucleus (protons and Neutrons)
hf = E1-E2 Where
h Planks constant (6.02 x 10-34 m2 kg s-2)
f Frequency of the emitted photon (Hz)
E1 Energy level before emitting photon (J) E2 Energy level after
photon has been emitted (J)
-
Allan Riddick
7.1.6 Define nucleon number A, proton number Z and neutron
number N.
Nucleon Number, A The number of protons and neutrons that are in
the nucleus.
Proton Number, Z The number of protons that are in the
nucleus.
Neutron Number, N The number of neutrons that are in the
nucleus.
7.1.7 Describe the interactions in a nucleus.
According to our knowledge of electrostatics a nucleus should
not be stable. Protons are positive
charges so should repel each other. There must be another force
in the nucleus that overcomes the
electrostatic repulsion and hold the nucleus together. This
force is called the strong nuclear force.
Strong nuclear forces must be very strong to overcome the
electrostatic forces. They must also have a
very small range as they are not observed outside of the
nucleus.
Neutrons have some involvement in strong nuclear forces. Small
nuclei have equal numbers of
protons and neutrons. Larger nuclei, which are harder to hold
together, have a greater ratio of
neutrons to protons.
-
Allan Riddick
7.2 Radioactive decay
7.2.1 Describe the phenomenon of natural radioactive decay.
7.2.2 Describe the properties of alpha and beta particles and
gamma radiation.
7.2.3 Describe the ionizing properties of alpha and beta
particles and gamma radiation.
7.2.4 Outline the biological effects of ionizing radiation.
7.2.5 Explain why some nuclei are stable while others are
unstable.
Half-life
7.2.6 State that radioactive decay is a random and spontaneous
process and that the rate of
decay decreases exponentially with time.
7.2.7 Define the term radioactive half-life.
7.2.8 Determine the half-life of a nuclide from a decay
curve.
7.3 Nuclear reactions, fission and fusion
Nuclear reactions
7.3.1 Describe and give an example of an artificial (induced)
transmutation.
7.3.2 Construct and complete nuclear equations.
7.3.3 Define the term unified atomic mass unit.
7.3.4 Apply the Einstein massenergy equivalence
relationship.
7.3.5 Define the concepts of mass defect, binding energy and
binding energy per nucleon.
7.3.6 Draw and annotate a graph showing the variation with
nucleon number of the binding
energy per nucleon.
7.3.7 Solve problems involving mass defect and binding
energy.
Fission and fusion
7.3.8 Describe the processes of nuclear fission and nuclear
fusion.
7.3.9 Apply the graph in 7.3.6 to account for the energy release
in the processes of fission
and fusion.
7.3.10 State that nuclear fusion is the main source of the Suns
energy.
7.3.11 Solve problems involving fission and fusion
reactions.
-
Allan Riddick
-
Allan Riddick
8.1 Energy degradation and power generation
8.1.1 State that thermal energy may be completely converted to
work in a single process,
but that continuous conversion of this energy into work requires
a cyclical process and the
transfer of some energy from the system.
8.1.2 Explain what is meant by degraded energy.
The second law of thermodynamics states that it is impossible to
take heat from a hot object and use
it without losing some heat to the surroundings. Energy becoming
more spread out is known as the
degradation of energy.
Whenever thermal energy is converted into mechanical energy some
of the energy is degraded (lost)
to the environment.
8.1.3 Construct and analyse energy flow diagrams (Sankey
diagrams) and identify where
the energy is degraded.
Sankey diagram for a petrol engine.
8.1.4 Outline the principal mechanisms involved in the
production of electrical power.
Mechanical energy can be converted into electrical energy using
a generator of dynamo. A coil is
turned in a magnetic field. As the coil cuts the field lines,
electrons move round the coil. The
movement of electrons causes a potential difference which
results in a current flowing. A current has
been induced in the coil.
A more detailed explanation of electromagnetic induction can be
found in Unit 12, Electromagnetic
induction.
-
8.2.1 Identify different world energy sources.
Modern society requires a lot of energy. Most of the energy
recourses used by hum
make electricity or to make things move.
