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National 5 Physics Properties of Matter Summary Notes &
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Page 1: broughtonphysics.files.wordpress.com€¦  · Web viewSpecific Heat capacity: Changing Temperature. The temperature of a substance can be changed by supplying it with energy or removing

National 5 Physics

Properties of MatterSummary Notes

&Homework

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National 5 Physics Summary Notes Electricity & Energy

HeatHeat Energy

Heat is a form of energy. Heat energy can be produced from another form of energy or changed into another form, for example:

- kinetic energy → heat energy (through friction)- electrical energy → heat energy (in a resistor)

- heat energy → electrical energy (thermocouple)

As it is a form of energy heat is measured in Joules, J.

Temperature

Temperature is a measure of the mean kinetic energy of the particles of a substance. This means that as the temperature of a substance increases, the kinetic energy (and therefore the speed) of the particles in that substance increases too.

Temperature is measured in degrees Celsius, °C. Temperature can also be measured in Kelvin, K, (see Gas Law and Pressure).

Specific Heat capacity: Changing Temperature

The temperature of a substance can be changed by supplying it with energy or removing energy from the substance (heating or cooling it). The temperature change depends on the energy supplied, the mass of the substance being heated and the material itself.

Different materials have different specific heat capacities. This is the energy required for 1kg of a substance to achieve a temperature change of 1°C.

EH=cm ΔT

EH - energy supplied/removed Jc - specific heat capacity J kg-1 °C-1

m - mass of the substance kgΔT - temperature change °C

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States of Matter

There are 3 states of matter, solid, liquid and gas. A substance can change between states if it receives or loses energy.

Changes of State

Increasing energy solid → liquid meltingliquid → gas evaporating

Decreasing energy gas → liquid condensationliquid → solid freezing

Changing state also requires an increase or decrease in energy. When a substance is changing state it does not experience a change in temperature.Cooling graph of a substance

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Specific Latent Heat of Fusion (solid ↔ liquid)

Energy is required to change the state of a substance from a solid to a liquid. The energy required depends on the mass of the substance and the substance itself. The property of the substance is known as specific latent heat of fusion.

EH=ml fEH - energy supplied/removed Jm - mass of the substance kglf - specific latent heat of fusion J kg-1

Specific Latent Heat of Vaporisation (liquid ↔ gas)

Energy is required to change the state of a substance from a liquid to a gas. The energy required depends on the mass of the substance and the substance itself. The property of the substance is known as specific latent heat of vaporisation.

EH=mlvEH - energy supplied/removed Jm - mass of the substance kglv - specific latent heat of vaporisation J kg-1

Heat Transfer

Heat energy can be transferred by three methods:

Conduction - The vibrations of the hot particles are passed to their neighbours. This takes place in solids.

Convection - Hot liquids or gases are less dense than colds ones and so they will rise and the cold gases and liquids will fall. This sets up a convection current. This takes place in liquids or gases.

Radiation - A form of electromagnetic radiation (infrared) Energy is transferred as rays. This is the only method by which heat can be transferred through a vacuum.

The greater the temperature difference the greater the rate of heat transfer.

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Heat Loss

Heat always moves from hot objects to cold objects. The rate of heat loss depends on the temperature difference between the two objects.

Reducing Heat Loss

Heat loss from the home can be reduced in the following ways:

Loft insulation - Reduces heat loss through by conduction through the ceiling.

Double Glazing - A vacuum between the panes of glass reduces heat loss by conduction.

Draught Excluders - Reduce heat loss by convection.

Foil-backed Plasterboard - Reduces heat loss by radiation from the walls.

Foil-backed Radiators - Reflects heat back into room and so reduces heat loss by radiation.

Cavity Wall Insulation - A foam filling between the walls prevents heat loss due to convection or conduction.

Carpets - Reduces heat loss by conduction through floor.

PressureDefining Pressure

Pressure is defined as the force exerted per unit area by one medium on another. This includes solids, liquids and gases. That's right, gases exert pressure too.

