Transcript
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PHYSICS STUDY NOTES IGCSE EDEXCEL;
SECTION A: Forces and motions
Speed = distance/ time
Instantaneous speed is the speed of an object from one instant to the other as theaccelerator or brake is used. Displacement is the distance travelled in a particular
direction from a specic point.
Velocity is the rate of motion per unit time. It is how fast the object is travellin with
a direction.
Velocity = displacement/time taken
!cceleration is the rate at which objects chane their velocities.
!cceleration = "nal velocity # initial velocity$/ time taken
%orces are vector &uantities. 'here is friction( weiht of object) reaction force by the
*arth and the force of object i.e. push. 'here are many forces such as air resistance(
up thrust( manetic( electrostatic and nucleus. If you apply a force to an elastic
band it chanes shape. It will stretch if put under tension and would shorten if
compressed.
Sprins chane shape when a force is applied to them and return back to oriinal as
soon as the force has been removed. +ooke,s law states that the e-tension of sprin
is directly proportional to the force applied. 'he elastic limit is when the sprin
starts to stretch more for each successive increase in the load force. nce it has
passed this limit the sprin has chaned shape permanently and will not return to
its oriinal lenth.
'he acceleration of an object is aected by both its mass and the force applied to it.
%orce = mass - acceleration
'he stoppin time is the sum of thinkin distance and brakin distance. 0eaction
time could be aected by the ae of the driver( if the driver is tired( if the driver is
under alcohol or drus. It could also be due to poor eyesiht. 1reakin distance
could be aected by the mass of the vehicle( the speed the vehicle is oin on( road
conditions and conditions of the tyres. 'he bier the mass of the car the loner thebrakin distance.
2eiht = mass - ravitational pull.
bjects fallin e-perience two forces) weiht force by ravity and the opposin dra
force.
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Staes of air resistance and acceleration) air resistance is very small but starts to
increase. 'he air resistance increases. 'hey are the same 3terminal velocity4 and
therefore have a balanced amount of acceleration and resistance. 'he lare air
resistance starts to decelerate. !ir resistance decreases until they are the same as
weiht and therefore reach another terminal velocity. n the round( the weiht is
e&ual to the upward force.
5omentum is a measure of how di6cult it is to stop somethin that is movin. It is
a vector &uantity.
5omentum = mass - velocity. It is measure in km/s.
%orce = chane in momentum/ time taken
5omentum will remain constant as lon as there is no interference and the system
is isolated.
5omentum before = momentum after
57V7 8 59V9 = 5:V:
Impulse is the chane in momentum
%orce - time = chane in momentum
If you increase the time( you decrease the force on the object. ;ars are desined
with various safety features that increase the time over which he car,s momentum
chanes in an accident. 'hese include seat belts( crumple
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>? derees and a perpendicular is the force that will have the best eect on the
door.
Sum of anticlockwise = sum of clockwise
;ounter balance is the thin needed to balance out a lon part of a pivot. 'he
centre of ravity is if you support the object at this point there is no turnin
moment. It is also called the centre of mass. In a symmetrical card the centre of
ravity will be located where the a-es meet. ! stable object is one that is di6cult to
push over.
'he *arth is one of the @ planets that orbit the sun. 'he orbits of planets are
elliptical with the sun close to the centre.
'he further the planet is away from the sun( the loner it takes for the planet to
orbit the sun once. 'he closer the planet is from the sun( the hotter the surfacetemperature of the planet.
'he strenth of ravity on a planet or moon is called its ravitational eld strenth.
Alanets are held in orbit by the ravitational pull of the sun.
5oons are natural objects that orbit a planet. 5oons are nonBluminous objects. 2e
see them because they reCect liht from the sun.
;omets orbit the sun. 'hey are appro-. 7B:? km in diameter and are made of dust
and ice. 'heir orbits are very elonated. !s a comet et closer to the sun( the
ravitational forces actin upon it increase and it speeds up. !s the opposite end ofits orbit( the ravitational forces are much smaller and the comet therefore travels
much slower.
!steroids are minor planets or rocks that orbit the sun. 'hey vary in si
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eostationary is the orbital period of a communication satellite which is 9E hours so
that it remains above the same part of the *arth,s surface. It can,t be interrupted or
damae.
SECTION : E!ectricit"
0in circuits consist of) the live wire which provides the path alon which the
electrical enery from the power station travels. It has an alternatin current
between neative and positive. 'he neutral wire completes the circuit. 'he *arth
wire usually has no current Cowin throuh it. It is there to protect you if an
appliance develops a fault.
'he outer part of a plu is called a casin and is made out of plastic. Alastic is a
ood insulator. ;onnections to the circuits are made out of three brass pins as brass
is an e-cellent conductor of electricity.
5any plus contain a fuse. 'he fuse is usually in the form of a cylinder or cartride
which contains as a thin piece of metal that has a low meltin point. If the current
ets too hih( then the metal melts( the circuit breaks and the current stops Cowin.
! fuse si
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2hen the switch is connected to the neutral wire then the electricity can still Cow
throuh the appliance and the user could still et shocked. +owever while it is
connected to the live wire then the person cannot et shocked.
Aower = current - voltae. Aower is measured in watts( current is measured in amps
and voltae is measured in volts.
*nery = power - time. *nery is measured in joules( power is measured watts and
time is measured in seconds.
!lternatin current is when current Cows in two ways( whereas direct current is only
in one way.