8.2.2 Outline and distinguish between renewable and non
A renewable source of energy cannot be used up. A non
and will eventually run out.
Renewable Energy
Solar
Wind
Hydroelectric
Wave
Tidal
Biofuels (Wood, ethanol)
Geothermal
8.2.3 Define the energy density
Energy density is the amount of energy that c
8.2.4 Discuss how choice of fuel is influenced by its energy
density.
The cost of transporting fuels is dependent on the fuel density.
A fuel with a low fuel density will be
expensive to transport.
8.2 World energy sources
8.2.1 Identify different world energy sources.
Modern society requires a lot of energy. Most of the energy
recourses used by hum
make electricity or to make things move.
8.2.2 Outline and distinguish between renewable and
non-renewable energy sources.
A renewable source of energy cannot be used up. A non-renewable
source of energy can be used up
Renewable Energy Non-Renewable Energy
Solar Coal
Wind Oil
Hydroelectric Gas
Wave Nuclear (Uranium)
Tidal
Biofuels (Wood, ethanol)
Geothermal
energy density of a fuel.
Energy density is the amount of energy that can be obtained per
kilogram of fuel.
8.2.4 Discuss how choice of fuel is influenced by its energy
density.
cost of transporting fuels is dependent on the fuel density. A
fuel with a low fuel density will be
Allan Riddick
Modern society requires a lot of energy. Most of the energy
recourses used by humans are used to
renewable energy sources.
renewable source of energy can be used up
an be obtained per kilogram of fuel.
cost of transporting fuels is dependent on the fuel density. A
fuel with a low fuel density will be
-
Allan Riddick
8.2.5 State the relative proportions of world use of the
different energy sources that are
available.
Worldwide Energy resources
8.2.6 Discuss the relative advantages and disadvantages of
various energy sources.
-
Allan Riddick
8.3 Fossil fuel power production
A fossil fuel fired power plant is and based on somewhat ancient
methods of energy production. The
fossil fuel is placed in a combustion chamber and burnt to
produce heat. In order to turn the heat
energy to electric energy, water is pumped around the combustion
chamber and the heat from the
chamber heats the water and it turns to steam. In the case of a
coal fired plant this heats the water to
1000C. The steam is used to turn a turbine which is attached to
a generator. The generator
generates converts the kinetic energy into electrical energy.
Meanwhile the used steam goes to a
condenser where it is cooled and turns to liquid water again;
this lets off the big clouds often seen
coming from these power plants. These clouds are nothing more
than steam. The water is then
pumped back into the combustion chamber to begin the cycle
again.
Coal Fired Power Station
8.3.1 Outline the historical and geographical reasons for the
widespread use of fossil fuels.
8.3.2 Discuss the energy density of fossil fuels with respect to
the demands of power
stations.
8.3.3 Discuss the relative advantages and disadvantages
associated with the transportation
and storage of fossil fuels.
8.3.4 State the overall efficiency of power stations fuelled by
different fossil fuels.
8.3.5 Describe the environmental problems associated with the
recovery of fossil fuels and
their use in power stations.
-
8.4 Non
Nuclear power
8.4.1 Describe how neutrons produced in a fission reaction may
be used to initiate further
fission reactions (chain reaction).
In a nuclear reactor a large nuclei, e.g. Uranium
smaller nuclei. The daughter nuclei have less mass than the
parent and so energy is released.
During the reaction two or 3 neutrons are released. They can
move on and collide with other uranium
nuclei and create a chain reaction. A cha
a moderator and if there is a large enough piece of fissional
material. The minimum amount of
material needed for a chain reaction to take place is called the
critical mass.
8.4.2 Distinguish between controlled nuclear fission (power
production) and uncontrolled
nuclear fission (nuclear weapons).
In a nuclear power station it is important that the chain
reaction is controlled. Only one neutron from
each reaction can be allowed to make fissio
reactor.
In a nuclear weapon the chain reaction is not controlled. The
fissionable material and a moderator are
mixed together.