Calculating pressure

Pressure=ForceArea

Pressure is measured in pascals (Pa) or newtons per square metre (N m-1)Force is measured in newtons (N)Area is measured in square metres (m2)

1 pascal = 1 newton per square metre

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Comparing Pressures

Pressure allows us to compare the effect that 2 very different objects may have on their surroundings.

Take the example of an elephant and the stiletto heel of a shoe. Which would you rather have step on your foot?

Elephant StilettoForce exerted by elephant Force exerted by stilettoForce is weight so: Force is weight so:W=mg=7000×9 .8=68 600 N

W=mg=50×9 . 8=490 N

Area of elephants foot ~0.2m2 Area of stiletto heel ~0.0001m2

P=FA

=68 6000. 2

=343 000 Pa

P=FA

=4900.0001

=4 900 000 Pa

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Gas LawsKinetic Model of a Gas

Physicists often use models to describe situations that are difficult to visualise. This includes the very large and the very small. The kinetic model of a gas describes the motion of the particles in the gas and uses their behaviour to explain our observations of the gas itself.

There are 3 important quantities about the gas that we can observe, which can be explained by visualising the particles within the gas.

Volume - The volume of a gas is the 3 dimensional space the gas occupies. This space is usually determined by the container that the gas is in. We do not concern ourselves with the volume of the particles, only the volume of the gas as a whole.

Temperature - The temperature of a gas is a measure of the average kinetic energy of the particles in that gas. The greater the temperature, the greater the average kinetic energy of the particles and therefore the greater their speed. (Note that it is the temperature of the gas and the speed of the particles!)

Pressure - The pressure of the gas is caused by the particles colliding with the walls of the container. The more frequent or violent the collisions, the more force is exerted on the walls of the container and therefore the greater the pressure.

Relationship between Volume and Pressure of a Gas

For a fixed mass of gas at a constant temperature, the pressure of a gas is inversely proportional to its volume:

P∝ 1V P×V=constant P1V 1=P2V 2

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Relationship between Pressure and Temperature of a Gas

For a fixed mass of gas at a constant volume, the pressure of a gas increases as the temperature increases:

This is not a proportional relationship, as the line does not go through the origin. If we extend the graph into the negative temperature scale we see the following:

This is where we introduce the kelvin scale. -273°C is now equivalent to zero kelvin

We find that pressure is directly proportional to temperature, when temperature is measured in kelvin.

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0

0

0

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P∝TPT

=constantP1

T1=P2

T2

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Converting between Celsius and Kelvin

To convert between the two temperature scales we either add or subtract 273:

Convert: °C to K add 273K to °C subtract 273

Relationship between Volume and Temperature of a Gas

For a fixed mass of gas at a constant pressure, the volume of a gas is directly proportional to its temperature, when measured in kelvin:

V∝TVT

=constantV 1

T 1=V 2

T 2

General Gas Equation

All three gas laws combine to form the general gas equation:

PVT

=constantP1V 1

T 1=P2V 2

T 2

Remember: temperatures must be converted to kelvin to work in this equation!

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Homework 1 Specific Heat CapacityMaterial Specific heat capacity in J/kg oCAluminium 902Copper 386Glass 500Glycerol 2 400Water 4 180

1. What is the difference between heat and temperature?

2. What is meant by the following statement:“The specific heat capacity of water is 4180 J / kg °C.”

3. Calculate the missing entries in this table. DO NOT COPY THE TABLE.

Heat Energy / J Specific Heat Capacity / J / kg °C Mass / kg

Change in Temperature /

°C

(a) 36 900 4.5 2

(b) 10 080 2100 12

(c) 105 600 480 40

(d) 2400 128 2.5

4. A 2.4 kg lump of brass is heated up by a Bunsen burner. When 9120 J of heat energy has been absorbed, the temperature of the brass increases by 10 °C. What is the specific heat capacity of the brass?

5. A pane of glass has a mass of 800 g. What is the temperature

change of the glass if it is heated by 1000 J of heat energy?

