Additional Notes

CAPACITORS

time Voltage Vs Capacitors are devices which can store charge. This charge can be used later.

Capacitance is measured in FARADS (F).

Capacitors can be used with resistors in series as a timing device.

Capacitors and resistors, connected in series as a potential divider, can be placed with a transistor to act as a time delay switch (eg used at Pelican Crossings). Capacitors are analogue devices because they can have any value between 0V and the supply voltage Vs.

When a capacitor is being charged, the capacitor charges rapidly at first, but then charges more slowly as it fills with charge. Charging stops when the p.d. (voltage) across the capacitor equals the p.d. of the supply voltage.

Symbol:

Use:	capacitors store charge

Connect to:	a resistor

Practical application:	with a resistor a capacitor can be used in a time delay circuit.

The time to charge depends on the size of the capacitor and the size of the resistor in series with the capacitor. The greater the resistance the longer the charging time, the greater the value of the capacitor the longer the time it takes to charge.

When a capacitor is connected up the voltage across the capacitor increases until it reaches the value of the supply voltage (Vs)

THE BIGGER THE VALUE OF THE RESISTANCE AND THE BIGGER THE VALUE OF THE CAPACITOR, THE LONGER IT TAKES TO CHARGE TO Vs

LED’s

LED’s (light emitting diodes) are made from semiconductor materials which emit light when charge flows through them.

LED’s, like other diodes, only conduct electricity when they are connected one way round, but LED’s emit light when they conduct electricity.

+ve -ve flow of electrons If an LED is placed in the circuit the other way round it will not light.

A RESISTOR MUST BE PLACED IN SERIES TO LIMIT THE CURRENT TO ABOUT 10 mA, OR REDUCE THE VOLTAGE ACROSS THE LED OTHERWISE THE LED WILL BE DESTROYED.

eg. The voltage drop across an LED should not exceed 2 V and the maximum current should be 10 mA. If the LED is to be used on a 5 V supply the value of the series resistor, R, can be calculated.

Now find R. Remember in series, I1 = I2 = I3

If ILED = 10 mA then IR must = 10 mA = 0.01 A

VLED

An LED can carry a current of 10 mA and has a voltage drop across it of 2 V.

+ - 12 V What is the size of the resistor that must be placed in series if placed in a circuit with a 12 V supply?

+ - 12 V VLED

Draw a diagram showing how an LED can be operated from a 12 V battery

Calculate the size of the resistor needed in the circuit if the LED operates at 1·8 V, 15 mA

Efficiency

NB The magic triangle ONLY works in this case if the efficiency is put in as a decimal!

Remember that efficiency is a fraction, and an efficiency of 0.75 can also be written as 75%.

Note since there will always be energy loss, it is impossible to obtain an efficiency greater or equal to 100%.

(A solution giving an answer greater than 100% means that the output and input energies have been substituted incorrectly).

Example 1

A coal fired power station has a power output of 200 MW. The power produced by the boiler is 340 MW. Calculate the efficiency of the power station.

Efficiency =x100% = x100% = 59%

Example 2

A crane which is 40% efficient lifts a crate giving it 300 J of potential energy. How much energy must be supplied to the crane to produce this output?

Efficiency =x100%

40 % = x100%

Energy In = x100%

Energy In = 750 MW

Questions

It takes 4500 J to lift a person from the ground floor to the top floor of the school. The lift however uses 90000 J to move a passenger the same distance. What is its efficiency?

5%

A fork lift truck has an efficiency of 50%. If it takes 500 J to lift a box directly, how much energy will be used by the truck to do the same job.

1000J

A tractor has an efficiency of 20%, and uses 600 MJ of energy when ploughing a furrow. How much work has it actually done?

3000 MJ

A light bulb has a power of 60 W but only produces 3 W of light. What is its efficiency?

5%

A low energy light bulb has an efficiency of 20%. How much light will be produced by an 11W low energy light bulb?

2.2 W

A pump is used to lift 23 kg of water through a height of 3 m in 120 seconds. The pump is operated by an electric motor, which uses a current of 2 A from a 12 V supply.

What is the weight of the water? 230 N

How much work is done lifting the water? 230 x 3= 690 J

What power is used to lift the water? 690/120 =5.75 W

What power is given to the motor by the supply? 12 x 2=24 W

What is the efficiency of the system? 24%

Electric charge

You may have investigated static electricity before in a number of ways.

Rubbing a balloon on your clothing and ‘sticking’ it to a wall.

Using a Van de Graaff generator.

Getting a shock getting out of a car.

It is thought that the Greeks were the first to investigate electricity. The philosopher Thales of Miletus noted around 600 BC that pieces of amber could attract light objects after being rubbed. The word electricity itself comes from ēlektron, the Greek word for amber.