8.4.3 Describe what is meant by fuel enrichment.
8.4 Non-fossil fuel power production
8.4.1 Describe how neutrons produced in a fission reaction may
be used to initiate further
fission reactions (chain reaction).
In a nuclear reactor a large nuclei, e.g. Uranium-236, is
bombarded with a neutron and spl
smaller nuclei. The daughter nuclei have less mass than the
parent and so energy is released.
During the reaction two or 3 neutrons are released. They can
move on and collide with other uranium
nuclei and create a chain reaction. A chain reaction will only
occur if the neutrons are slowed down by
a moderator and if there is a large enough piece of fissional
material. The minimum amount of
material needed for a chain reaction to take place is called the
critical mass.
between controlled nuclear fission (power production) and
uncontrolled
nuclear fission (nuclear weapons).
In a nuclear power station it is important that the chain
reaction is controlled. Only one neutron from
each reaction can be allowed to make fission. The other neutrons
are absorbed by control rods in the
In a nuclear weapon the chain reaction is not controlled. The
fissionable material and a moderator are
8.4.3 Describe what is meant by fuel enrichment.
Allan Riddick
8.4.1 Describe how neutrons produced in a fission reaction may
be used to initiate further
236, is bombarded with a neutron and splits into two
smaller nuclei. The daughter nuclei have less mass than the
parent and so energy is released.
During the reaction two or 3 neutrons are released. They can
move on and collide with other uranium
in reaction will only occur if the neutrons are slowed down
by
a moderator and if there is a large enough piece of fissional
material. The minimum amount of
between controlled nuclear fission (power production) and
uncontrolled
In a nuclear power station it is important that the chain
reaction is controlled. Only one neutron from
n. The other neutrons are absorbed by control rods in the
In a nuclear weapon the chain reaction is not controlled. The
fissionable material and a moderator are
-
Allan Riddick
99.3% of the uranium dug out of the ground is Uranium-238.
Uranium-238 will absorb neutrons but
will not fission so its presence in a nuclear reactor can hinder
the chain reaction. The fuel in the
reactor (or weapon) needs to have a much higher concentration of
Uranium-235. The raw uranium
must be enriched before it can be used. Commercial reactors use
fuel with 5% Uranium-235. Weapon
grade Uranium has over 85% Uranium-235.
8.4.4 Describe the main energy transformations that take place
in a nuclear power station.
8.4.5 Discuss the role of the moderator and the control rods in
the production of controlled
fission in a thermal fission reactor.
Moderator The moderator slows down the neutrons. If the neutrons
have too high an energy they
will pass straight thorough the uranium nuclei and fission will
not occur.
Control Rods Control rods are raised and lowered in the reactor
to control the rate of fission.
8.4.6 Discuss the role of the heat exchanger in a fission
reactor.
The whole reactor is housed within a large pressure vessel.
Pressurised gas is passed through the
reactor core and then takes the heat out to a heat exchanger.
The heat exchanger heats up water
turning it into steam. This steam is used to turn a turbine
which is connected to a generator. The
steam is cooled down in a condenser and then recirculated.
8.4.7 Describe how neutron capture by a nucleus of uranium-238
(238U) results in the
production of a nucleus of plutonium-239 (239Pu).
8.4.8 Describe the importance of plutonium-239 (239Pu) as a
nuclear fuel.
8.4.9 Discuss safety issues and risks associated with the
production of nuclear power.
8.4.10 Outline the problems associated with producing nuclear
power using nuclear fusion.
8.4.11 Solve problems on the production of nuclear power.
Solar power
8.4.12 Distinguish between a photovoltaic cell and a solar
heating panel.
A photovoltaic cell converts solar radiation directly into a
voltage.
Solar Heating panels absorb solar radiation and use it to heat
water. This water can be used
domestically and saves energy by reducing the amount of fuel
being used for heating.
8.4.13 Outline reasons for seasonal and regional variations in
the solar power incident per
unit area of the Earths surface.
8.4.14 Solve problems involving specific applications of
photovoltaic cells and solar heating
panels.