6. A block of lead is heated from 24 °C to 28°C by a heat source that gives off 6144 J of heat energy. What is the mass of the lead block? (Specific heat capacity for lead is 128Jkg-1oC-1)

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7. In an experiment, a 2 kg block of copper is warmed with a 70 W electrical immersion heater. The temperature of the copper is measured every minute using a thermometer. The heat energy used is calculated by finding the power of the heater and using E = P t. The results are shown.

Heat Energy / J Change In Temperature / °C

0 0

4 200 3.4

8 400 6.8

12 600 10.2

16 800 13.6

21 000 17.0

(a) Using this data, draw a line graph and use the gradient of the straight line to find the specific heat capacity of copper.

(b) Is this experimental value for the specific heat capacity of copper larger, smaller or the same as the actual value? Explain any difference.

Homework 2 Latent Heat

1. a) Which takes more heat, melting ice or evaporating water?b) Which process requires the least amount of heat energy?

Substance Heat of Fusion(J/kg)

Heat of Vaporization(J/kg)

water 3.3 x 105 2.3 x 106

alcohol (ethyl) 1.4 x 104 8.5 x 105

alcohol (methyl) 6.8 x 104 1.1 x 105

gold 6.3 x 104 1.6 x 105

lead 2.5 x 104 8.7 x 105

mercury 1.2 x 104 2.7 x 105

silver 8.8 x 104 2.4 x 106

nitrogen 2.5 x 104 2.0 x 105

oxygen 1.4 x 104 2.1 x 105

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Copper

HeaterThermometer

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2. How much heat is given off when 3.2 kg of water freeze? Assume the temperature stays constant at 0oC.

3. How much heat is required to change 2.5 kg of water at 100oC to steam at 100oC?

4. How much heat is needed to change 2.0 kg of silver at 20oC into liquid silver? Silver melts at 961oC. Specific heat capacity is 233J/kgoC

8. Use your knowledge of physics to comment on this cartoon.

Homework 3 Pressure1. What is the meaning of the term ‘pressure’ in terms of force and area?

2. Calculate the missing numbers in this table. DO NOT COPY THE TABLE.

Pressure / Pa Force / N Area / m2

(a) 4000 0.5

(b) 9000 8.0 x 10-2

(c) 12 000 7.2 x 105

3. A 480 g tin of baked beans is a cylinder with a radius of 3.2 cm. It is placed on a kitchen counter. What is the pressure on the counter caused by the tin?

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4. A car of mass 1250 kg is driven on to a bridge. The pressure on the surface of the bridge when all four tyres are on the ground is 39.0 kPa. What is the contact area of one tyre on the bridge?

5. A television has a length of 124 cm, a height of 93 cm and a depth of 7.0 cm.

If it has a mass of 30 kg, what is the:

(a) Maximum pressure that the television can exert on a surface?

(b) Minimum pressure that the television can exert on a surface?

6. Are you more likely to fall through an icy lake if you are on your tip toes or lying flat on your back with your arms and legs stretched out? Explain your answer.

Homework 4 Gas Laws I1. Explain, using the kinetic theory of particles, what happens to the

particles in a liquid when it evaporates and becomes a gas.

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7.0 cm

93 cm

124 cm

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2. Explain, using kinetic theory, how the air in a bicycle tyre creates pressure on the inside surface of the tyre.

3. Why does the Kelvin temperature scale start at -273 °C?

1. A flask is sealed with air inside, and is placed in a heat bath. The temperature of the gas increases from 20 °C to 70°C. After every 10 °C temperature increase, the pressure of the gas is measured using a Bourdon gauge. The results are shown.

(a) Sketch a rough graph (no values required just the shape) of pressure against temperature (in degrees Celsius).

(b) Sketch a rough graph (no values required just the shape) of pressure against temperature (in Kelvin).

(c) What do these two graphs tell you about the relationship between the pressure and temperature of a fixed mass of gas?

(d) Explain this relationship in terms of the kinetic theory of particles.