There are two types of electric charge, positive and negative.

Through experimentation it is found that like charges repel and unlike charges attract.

Everything you can see and touch is made from atoms. Atoms are made up of three types of particles:

Protons which have a positive charge

Neutrons which have no charge

Electrons which have a negative charge

Atoms have equal numbers of protons and electrons, which causes the atom to be neutral (no overall charge). However, charged items can still pick up small items.

A rod can be charged by rubbing. When brought close to a neutral item, this can cause the charges to be rearranged to give an imbalance on each side.

1. 2. 3.

+ + + + - - - - + + + + - - - -

+ + + + - - - -

The charges on the piece of paper are evenly distributed amongst the piece of paper.

When the negatively charged rod is brought near, the positive charges are attracted and the negative charges repelled.

This imbalance of charge allows the rod to pick up the piece of paper.

When a material is charged by rubbing only the electrons from the atoms are moved.

Depending on the materials used, the rod can either gain electrons and become negatively charged, or lose electrons and become positively charged.

Similarly to the presence of a magnetic field around a magnet, an electric field exists around electrical charge.

The field lines point in the direction that a lone positive charge would move.

Experiment

Investigate charged polythene and acetate rods.

Collect two polythene and two acetate rods, two watch glasses.

Use the apparatus to investigate if the charged rods attract or repel each other.

or

Make a short note to record your results, you will use this information later.

How many different types of charge are there?

What are the different types called?

There are three different particles that make up an atom. Use an appropriate format to present information about these particles.

Present the results you obtained from the experiment in a appropriate way.

Explain how a charged rod can pick up a light neutral object. Diagrams may be useful to assist you.

You may have noticed that the hair of someone in contact with a Van de Graaf generator often sticks out on end. Using your knowledge of electrical charges, give an explanation for why this should happen.

Using your knowledge of the structure of an atom, give a reason why electrons and not protons can be removed from a material by rubbing.

Electric Fields

hen a charge is in an electric field it will experience a force. This is similar to the way that a mass will experience a force in a gravitational field.

The difference is that there are two types of charge so the force in an electric field can be attractive

or repulsive.

Gravitational force is always attractive. You always fall down!

An electric field exists around any charged object. An electric field will also exist between two metal plates connected to an electrical potential. The field lines point in the direction that a positive charge would experience a force.

+500V 0V + - F F

If a charged object is placed in the field then the direction it moves will depend on the sign of the charge. ( +ve or –ve)

The greater the potential difference between the plates the greater the energy gained by any charge.

Potential difference (voltage) is a measure of the energy gained by charge moving across that potential difference.

+ - EW = QV

EW = Energy supplied to charge (J)

Q = Charge (C)

+ -

+ + + + + + + + + + + + - F + + + + + + + + + + + + F

1. When will a charged object experience a force?

+ 2. Draw a diagram to show the shape of the electric field caused by

A positive point charge

-

A negative point charge

+ +

Two positive point charges

- -

Two negative point charges

- +

A positive and negative point charge

Two parallel plates of opposite charge.

3. Write a sentence to link energy gained by a charge and potential difference.

4. What is meant by a potential difference of 6 volts?

PRESSURE

The force (in this case weight) is spread over a large area. This isn’t too painful. Why?

Because the pressure is small.

The force in this example is the same but no sensible person would let you push down. Why?

Because the pressure is concentrated over a very small area. i.e. the pressure is large.

When F acts at 90o to the surface i.e. NORMAL to the surface.

Units: N m-2

This is given the special name of Pascals (Pa)

1 Pa = 1 N m-2

Measuring Pressure

Pressure is measured using a BOURDON GAUGE.

Blow here (force air in) and the party tooter unravels. It works a bit like a party tooter.

The Bourdon gauge works in a similar way. the flattened tube is made of metal with a pointer on the side. as the pressure increases the coil unravels (but only a little bit) and the pointer moves.

The Bourdon gauge does NOT read zero when left in a room. It would read ATMOSPHERIC PRESSURE (approximately 1 atmosphere = 105 Pa)

Put this into your calculator as 1exp5

If the force is not acting along the normal, take the component along the normal before calculating pressure.

Force, F F cos

PRESSURE AND DIRECTION

Bourdon Gauge Thistle Funnel

Place the thistle funnel in various directions at the SAME DEPTH IN THE FLUID. Read the pressure from the Bourdon Gauge.

PRESSURE REMAINS CONSTANT

So, for a given depth of fluid, P = constant.

Therefore, PRESSURE ACTS EQUALLY IN ALL DIRECTIONS.

KINETIC THEORY

All particles are moving.