Hydroelectric power
8.4.15 Distinguish between different hydroelectric schemes.
This form of renewable energy probably is the most simple of
them all in terms of the concepts and
science involved. The kinetic energy of water moving downhill is
being used to turn a turbine which is
attached to a generator. The generator turns the kinetic energy
into electrical energy. A diagram of
this basic model is shown below.
-
A large store of water must be creat
power output means that a reservoir must be created.
having to be flooded in order to create the reservoir
These problems are often overlooked as the amounts of energy
produced are massive
power is currently the only widely used renewable energy
source.
8.4.16 Describe the main energy transformations that take place
in
8.4.17 Solve problems involving hydroelectric schemes.
Wind power
8.4.18 Outline the basic features of a wind generator.
Wind power relies on the conversion of
There is a great deal of kinetic energy
Different parts of the atmosphere are heated to different
temperatures. The temperature differences
causes pressure differences, due to hot air risi
There are some advantages and disadvantages of the use of wind
power. The advantages are that its
a very clean production, it is renewable and the source of
energy is free. The disadvantages are that
the source of energy is unreliable as there could be a day
without wind, it has a low energy density, it
can be seen as visual pollution as it spoils the countryside, it
can be noisy and the best positions for
wind are usually far away from centers of population
8.4.19 Determine the power that maybe delivered by a wind
generator, assuming that the
wind kinetic energy is completely converted into mechanical
kinetic energy, and explain why
this is impossible.
8.4.20 Solve problems involving wind power.
Wave power
8.4.21 Describe the principle of operation of an oscillating
water column (OWC) ocean
energy converter.
must be created for this method to be viable. Constantly produce
an elevated
power output means that a reservoir must be created. This causes
the problem of an area of land
having to be flooded in order to create the reservoir, this can
cause ecological problems.
overlooked as the amounts of energy produced are massive
widely used renewable energy source.
8.4.16 Describe the main energy transformations that take place
in hydroelectric schemes.
8.4.17 Solve problems involving hydroelectric schemes.
8.4.18 Outline the basic features of a wind generator.
Wind power relies on the conversion of kinetic energy in the
wind into electrical energy
There is a great deal of kinetic energy in the wind.
Different parts of the atmosphere are heated to different
temperatures. The temperature differences
pressure differences, due to hot air rising or cold air sinking,
which result in air flows
There are some advantages and disadvantages of the use of wind
power. The advantages are that its
a very clean production, it is renewable and the source of
energy is free. The disadvantages are that
able as there could be a day without wind, it has a low energy
density, it
can be seen as visual pollution as it spoils the countryside, it
can be noisy and the best positions for
wind are usually far away from centers of population.
8.4.19 Determine the power that maybe delivered by a wind
generator, assuming that the
s completely converted into mechanical kinetic energy, and
explain why
8.4.20 Solve problems involving wind power.
8.4.21 Describe the principle of operation of an oscillating
water column (OWC) ocean
Allan Riddick
onstantly produce an elevated
his causes the problem of an area of land
ecological problems.
overlooked as the amounts of energy produced are massive.
Hydroelectric
hydroelectric schemes.
electrical energy using turbines.
Different parts of the atmosphere are heated to different
temperatures. The temperature differences
which result in air flows.
There are some advantages and disadvantages of the use of wind
power. The advantages are that its
a very clean production, it is renewable and the source of
energy is free. The disadvantages are that
able as there could be a day without wind, it has a low energy
density, it
can be seen as visual pollution as it spoils the countryside, it
can be noisy and the best positions for
8.4.19 Determine the power that maybe delivered by a wind
generator, assuming that the
s completely converted into mechanical kinetic energy, and
explain why
8.4.21 Describe the principle of operation of an oscillating
water column (OWC) ocean-wave
-
Allan Riddick
Wave power uses the kinetic energy of waves to generate
electrical energy. One of the successful
techniques is using the oscillating water column (OWC). The OWC
is a device built on land. In-coming
waves force air in and out of a turbine, which generates
electrical energy. The particular design of the
turbine (Wells turbine) means of that it generates electrical
energy whatever the direction of flow of
the air.