;hare 0elative mass 2here it is foundArotons 87 positive 7 In the nucleuseutrons ? neutral 7 In the nucleus*lectrons B7 neative 7/7@>> ut of the
nucleus
!toms normally have an e&ual amount of protons compared to the amount of
electrons( but if it is not it is either a positive or neative ion. If an unchared plastic
rod is rubbed with an unchared cloth( it is possible for them to become chared by
friction. 'he rod becomes positive and the cloth becomes neative. 'he rubbin
action doesn,t create or produce a chare but instead separates the chares as it
transfers the electrons from one of the objects to the other
If the chares are the same( they repel. If the chares are opposite( they attract.
2hen a chared object meets an unchared object( the positive or neative chares
are attracted to the opposite chare and repel chares that are the same
backwards.
'he old leaf electroscope) the electroscope is unchared. 'he rod is positively
chared. 'he electrons are attracted to the rod and move upwards. 'he bottom now
has more protons than electrons. 'he protons on the bottom and in the old leaf
repel and the old moves further. 2hen you put your ner on it( electrons from the
electroscope o to the round( makin the electroscope have a balance of electrons
and protons at the bottom. 2hen you put the positively chared rod aain( the
electrons move upwards and there is less repulsion so the old oes downwards.*arthin is when electrons are released down to *arth.
*lectrostatic paint sprayin) as the droplets emere from the spray un( they are
chared. !s the droplets all carry the same chare they repel and spread out
formin a ne spray. 'he metal bicycle frame has a wire attached to an electrical
supply ivin the frame the opposite chare. 'he paint droplets are therefore
attracted to the surface of the frame. 'here is the added benet that paint is
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attracted into places( such as tiht corners( that miht otherwise not receive such
as ood coatin.
5any modern printers use inkjets to direct a ne jet of ink drops onto paper. *ach
spot of ink is iven a chare so that as it falls between a pair of deCectin plates(
electrostatic forces direct it to the correct position. 'he chares on the plateschane hundreds of times each second so that each drop falls in a dierent position(
formin pictures and words on the paper as re&uired.
Ahotocopiers) the drum is chares with a positive chare) Imae of object to be
copied is formed here. ;hare stays only where imae is dark. 'oner drops on to
drum and sticks to chared areas. Surplus toner is removed. Aaper is pressed
aainst toner imae to ive imae on paper. Aaper is heated to melt toner imae.
'his forms permanent imae on paper.
*lectrostatic precipitators) as the smoke initially rises in the chimney( it passes
throuh a mesh of wires that are hihly chared. !s they pass throuh the mesh(
the ash and dust particles become neatively chares. +iher up the chimney these
chared particles are attracted by and stick to lare( metal earthed plates.
Aroblems with static electricity) as aircrafts Cy throuh the air( they can become
chared with static electricity and the hue dierence in potential causes the
chares to escape to the earth durin refuelin which can easily cause an e-plosion.
'his can be solved earthin the plane as soon as it lands. 'elevisions screens and
monitors become chared with static electricity as they are used. 'hese chares
attract liht unchared particles such as dust. ur clothin( under certain
circumstances( becomes chared with static electricity. 2hen we remove the
clothes there is the possibility of receivin a small electric shock as the charesescape to *arth.
;onductors allow electrons to Cow easily throuh them. 2hereas( insulators don,t
allow electrons to Cow easily. ;onductors could be metals and insulators could be
plastic.
2e measure the si
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past. 'he component with a hiher resistance will have a hiher voltae. 'he
component with a hiher resistance will have a lower current.
!ll
components in a circuit oer some resistance to the Cow of chare. Some allow
chares to pass throuh very easily losin very little of their enery i.e. connectin
wires. 'hey have low resistance. 'he Cow of current throuh some components is
not so easy and a sinicant amount of enery is used to move the chares throuhthem. 'his enery is converted into other forms( usually heat. ;omponents like this
one have a hih resistance.
2e measure the resistance of a component by comparin the si
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%i-ed resistors are included in circuits to control the si
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2avelenth is the distance between similar points from one to the other. 'rouh to
trouh or crest to crest.
'he number of waves produced each second by a source( or the number passin a
particular point each second is called the fre&uency. It is measured in hert
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waves are emitted by a transmitter. !s they cross an aerial( they are detected and
the information they carry can be received. Gses include radios and 'V,s.
Special electric circuits produce microwaves which are uided into rotatin
reCectors that send the microwaves in all directions. 'he microwaves are reCected
in all directions until they hit the food( where they are absorbed so the food etshotter. 'hey are used for communications as they pass throuh the *arth,s
atmosphere easily and are used to carry sinals to orbitin satellites. . 'he hotter an
object is the more enery it will emit as infraBred. Special waves can be used to
create imaes especially in the absence of visible liht. 'hey could be used to track
criminals. 'hey are used in remotes and can only work over short distances.
Visible liht is the part of the electromanetic spectrum that is visible to the human
eye. It is used for readin compact discs( communications and lookin inside the
body of patients. 'hey include colors such as red( orane( yellow( reen( blue(
purple and indio.
GV liht causes tan( but overe-posure will lead to sunburn and skin cancer and
blindness. 'hese can be protected by skin cream or protective oles. It is used in
Cuorescent tubes are GV tannin lamps.
HBrays pass easily throuh soft body tissue but it can,t pass throuh bones. !s a
result it can be used to check people,s bones. *-posure to too much HBray can
cause cancer. 'hey have to stand behind lead screens or to wear protective
clothin. amma rays are hih penetratin waves which cause damae to livin
cells such as mutations that lead to cancer at very small doses( however at lare
does it can be stron enouh to kill cancer cells completely.