2. Explain, using the appropriate gas law, why it is important that car tyres are not filled up with so much air that the air pressure is above the car manufacturer’s guidelines?

3. At a temperature of 20 °C, the pressure of a fixed mass of gas in a sealed container is found to be 104 kPa. The gas is heated to a uniform temperature of 90 °C using a heat bath.

What is the pressure of the gas at a temperature of 90 °C?

4. The pressure of the air in a lorry tyre is found to be 2.58 x 105 Pa at the end of a journey.

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Air

Heat Bath

Thermometer

Bourdon Gauge Temperature /

°C Pressure / x 105 Pa

20 1.01

30 1.04

40 1.08

50 1.11

60 1.15

70 1.18

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Once the tyre has cooled down, the temperature of the air inside the tyre is found to be 10 °C with the pressure decreasing to 2.41 x 105 Pa.

What was the temperature of the air in the tyre at the end of the journey? Give your answer in degrees Celsius.

Homework 5 Gas Laws II

1. In an experiment, the volume of a fixed mass of gas is decreased by trapping the gas at the top of a glass tube with a quantity of oil and then using a pump to push the oil up the tube. The pressure of the gas is measured with a Bourdon gauge and the volume of gas is measured using a calibrated scale next to the glass tube. The results are shown.

(a) Sketch a rough graph (no values needed) of volume against 1 / pressure.

(b) What does this graph tell you about the relationship between the volume and pressure of a fixed mass of gas?

(c) Explain this relationship in terms of the kinetic theory of particles.

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Oil

Bourdon Gauge

Fixed Mass of Gas

Pump

Pressure / x 105 Pa1.5 1.57

1.6 1.48

1.7 1.39

1.8 1.31

1.9 1.24

2.0 1.18

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2. Explain, using the appropriate gas law, why a balloon will burst if you squeeze it.

3. A 5 cm3 syringe is filled with air and the pressure of the air is found to be 1.01 x 105 Pa. The syringe plunger is then pushed until there is 3 cm3 of air. What is the new air pressure?

4. A scuba diving air tank has a volume of 7.5 litres and is filled with air at a pressure of 1.21 x 107 Pa. What volume of air will be released by the tank at atmospheric pressure (1.01 x 105

Pa)?

Homework 7 Gas Laws III1. In an experiment, an open capillary tube with a mercury thread is

placed in to a heat bath.

As the temperature of the gas increases, the mercury thread moves up the capillary tube. The pressure of the gas remains constant because the capillary tube is open.The temperature of the gas is measured with a thermometer and the volume of the gas is measured using a scale next to the open capillary tube. The results of the experiment are shown.

(a) Draw a graph of volume against temperature.

(b) What do these two graphs tell you about the relationship between the volume and temperature of a fixed mass of gas?

(c) Explain this relationship in terms of the kinetic theory of particles.

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Mercury Thread

Heat Bath

Thermometer

Open Capillary

Tube

Temperature / K Volume / cm3

20 1.50

25 1.88

30 2.25

35 2.63

40 3.00

45 3.38

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2. The volume of a fixed mass of gas is 30.0 cm3 at 30 °C. The temperature of the gas is increased to 60 °C without changing the pressure.A student makes this statement:

‘As the temperature of the gas has doubled, the volume of the gas will also double. Therefore, the volume of the gas at 60 °C will be 60.0 cm3.’

(a) Explain why this statement is incorrect.

(b)Calculate what the volume of the gas would actually be at 60 °C.

3. Air is trapped in a glass capillary tube by a bead of mercury. The volume of air is found to be 0.15 cm3 at a temperature of 27 °C.

Assuming that the pressure of the air remains constant, what is the volume of the air at a temperature of 87 °C?

4. A fixed mass of gas is trapped in to a syringe. The gas has a pressure of 1.63 x 105 Pa when it has a volume of 3.0 cm3

and a temperature of 22 °C.The gas is then heated until it has a uniform temperature of 57 °C.

What will be the pressure of the gas if the volume of the gas is increased to 5.0 cm3?

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