8.4.22 Determine the power per unit length of a wavefront,
assuming a rectangular profile
for the wave.
8.4.23 Solve problems involving wave power.
-
Allan Riddick
8.5 Greenhouse effect
Solar radiation
8.5.1 Calculate the intensity of the Suns radiation incident on
a planet.
8.5.2 Define albedo.
Albedo is the term used to describe the ratio of reflection to
absorption for an object. The Albedo for a
white shiny object is high. Snow reflects most of the radiation
incident on it and has an Albedo of
around 90%. The average Albedo for the earth is about 30%.
8.5.3 State factors that determine a planets albedo.
There are a number of factors which affect a planets albedo:
Firstly the albedo varies across the surface of the planet due
to:
Land coverage i.e. land or water or snow
Vegetation coverage
Latitude
Time of year (Because it affects the vegetation)
The greenhouse effect
8.5.4 Describe the greenhouse effect.
The greenhouse effect consists of the earth receiving short
wave-length radiation from the sun, and
this then causes the surface to warm up. The Earth will then
emit infra-red radiation (longer
wavelengths than absorbed, because the earth is cooler. Some of
this outgoing radiation is intercepted
and absorbed by the greenhouse gases and after which it is
re-radiated in all directions.
If the energy radiated and the energy absorbed is equal the
temperature of the planet will remain
constant. But that isnt happening at the moment more energy is
absorbed than radiated, and so the
earth gets warmer.
Truck Analogy of the Greenhouse Effect
If only 10% of the greenhouse gases are radiated from the Earth,
then the Earth supposedly should be
heating up but its not. So why is this so?
Well, we could use an analogy of a truck delivering sand. Each
time it delivers 100kg of sand, and 10%
of the sand at the drop of point is carried away. At the
beginning the amount of sand increases rapidly
seeing as more is brought in then taken out. But eventually
those 10% taken out will be equal to the
100kg brought in and the load would stabilize. The same is true
for the earths temperature. A graph is
shown below of this effect.
8.5.5 Identify the main greenhouse gases and their sources.
0
200
400
600
800
1000
0 20 40 60 80
Load against Time
Load (kg)
-
The Greenhouse Gases that occur in the earths atmosphere
are:
Methane
Water
Carbon Dioxide
Combustion of fossil fuels releases this gas into the atmosphere
and it has a very important role
in the greenhouse effect. It is naturally removed from the
atmosphere by Carbon Fixation by
plants in photosynthesis.
Nitrous Oxide
Livestock and industries are big producers of this and it has a
significant effect as it can remain
in the upper atmosphere for a long time as it is harder to
fixate.
Ozone
This is responsible for absorbing high energy UV photons which
could be harmful to living
organisms.
However these can be changed in their ratios due to human
industry and technology.
8.5.6 Explain the molecular mechanisms by which greenhouse gases
absorb infrared
radiation.
Each of these gases absorbs certain wavelengths of the
electromagnet
They do as a result of resonance. The natural frequency of the
oscillation of the bonds within the
molecules of the gas in within the infrared region. If the
driving frequency (from the radiation emitted
by the Earth) is equal to the natural frequency of the molecule,
resonance will occur. The amplitude of
the molecules vibrations increases and the temperature
increases. The absorption will take place at
specific frequencies depending on the molecular bonds.
8.5.7 Analyse absorption graphs to compare the relative effects
of different greenhouse
gases.
Below is an absorption spectrum graph for each of the greenhouse
gases, thus showing that each gas
absorbs a different wavelength of radiation.
8.5.8 Outline the nature of black
8.5.9 Draw and annotate a graph of the emission spectra of black
bodies at different
temperatures.
Black objects are the best absorbers and radiators of
radiation.
a black body emitter is shown below. The
The Greenhouse Gases that occur in the earths atmosphere
are:
Combustion of fossil fuels releases this gas into the atmosphere
and it has a very important role
in the greenhouse effect. It is naturally removed from the
atmosphere by Carbon Fixation by
nd industries are big producers of this and it has a significant
effect as it can remain
in the upper atmosphere for a long time as it is harder to
fixate.