'o send a messae usin a diital sinal( the information is converted into a
se&uence of numbers called a binary code. 'hese numbers are then converted into
a series of electrical pulses sent down the telephone lines.
! sinal that is converted into electrical voltaes or currents that vary continuously
is called an analoue( whereas a sinal that is converted into binary code is called a
diital sinal. Diital sinals are easy to reenerate whilst analoue sinals aren,t
and can be easily distorted.
bjects that emit their own liht are called luminous. 2hen the emitted liht enters
our eyes we can see the object. 5ost objects are nonBluminous and don,t emit liht.
2e see these nonBluminous objects because of the liht they reCect. Fiht waves
are transverse waves which can be reCected( refracted or diracted. 2hen a ray of
liht strikes a plane mirror( it is reCected so that the anle of incidence is e&ual to
the anle of reCection.
5irrors are often used to chane the direction of a ray of liht. It is used in
periscopes.
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Aroperties of an imae in a plane mirror) the imae is as far behind as the object in
front( the imae is the same si
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2hen white liht passes throuh a prism( it emeres as a band of colors called a
spectrum. 'he spectrum is formed because white liht is a mi-ture of colors and
each color travels throuh the prism at a slihtly dierent speed so each color is
refracted at a dierent anle. Since the prism has a dierent refractive inde- for
each color( each color emeres at dierent speeds and dierent anles.
!s the speaker cone moves to the riht( it pushed air molecules closer toether(
creatin compression. 'hese particles then push aainst neihborin particles so
the compression appears to be movin. 1ehind the compression there is an area
where all of the particles spread out. 'his is called rarefaction. 2hen this is
repeated many times( a lonitudinal wave is formed.
2hen the waves hit the ear( they strike the ear drum and make it vibrate. 'hese
vibrations are chaned into electrical sinals( which are detected by the brain.
Sound waves can travel throuh) solidsJ this is why we can hear people in dierent
rooms. Fi&uidsJ this is why underwater animals can communicate. asesJ this is why
humans can talk to each other.
Sound waves can,t travel throuh a vacuum because there are no particles for the
vibrations to be carried. 'he speed of sound depends on the temperature and
pressure of the medium. Kou can measure the speed of sound by usin echoes. Kou
stand is a sinicant distance from a wall and then multiply the distance by 9 and
divide it by the time.
Kou can measure the speed of sound by usin a resonance tube lled with water
until:/E of the wavelenth. ! sound of a known fre&uency would be made by a
tunin fork. 'he resonance will be heard when the lenth of the air in the tube is
e&ual to a &uarter of the wavelenth.
Speed of sound = fre&uency - wavelenth
Set the sinal enerator to ive a fre&uency of 7 k+
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Increasin the pitch increases the fre&uency of the waves. It makes the waves look
closer toether. %rom each compression to the other is the wavelenth and time.
Kou can nd the fre&uency of sound by usin a ;0. If you nd the time period then
divide by 7.
Gltra sounds are sounds that vibrate so &uickly( humans can,t hear them. +ih
fre&uency.
Infra sounds are sounds that vibrate so slowly( humans can,t hear them. Fow
fre&uency.
SECTION D: Ener%" Trans&ers
%or enery to be useful( we need to be able to transfer from one place to another
and to be able to convert it into whatever form we re&uire.
2hen you eat( you intake chemical enery. It is then burnt to enerate thermal
enery and to keep us warm. ur muscles convert the chemical enery into kinetic
enery. 'he movement enery could be used to make us speak.
*-amples of enery) liht( heat( sound( kinetic( electric( chemical( ravitational(
elastic and nuclear. 'he last E are all potential enery.
%or enery to be useful( we need to be able to transfer it from one place to another.
+owever there is always enery lost. It is called Lwasted, enery. *-amples includewhen the heater in a home converts electrical enery into heat enery( some of the
heat from the water is transferred from the water and onto the tank. !nother
e-ample is in a car( lots of the enery is converted into heat( sound and enery to
overcome the friction outside the car.
!n e-ample of enery conversions is when a cyclist eats food. 'he chemical enery
is converted into movement enery. 'he movement enery makes the wheels on
the bike to start movin. 'he movement of the wheel makes a enerator convert
the kinetic enery into electrical enery which turns on the lamp.
*nery is not created nor destroyed) it is just converted into dierent types.Ahysicists believe that the amount of enery in the universe is constant.
*nery transfer diarams show the enery input( the enery conversion process
and the enery output.
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Sankey diarams are a simpler and clearer way of showin what the input enery is
converted into. 'he width of each arrow is proportional to the amount of enery
involved.
*6ciency of a system is how much of the input enery is converted into enery that
you want.
Gseful enery output/ total enery output - 7??
*6ciency is a ratio and doesn,t have a measurement.
'here is a temperature called absolute
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moves into its place. ! ;onvection current is set up. 'he heater eventually heats up
the whole room.
'emperature is the sum of kinetic enery of all the particles in an object.
Since conduction is the main way heat can escape by( we have to know where
conduction occurs. ;onduction occurs in the walls( windows and the roof.
2ays to reduce heat loss in a house) loft insulation which is to put an insulatin
material in between the walls. ;avity wall insulation which is to put an insulatin
material in between the walls. %loor insulation which is the use of carpets( curtains
and more. Double la
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9N and the O* is PN. 0iht before the object hits the round( it has ?N A* and
7??N O*. 'his is all done with the assumption that friction isn,t taken into
consideration.
Oinetic enery of a movin object is calculated usin the formulaJ
O* = 7/95VQ9
O* = kinetic enery( 5 = mass( c = speed s&uared
2ork done liftin object = ain in A* = ain in O* of the object just before hittin
the round
Aower = work done/ time taken
Aower is the measure of how fast enery is transferred or transformed.
'he rowth of the world population means more people need warmth and food. ne
of the main enery resources available on our planet is its supply of fossil fuels.
*-amples include coal( oil and natural as. 'hey have been formed in the round
from dead veetation or tiny creatures by a process that has taken millions of years.
nce we have used them( it will take millions of years for new reserves of these
fuels to be formed. 'hey are therefore e-amples of nonBrenewable enery
resources.
! nonBrenewable enery resource is one that eectively can,t be replaces once it
has been used.
1urnin fossil fuels releases carbon dio-ide into the atmosphere. ;arbon dio-ide is a
reenhouse as. reenhouse ases trap the Sun,s heat in the *arth,s atmosphere
and cause the averae temperature of the atmosphere to rise. 'his eect is called
lobal warmin and causes chanes in the world,s and meltin of the polar ice caps.
5ost coal and oil contain some sulfur. 2hen they are burnt( they release sulfur
dio-ide. Sulfur dio-ide is then released into the atmosphere. It then combines with
water to form acid rain. It is possible to remove the sulfur from these fuels but his
costs lots of money. n the other hand( international areements are forcin
companies who emit lare &uantities of sulfur dio-ide to clean up their waste ases.
uclear reactors use uranium to produce enery. %or the nuclear reactor process( a
particular form or isotope of uranium is needed. !lthouh a reactor only needs a
small amount of uranium is needed( uranium is in limited supply. 'he uranium in the
*arth was formed before the solar system was formed( so once it has been used
there will be no further supplies. It is therefore cateori
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Stored
enery inthe formof fossil
fuels.;oal( as(
oil andnuclear
fuel.
+eatenery is
hihBpressuresteam.
5ovementenery ofrotatinturbine.
*lectricaleneryoutput.
'he disadvantaes of nuclear power are the risk of accidents and the problem of
disposal of radioactive materials once the power station has nished with.
*lectricity is not an enery resource because it has been enerated usin other
sources of enery.
5ost electricity used in the world is enerated in power stations like the ones shown
in 7@.
+ow electricity is eneratedJ
7. +eat from nuclear fuel or from burnin fossil fuels is used to heat water. 'his
produces hihBpressure steam that makes the blades of a turbine spin.9. 'he turbine is used to turn the enerator.:. 'he enerator enerates electricity.
! renewable enery source is one that will not run out. 2ood is an e-ample of a
renewable source of enery. !s wood is cut down( new fastBrowin trees are
planted to replace those cut down.
ame of enery !dvantaes Disadvantaes+ydroelectric power • 'he water isn,t Lused,
and therefore can be
reused over and over
aain.
•
'he power can becreated 9E/P without
the water runnin out.
• It is a very clean
source of enery as no
reenhouse ases are
created.
• 'hey are very
e-pensive to build and
must be built to hih
standard.
•
'he creation of damscan create Coods and
natural environments
will be destroyed.
• Alacin a damn in front
of a river can cause
neihborin countries
to lack access of water.
Spins
enerato
Drives
turbine
Gsed to
heat
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'idal enery • It can last for a lon
time
• 5aintenance is cheap
• It is ecofriendly as it
doesn,t create
reenhouse ases.
• ;ost of construction is
very hih
• +ih waves can
damae the plant
• Very limited to
locations ofconstructions
2ave enery • 'hey are renewable
because they will
never run out and
waves will always hit
the shore.
• 'hey are easily
predictable and can
show you how much
enery will beproduced.
• It is ecofriendly as it
doesn,t release any
reenhouse ases.
• 'hey can only be built
near cities and very
abundant areas so the
enery can be used
and not wasted.
• %or the enery to be
collected( lare load
machines are needed
which could disturb thehabitat of the sh.
• 'hey are much less
e6cient durin rouh
weather.2ind power • 2ind is free and
therefore renewable
• nce it is built( no
reenhouses or
pollutants are made
• 0emote areas can use
it as a source of enery
• 'he strenth of wind
isn,t constant and the
amount of enery is
therefore also not
constant.
• 'hey are supposedly
loud• 'hey are supposedly
noisySolar power • Sunliht is free so it is
renewable
• It doesn,t create any
pollution
• It can be used in
remote areas to
enerate enery
• Solar enery can only
be harnessed durin
sunny daytimes
• Solar panels are
e-tremely e-pensive
• Fare areas of land are
needed to capture as
much sunliht aspossible
eothermal enery • It is ecofriendly as it
doesn,t release any
reenhouse ases
• 'hey are not weather
reliant
• 'hey are renewable
• nly few sites have the
potential of eothermal
enery
• 'otal enery enerated
is too small
• It is very danerous
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sources of enery because there is the
risk of a volcano
eruptin
+ow this work is in the te-t book paes 7:B7@
SECTION E: So!ids' !i()ids and %ases
Solids are often very dense) they have a hih mass for a certain volume. Fi&uids are
often less dense than solids( and ases have very low densities.
Density = mass/volume
'he volume of an irreular object can be determined by usin a displacement can
and a measurin cylinder. It is easier to cut thins with a sharp knife than a blunt
one( because with a sharp knife all the force is concentrated into a much smaller
area. Aressure is dened as the force per unit area.