This is responsible for absorbing high energy UV photons which
could be harmful to living
However these can be changed in their ratios due to human
industry and technology.
8.5.6 Explain the molecular mechanisms by which greenhouse gases
absorb infrared
Each of these gases absorbs certain wavelengths of the
electromagnetic waves emitted by the sun.
They do as a result of resonance. The natural frequency of the
oscillation of the bonds within the
molecules of the gas in within the infrared region. If the
driving frequency (from the radiation emitted
to the natural frequency of the molecule, resonance will occur.
The amplitude of
the molecules vibrations increases and the temperature
increases. The absorption will take place at
specific frequencies depending on the molecular bonds.
rption graphs to compare the relative effects of different
greenhouse
Below is an absorption spectrum graph for each of the greenhouse
gases, thus showing that each gas
absorbs a different wavelength of radiation.
ck-body radiation.
8.5.9 Draw and annotate a graph of the emission spectra of black
bodies at different
objects are the best absorbers and radiators of radiation. The
range of wavelengths
body emitter is shown below. The peak of the graph represents
the most
Allan Riddick
Combustion of fossil fuels releases this gas into the atmosphere
and it has a very important role
in the greenhouse effect. It is naturally removed from the
atmosphere by Carbon Fixation by
nd industries are big producers of this and it has a significant
effect as it can remain
This is responsible for absorbing high energy UV photons which
could be harmful to living
However these can be changed in their ratios due to human
industry and technology.
8.5.6 Explain the molecular mechanisms by which greenhouse gases
absorb infrared
ic waves emitted by the sun.
They do as a result of resonance. The natural frequency of the
oscillation of the bonds within the
molecules of the gas in within the infrared region. If the
driving frequency (from the radiation emitted
to the natural frequency of the molecule, resonance will occur.
The amplitude of
the molecules vibrations increases and the temperature
increases. The absorption will take place at
rption graphs to compare the relative effects of different
greenhouse
Below is an absorption spectrum graph for each of the greenhouse
gases, thus showing that each gas
8.5.9 Draw and annotate a graph of the emission spectra of black
bodies at different
range of wavelengths emitted for
of the graph represents the most intense wavelength.
-
Allan Riddick
The peak wavelength can be calculated using Wiens Law.
8.5.10 State the StefanBoltzmann law and apply it to compare
emission rates from
different surfaces.
The Stefan-Boltzmann law relates the total energy emitted per
unit area by a black body emitter to its
temperature.
8.5.11 Apply the concept of emissivity to compare the emission
rates from the different
surfaces.
The surface of the earth is not a perfect black body emitter.
Emissivity compares the rate at which a
body radiates energy to the rate at which a black body emitter
at the same temperature emits
radiation.
8.5.12 Define surface heat capacity Cs.
The surface heat capacity is the energy that is required to
raise 1m3 of the surface of a planet by 1C.
8.5.13 Solve problems on the greenhouse effect and the heating
of planets using a simple
energy balance climate model.
=Power emitted by object per unit area
Power radiated by a black body at the same temperature
!" ## = $%& Stefan-Boltsmann Law
Where = 5.67 x 10-8 W m-2 K-4
'()* =+
%
Wiens Law
Where max Wavelength of maximum intensity
T Temperature of black body B constant = 2.89 x 10-3 mK
-
Allan Riddick
8.6 Global warming
Global warming
8.6.1 Describe some possible models of global warming.
8.6.2 State what is meant by the enhanced greenhouse effect.
The enhanced greenhouse effect is believed to be caused by the
increase in production of greenhouses
gases by humans.
8.6.3 Identify the increased combustion of fossil fuels as the
likely major cause of the
enhanced greenhouse effect.
Combustion of fossil fuels releases carbon dioxide into the
atmosphere. The use of fossil fuels
increased significantly during the second half of last century.
This resulted in a increase in the amount
of carbon dioxide in the atmosphere and is believed to have
resulted in an increase in the average
temperature of the earth.