Aressure = force/ area
Some applications re&uire a low pressure( such as tractors and camel,s feet as they
are supposed to move over mud and sand and are not supposed to sink.
ases also e-ert pressure around them. 'he pressure e-erted by the atmosphere
on your body is about 7??(??? Aa. !n e-periment to prove this is by usin two lare
bowls. Kou place the two toether and pump the air out. 'he bowls couldn,t be
pulled apart( even when the horses tried. 'his is because when air is inside thespheres( the pressure is the same inside and outside. If the air is sucked out(
pressure is only actin from the outside. 'he hemisphere can,t be pulled apart until
air is let back into them.
Aressure dierence "Aa$ = heiht "m$ - density "k/m:$ - "/k$
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1rownian motion proves that particles in a li&uid or a as have continuous
movement. Aarticles of a li&uid or as are movin around continually and bump into
each other and into tiny particles such as pollen rains.
Aressure = 7/volume. +ere the pressure is inversely proportionally to volume.
1oyles is law) A7V7 = A9V9 this needs a -ed temperature and mass
ases can be compressed because the particles are very spread out. 2hen a as is
s&uashed into a smaller container it presses on the walls of the container with a
reater pressure. If the as is kept at the same temperature( the averae of the
particles stays the same. If the same number of particles is s&uee
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container are harder and happen more often. 'his results in the averae pressure
e-erted by the particles increasin.
2hen we cool a as the kinetic enery of its particles decreases. 'he lower the
temperature of a as the less kinetic enery its particles haveB they move more
slowly. !t absolute
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Kou can see the shape of the manetic eld around a manet by usin iron llins
or a plottin compass. Aut the manet beneath a piece of paper and add sprinkle
iron llins on top. %or the compasses( they will all be facin the South Aole.
'hese manetic lines of forceJ show the shape of the manetic eld( the direction of
the manetic eld and the strenth of the manetic eld as the closer the eld
lines( the stroner the manetic eld.
2hen a current Cows throuh a wire a manetic eld is created around the wire.
'his is called electromanetism. 'he eld around the wire is &uite weak and circular
in shape. 'he direction of the manetic eld depends upon the direction of the
current and can be found usin the rihtBhand rip rule.
'he strenth of the manetic eld around a currentBcarryin wire can be increased
by increasin the current in the wire or wrappin the wire into a coil or solenoid.
'he shape of the manetic eld around a solenoid is the same as that around a bar
manet. 'he positions of the poles can be determined usin the rihtBhand rip
rule.
'he strenth of the eld around a solenoid can be increased byJ increasin the
current Cowin throw throuh the solenoid( increasin the number of turns on the
solenoid and wrappin the solenoid around a manetically soft core such as iron.
'his combination is called an electromanet.
2hen the bell is pressed the circuit is complete and current Cows. 'he soft iron core
of the electromanet becomes maneti
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the iron armature moves( the hammer strikes the bell and at the same time a ap is
created at the contact screw. 'he circuit is incomplete and current stops Cowin.
'he electromanet is now turned o so the sprin,s armature returns to its oriinal
position. 'he circuit is complete and the whole process beins aain.
;ircuit breakers use electromanets to cut o the current if it becomes larer than acertain value. If the current is too hih the electromanet becomes stron enouh
to pull the iron catch out of position so that the contacts open and the circuit
breaks. nce the problem in the circuit has been corrected the catch is repositioned
by pressin the reset button.
2hen lare currents Cow in a circuit there is always daner of the user receivin a
severe electric shock. *ven turnin the circuit on/o is ha
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! voltae is produced when a manet moves in a coil of wire. 'his process is called
electromanetic induction.
It is not practical to enerate lare amounts of electricity by passin a manet in
and out of a coil of wire. Instead( enerators induce a current by spinnin a coil of
wire inside a manetic eld( or by spinnin a manet inside a coil of wire. !s thishappens( a potential dierence is produced between the ends of the coil( which
causes a current to Cow.
ne simple e-ample of a enerator is the bicycle dynamo. 'he dynamo has a wheel
that touches the back tyre. !s the bicycle moves( the wheel turns a manet inside a
coil. 'his induces enouh electricity to run the bicycleRs lihts.
! bicycle dynamo. 'he wheel of the dynamo rubs aainst the bicycle tyre to turn a
manet sited within a coil of wire. 'his enerates electricity to power the bicycleRs
lamps.
'he faster the bicycle moves( the reater the induced voltae B and the brihter the
lihts.
2hen a wire is moved in the manetic eld of a enerator( the movement(
manetic eld and current are all at riht anles to each other. If the wire is moved
in the opposite direction( the induced current also moves in the opposite direction.
0iht hand with thumb( forener and second ner at >? derees with arrows.
'humb shows direction of movement. %orener represents eld. Second ner
shows current from positive to neative.
%leminRs riht hand rule
In a enerator( one side of a coil moves up durin one half turn and then down
durin the ne-t half turn.
'his means that as a coil is rotated in a manetic eld( the induced current reverses
direction every half turn. 'his is called alternatin current "!;$.
It is dierent from the direct current "D;$ produced by a battery B which is always in
the same direction.
;urrent Cows in e-ternal circuit. 1rushes continuous contact between e-ternal
circuit( slip rins. Slip rins connected to coil. ;urrent induced in rotatin coil. 'he
coil rotated in manetic eld.
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;oil motion in an !; enerator
ormally in a enerator( the coil is -ed and mounted outside the manet( and it is
the manet which moves.
'he si
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Vp is the voltae applied to the primary coil in volts
s is the number of turns on the secondary coil
p is the number of turns on the primary coil
! transformer is an electrical device that chanes the voltae of an alternatin
current "!;$ supply( such as the mains electrical supply.
! transformer chanes a hihBvoltae supply into a lowBvoltae one( or vice versaJ
• a transformer that increases the voltae is called a stepBup transformer• a transformer that decreases the voltae is called a stepBdown transformer
'he ational rid
*lectricity is transferred from power stations to consumers throuh the wires and cables of
the ational rid.
2hen a current Cows throuh a wire some enery is lost as heat. 'he hiher the current(
the more heat is lost. 'o reduce these losses( the ational rid transmits electricity at
a low current. 'his needs a hih voltae.
Aower stations produce electricity at 9(??? V. *lectricity is sent throuh the ational rid
cables at E??(??? V( 9P(??? V and 7:9(??? V.
StepBup transformers are used at power stations to produce the very hih voltaes neededto transmit electricity throuh the ational rid power lines. 'hese hih voltaes are too
danerous to use in the home( so stepBdown transformers are used locally to reduce the
voltae to safe levels. 'he voltae of household electricity is about 9:? V.
'he ratio between the voltaes in the coils of a transformer is the same as the ratio of the
number of turns in the coils.
'his relationship can be shown by the followin e&uationJ
'his can also be written asJ
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StepBup transformers have more turns on the secondary coil than they do on the primary
coil.
StepBdown transformers have fewer turns on the secondary coil than they do on the
primary coil.
*lectrical power is calculated by multiplyin voltae "in volts$ by current "in amps$.
If a transformer is 7??N e6cient( then the input power will e&ual the output power. 'his
can be shown in the followin e&uationsJ
Input power = output power
Input "primary$ voltae input "primary$ current = output "secondary$ voltae output
"secondary$ current
VAIA = VSIS
2hereJ
VA is input "primary$ voltae
Ip is input "primary$ current
Vs is output "secondary$ voltae
Is is output "secondary$ current
SECTION G: +adioacti$it" and ,artic!es
!toms are made up of electrons( protons and neutrons. 'he electron is a very liht particle
with very little mass. It has a neative chare. *lectrons orbit the nucleus of the atom. 'he
nucleus is very small compared to the si
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Arotons and neutrons are also called nucleons because they are found in the
nucleus of the atom.
!tomic particle Aarticle mass 0elative chare*lectron 7 B7 neativeAroton 9??? 87 positiveeutron 9??? ? neutral
'he nucleus of an atom is surrounded by electrons. 'he electrons are movin
rapidly around the nucleus in a cloud or shell. !n atom is electrically neutral. 'his is
because the number of positive chares carried by the protons in its nucleus is
balanced by the number of neative chares on the electrons in the electrons in the
electron around the nucleus.
'he chemical behavior and properties of a particular element depend upon how the
atoms combine with other atoms. 'his is determined by the number of electrons in
the atom. 'he atomic number of an element of an element tells us how many
protons each of its atoms contains. %or e-ample( carbon has T protons in its nucleus
B the atomic number of carbon is therefore T. 'he atomic number is sometimes
called the proton number. 'he atomic number is iven the symbol U.
'he total number of protons and neutrons in the nucleus of an atom determines its
atomic mass. 2e refer to the mass of an atom by its mass number of nucleon
number) this number is the total number of protons and neutrons in the atom. 'he
mass number of an element is iven the symbol !.
*ach particular type of atom will have its own atomic number( which identies the
element.
5ass number( ! = number of neutrons 8 number of protons = number of nucleons
umber of neutrons = number of nucleons # number of protons = !B U
'he number of protons in an atom identies the element. 'he chemical behavior of
an element depends on the number of electrons it has which is the same as the
number of protons in the nucleus. 'he number of neutrons in the nucleus can vary
slihtly. !toms of an element with dierent numbers of neutrons are called isotopes
of the element. 'he number of neutrons in in a nucleus aects the mass of the
atom. Dierent isotopes of an element will all have the same atomic number( butdierent mass numbers.
Isotopes of an element have dierent physical properties from other isotopes of the
same element. 'he dierences are the mass and the stability of the nucleus.
'he protons are held in the nucleus by the nuclear force. 'his force is stron enouh
to hold the nucleus toether aainst the electric force repellin the protons away
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from each other( the presence of neutrons in the nucleus aects the balance
between these forces. 'oo many or too few neutrons will make the nucleus unstable.
!n unstable nucleus will eventually decay. 2hen the nucleus of an atom decays it
ives out enery and may also ive out alpha or beta particles.
2hen unstable nuclei decay they ive out ioni
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0adiation Ioni
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beta particle( an electron( has practically no mass so the mass number( !( is the
same in H and K. !s the beta particle has a chare of B7( the atomic number of the
new element is increased to U87.
amma decayJ
amma radiation is hihBenery electromanetic radiation) after an unstable
nucleus has emitted an alpha or beta particle it sometimes has surplus enery. It
emits this enery as amma radiation. amma rays are pure enery( so they do not
have any mass or chare. 2hen a nucleus emits a amma ray there is no chane to
either the atomic number or the mass number of the nucleus.
'he 1ec&uerel is a measure of how many unstable nuclei are disinteratin per
secondB one 1ec&uerel means a rate of one disinteratin per second.
Ahotoraphic lm is still used to detect radioactivity. Scientists that use radioactive
material wear a strip of photoraphic lm in a bade. If the lm becomes foy( it
means that the scientist has been e-posed to a certain amount of radiation. 'hese
bades have to be reularly checked.