8.6.4 Describe the evidence that links global warming to
increased levels of greenhouse
gases.
8.6.5 Outline some of the mechanisms that may increase the rate
of global warming.
8.6.6 Define coefficient of volume expansion.
The coefficient of volume expansion tells us the change in
volume of a substance per degree change in
temperature.
8.6.7 State that one possible effect of the enhanced greenhouse
effect is a rise in mean sea-
level.
If the average temperature of the oceans is caused to rise then
the mean sea level will rise. In the
past 100 years the mean sea level has risen by 20cm.
The rate that the sea level will rise is difficult to predict
due to the difficulty in accurately measuring
the volume increase of water. Water that is between 0 and 4C has
a negative volume coefficient so at
these temperatures it will contract as it warms.
Another factor is the ice that covers the land. As this melts it
will run into the sea causing the levels to
rise by an unknown amount.
Melting glaciers will have little effect on sea levels as they
already displace their own mass of water.
8.6.8 Outline possible reasons for a predicted rise in mean
sea-level.
8.6.9 Identify climate change as an outcome of the enhanced
greenhouse effect.
Global warming will cause changes to the climate. Models predict
that it will become warmer closer to
the equator and wetter in the northern hemisphere.
Some models predict that as there is more energy in the
atmosphere storms will become more
frequent and powerful.
=.
./
Where coefficient of volume expansion measured in K-1 V increase
in volume measured in m3 Vo initial volume of water measured in
m3
increase in temperature measured in K
-
Allan Riddick
8.6.10 Solve problems related to the enhanced greenhouse
effect.
8.6.11 Identify some possible solutions to reduce the enhanced
greenhouse effect.
Reduction in the consumption of fossil fuels would reduce the
enhanced greenhouse effect. Strategies
include:
Changing human activities that cause pollution
o Using energy saving light bulbs
o Improving efficiency of energy production
o Using electric and hybrid vehicles
o Replace fossil fuels with renewable or nuclear energy
Reducing the pollutants at the point of emission
o Capture carbon dioxide and store it underground
o Reduce methane emission from cows by diet
Clean up and restoration
o Plant more trees to act as a carbon sink
o Add iron to oceans to remove carbon dioxide from the air
8.6.12 Discuss international efforts to reduce the enhanced
greenhouse effect.
IPCC International Panel on Climate Change
The IPCC was established to provide the decision-makers and
others interested in
climate change with an objective source of information about
climate change. The
IPCC does not conduct any research nor does it monitor climate
related data or
parameters. Its role is to assess on a comprehensive, objective,
open and
transparent basis the latest scientific, technical and
socio-economic literature
produced worldwide relevant to the understanding of the risk of
human-induced
climate change, its observed and projected impacts and options
for adaptation
and mitigation.
http://www.ipcc.ch
Kyoto Protocol The Kyoto Protocol is a legally binding agreement
under which industrialized
countries will reduce their collective emissions of greenhouse
gases by 5.2%
compared to the year 1990 (but note that, compared to the
emissions levels that
would be expected by 2010 without the Protocol, this target
represents a 29%
cut). The goal is to lower overall emissions from six greenhouse
gases - carbon
dioxide, methane, nitrous oxide, sulphur hexafluoride, HFCs, and
PFCs -
calculated as an average over the five-year period of 2008-12.
National targets
range from 8% reductions for the European Union and some others
to 7% for the
US, 6% for Japan, 0% for Russia, and permitted increases of 8%
for Australia
and 10% for Iceland."
http://www.kyotoprotocol.com
APPCDC Asia-Pacific Partnership on Clean Development and
Climate
APP partners Australia, Canada, China, India, Japan, Korea, and
the United States
have agreed to work together and with private sector partners to
meet goals for
energy security, national air pollution reduction, and climate
change in ways that
promote sustainable economic growth and poverty reduction. The
Partnership will
focus on expanding investment and trade in cleaner energy
technologies, goods
and services in key market sectors.
http://www.asiapacificpartnership.org