'he eierB5uller tube is a tube used to measure the level of radiation. It is a lass
tube with an electrically conductin coatin on the inside surface. 'he tube has a
thin window made of mica. 'he tube is contains a special mi-ture of ases at very
low pressure. In the middle of the tube( electrically insulated from the conductin
coatin( there is an electrode. 'his electrode is connected( via a hih value resistor(
to a hihBvoltae supply( typically :??B?? V.
2hen ioni
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ne form of uranium is a radioactive element that decays very slowly. 'wo of tis
decay products are ases. 'hese are the radioactive ases radon and thoron.
0adonB999 is a hihly radioactive as produced by the decay of radiumB99T. 'horon
or radiumB99? is an isotope of radium formed by the decay of a radioactive isotope
of thorium.
!s these decay products are ases( they seep out of radioactive rocks.
Violent nuclear reactions in stars and e-plodin stars called supernovae produce
very eneretic particles and cosmic rays that continuously bombard the *arth.
Fower enery cosmic rays are iven out by the sun.
'he atoms that make up our bodies contain radioactive atoms that were created
millions of years ao when the solar system was created. 2e also breathe in tiny
amounts of the radioactive isotope of carbonB7E.
2e use articial materials for many purposes. eneratin electricity in nuclear
power stations has been responsible for the leakin of radioactive material into the
environment. 0adioactive tracers are used in industry and medicine. 0adioactive
materials are also used to treat certain forms of cancer. +owever the majority of
radiation is naturalB the amount produced from medical and civil use in industry is
very small indeed.
0adioactive decay is a random process. It is impossible to tell which nuclei will
disinterate at any particular time.
'he radioactive decay raph is an e-ponential decay as it is decreasin
proportionally.
'he halfBlife of a radioactive sample is the averae time taken for half the oriinal
mass of the sample to decay. 'he halfBlife is dierent for dierent radioactive
isotopes.
!fter one halfBlife period( the amount of the oriinal unstable element is halved.
!fter a second period of time( the amount have halved aain.
'o measure the halfBlife of a radioactive material we must measure the activity of
the sample at reular times. 'his is done usin a eierB5uller tube linked to a rate
meter. 1efore takin measurements( we must subtract the backround radiation
from the measurements. 2e then measure the rate of decay of the sample atreular time intervals. 'he rate of decay is shown by the count rate on the rate
meter. Isotopes with shortBlives are suited to medical use. 'his is because the
activity of a source will rapidly become very small as the isotope decays &uickly.
0adioactive isotopes are used as tracers to help doctors identify diseased orans. !
radioactive tracer is a chemical compound that emits amma radiation. 'he tracer
is taken in orally or injected. Its passae around the body can then be traced usin
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amma ray camera. ! short halfBlive is important as this means that the activity of
the tracer decreases to a very low level in a few days. !n e-ample of this is iodineB
79: which is absorbed by the thyroid land.
ther isotopes are used to imae specic parts of the body. %or e-ample the
technetiumB>> is used in medical imain. It is used to help identify medicalproblems that aect many parts of the body.
0adiation from isotopes can have various eects of the cells that make up or bodies.
Fow doses of radiation may have no lastin eect. +iher doses may cause the
normal function of cells to be chaned. 'his can lead to abnormal rowth and
cancer. Very hih doses will kill livin cells.
;ancer can be treated by surery that involves cuttin out cancerous cells. !nother
way of treatin cancer is to kill the cancer cells inside the body. 'his is done with
chemicals containin radioactive isotopes. Gnfortunately( both the cancerous and
the livin cells die. 'o reduce the damae to healthy tissue( chemicals are used to
directly taret the location of the cancer in the body. 'hey may emit either alpha or
beta radiation. 1oth types of radiation have a short rane in the body so they only
aect a small volume of tissue close to the taret. 'he radioisotope iodineB7:7 is
used in the treatment of various diseases of the thyroid land. It has a halfBlife of
about eiht days and decays by beta particle emission.
Ioni
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dust miht cause false readins with an optical auin system. ;oal dust is much
less dense than coal so the amma ray system still works properly. !nother
e-ample of auin uses a similar process to monitor the thickness of plastic
sheetin and lm. 'he thicker the sheet( the reater the amount of radiation it
absorbs. 1y monitorin the amount of radiation( the thickness of the sheetin can
be closely controlled durin manufacture.
'racin and measurin the Cow of li&uids and asesJ radioisotopes are used to track
the Cow of Cuids in industrial processes. Very tiny amounts of radiation can easily
be detected. ;omple- pipin systems( like heat e-chaners in power stations( can
be monitored for leaks. 0adioactive tracers are even used to measure the rate of
dispersal of sewae.
0adiocarbon datin is used to nd the ae of oranic matter such as trees and
animals.
0adiocarbon datin measures the level of an isotope called carbonB7E. 'his is made
in the atmosphere. ;osmic rays from space are continually rainin down upon the
*arth. 'hese have a lot of enery. 2hen they strike atoms of as in the upper layers
of the atmosphere( the nuclei of the atoms break apart. 'he parts Cy o at hih
speed. If they strike over other atoms they can cause nuclear transformations to
take place. 'hese transformations turn the elements in the air into dierent
isotopes. ne such collision involves a fastBmovin neutron strikin an atom of
nitroen. 'he nuclear e&uation for this process isJ
7E(P 8 7(?n B 7E(T ; 8 7(7p
7( ? n represents a neutron. 7(7p represents a proton.
'he result of the collision of a neutron with a nitroen atom is a nuclear
transformation. 'he nitroen atom is transformed into an atom of the radioactive
isotope of carbon( carbonB7E. ;arbonB7E also reacts with o-yen in the atmosphere
to form carbon dio-ide which is then absorbed by plants in the process of
photosynthesis. 'he animals then eat the plant and it is now in a food chain. 'hese
carbonB7E atoms will decay( but in livin plants and animals( they are continuously
replaced by new ones.
2hen a livin oranism dies( the replacement process stops. !s time passes( the
radioactive carbon decays and the proportion of radioactive carbon in the remains
of the plant or animal( compared with the stable carbon isotope( decreases.
'here are limitations to the method of radiocarbon datin. It assumes the level of
cosmic radiation reachin the *arth is constant( which is not necessarily an accurate
assumption. %ortunately( the techni&ue has been calibrated to take the variations of
cosmic ray activity into account. 'his is done by testin samples of a known ae(
kike material from the mummies of *yptian Aharaohs. 'he radiocarbon method is
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not used to date samples older than ?(???BT?(??? years because( after 7? halfB
lives the amount of carbonB7E remainin in samples is too small to measure
accurately.
In oranic( nonBlivin matter doesn,t absorb carbonB7E( so dierent techni&ues must
be used for ndin out the ae of rocks and minerals. 2hen a radioactivesubstance decays it transforms into a dierent isotope( sometimes of the same
element( sometimes a dierent element. 'he oriinal radioisotope is called the
parent nuclide and the product is called the dauhter nuclide. 5any of the products
of decay( the dauhter isotopes( are also unstable and these too decay. 'his means
that as the parent isotope decays its breeds a whole family of elements in what i
called a decay series. 'he end of the decay series is a stable isotope.
'he table shows some radioactive parent isotopes with the stable dauhters formed
at the end of their particular decay series.
0adioactive parent isotope Stable dauhter element +alfBlife "years$AotassiumBE? !ronBE? 7.9 billion 'horiumB9:9 FeadB9?@ 7E billionGraniumB9: FeadB9?P P?E billionGraniumB9:@ FeadB9?T E.EP billion;arbonB7E itroenB7E T@
Ioni
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In all cases( the loner the period of e-posure to radiation the reater the risk of
serious cell damae. 2orkers in the nuclear industry wear bades to indicate their
level of e-posure. Some are strips of photoraphic lm that become increasinly
Lfoy, as the radiation e-posure increases. !nother type of bade uses a property
called thermoluminescence. 'hermoluminescence means that the e-posed material
will ive out liht when it is warmed. 'he radiation releases enery to make heat sothe thermoluminescencent bades ive out more liht when e-posed to hiher
levels of radiation.
Arecautions that must be followed to safely handle radioactive materialsJ
'he samples are stored in lead containers to block even the most penetratin form
of radiation( amma rays. 'he containers are clearly labeled and must be stored in
a locked metal cabinet. 'he samples are handled usin tons and are kept as far
from the body as possible. In nuclear industry and research laboratories( much
larer amounts of radioactive material are used. 'hese have to be handled with
reat care. Very eneretic sources will be handled remotely by operators who areshielded by lead( concrete and thick lass viewin panels.
'he major problem with nuclear materials is lonBterm storae. Some materials
have e-tremely lon halfBlives so they remain active for thousands and sometimes
tens of thousands of years. uclear waste must be stored in sealed containers that
must be capable of containin the radioactivity for enormously lon periods of time.
Dalton thouht that the atom is a solid sphere.
M.M. 'hompson thouht that atoms were positively chared spheres with neatively
chared electrons embedded into them.
*rnest 0utherford red alpha particles at very thin old foil. !lpha particles are
positively chared particles iven o by some
radioactive substances.
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'he
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'he framents of this decay are two dauhter nuclei of bariumB7EE and kryptonB@>.
'he decay also produces amma radiation and three more neutrons. 'he e&uation
for this decay isJ
'he ssion reaction produces a hue amount of enery. 'his is because some of the
mass of the oriinal uraniumB9:T nuclei is converted to enery. 5ost of the enery
is carried away as the kinetic enery of the two lihter nuclei. Some is emitted as
amma radiation. 'he three neutrons produced by ssion may hit other nuclei of
uraniumB9: and therefore causin the process to repeat. If one neutron from each
ssion causes on nearby uraniumB9: to split( then the ssion reaction will keepoin.
'his is called a chain reaction. If this reaction is allowed to take place in an
uncontrolled way( the result is a nuclear e-plosion. 'his involves the sudden release
of enormous amounts of heat enery and radiation. In a nuclear reactor the process
is controlled so that heat enery is released over a lon period of time. 'he heatproduced in the core or heart of the reactor is used heat water. 'he steam produced
then drives turbines to turn enerators.
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'he reactor core
contains fuel rods of enriched uranium. *nriched uranium is uraniumB9:@ with a
hiher proportion of uraniumB9: than is found in natural reserves of uranium.
'he job of the moderator is to absorb some of the kinetic enery of the neutrons to
slow them down. 'his is because slow neutrons are more easily absorbed by
uraniumB9:. 'he slowin of neutrons therefore starts the ssion process.
In the nuclear reactor there are also control rods( made of boron or cadmium. 'hese
absorb the neutrons and take them out of the ssion process completely.
'he waste products present a serious damae for lonBterm storae. 'hey are
usually stored in contains that are buried under round. 'he rocks must be
impermeable to water and the eoloy of the site and must be stable. 'heyshouldn,t be placed in areas such as earth&uake
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