Pressure is caused when the particles collide with the container walls

The hotter the particles the faster they move

The faster they move the more often and more violent the collisions with the walls, greater impulse therefore greater force.

If the volume is less they will collide more often as there is a shorter distance between the container walls

A few common explanations

For a FIXED MASS OF GAS at CONSTANT TEMPERATURE pressure is inversely proportional to the volume P1V1 = k

For a FIXED MASS OF GAS at CONSTANT PRESSURE temperature (Kelvin) is proportional to the volume V1 / T(K)1 = k

For a FIXED MASS OF GAS at CONSTANT VOLUME temperature (Kelvin) is proportional to the pressure P1 / T(K)1 = k

KINETIC THEORY OF GASES

This model is based on the following assumptions:

ALL GASES ARE MADE UP OF DISTINCT PARTICLES

THE PARTICLES COLLIDE WITH EACH OTHER AND WITH THE WALLS OF THE CONTAINER

There is a large number of particles in a container

The particles move in random directions

The particles have a range of speeds

The actual volume of the particles is negligible compared with the

volume of the container

All collisions are perfectly elastic

Particles do not exert forces on each other except during collisions

he time of contact spent by the particles is negligible

The particles obey Newton’s Laws.

KINETIC THEORY

NB This is a PANTS! Drawing as the molecules are WAY TOO BIG- but you get the idea!

The particle collides with the walls of the container and alters its velocity. If the collision is elastic, how is the velocity changed?

The impulse is equal to the change in momentum.

It is the force of the collision that causes the pressure.

The forces and area are very small, but it is the extremely large number of particles that causes the high pressure.

Explanation of Pressure Law

KINETIC THEORY

The basic assumption of the kinetic theory is that “ALL MATTER CONSISTS OF MOVING PARTICLES”.

BROWNIAN MOTION APPARATUS Evidence of this was discovered by Robert Brown in 1827.

Explanation

The first accurate explanation of this phenomenon was by Albert Einstein in 1905. According to the Kinetic Theory the air particles that are around the much larger ash particles are moving randomly and they keep colliding with each other.

Despite the much larger size of the ash molecules they are still affected by the collisions with the air particles.

The randomly occurring collisions produce unbalanced forces which cause the ash molecules to move and hence explain the random paths seen.

According to the KINETIC THEORY at higher temperatures the particles have more kinetic energy and are therefore moving faster. This means the collisions are more violent and so the specks of ash are jostled around faster.

So how does this explain PRESSURE?

Pressure is caused by the gas molecules striking the container walls. The pressure on a container remains constant suggesting that there is a very large number of molecules hitting the container walls at any time, so there must be a huge number of molecules in the container.

Do our results fit in with this?

As temperature increases the kinetic energy increases so as each particle is moving faster it will collide with the container wall more frequently and with greater force. Thus the pressure increases.

What happens when pressure is zero?

Our theory would suggest that there is NO pressure on the container because no collisions occur with the walls of the container. For this to happen the particles would have no kinetic energy and therefore not be moving.

The temperature at which this occurs is ABSOLUTE ZERO (0 K, -273.15 oC).

Pressure Law

Temperature (oC)	0	20	50	80	100
Temperature (K)	273	293	323	353	373
Pressure (kPa)	93	100	110	120	127

For a fixed mass of gas at constant volume, pressure is directly proportional to temperature measured in KELVIN (K).

The Kelvin Temperature Scale

oC K 100 0 -273.15 373 273 0 Absolute zero

to change oC to K ADD 273.

to change K to oC SUBTRACT 273.

THE GAS LAWS

Pressure Law

P T(K) (at constant V)

For a fixed mass of gas at constant volume, the pressure is directly proportional to absolute temperature (temperature in Kelvin).

Boyle’s Law

P 1/V (at constant T)

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

Charles’ Law

V T(K) (at constant P)

For a fixed mass of gas at constant pressure, the volume is directly proportional to absolute temperature (temperature in Kelvin).

Combined Gas Equation

For each of the set of results below

Plot the raw data and notice the shape of the graph formed

Plot the data that would allow you to show a relation

Use the data provided to show the relationship

Pressure Law

Temperature (oC)	-78	0	20	50	80	100
Temperature (K)	273	293	323	353	373
Pressure (kPa)	67	93	100	110	120	127
Use this to show a relationship!

Charles’ Law

Temperature (oC)	0	20	40	60	80	100
Temperature (K)	273	293	323	353	373
Length of air Column(cm) Proportional to volume	20.0	21.5	22.9	24.4	25.9	27.3
Use this to show a relationship!

Boyles’ Law

Pressure (kPa)	100	111	125	143	167	250
volume of air column(cm3)	50.0	45.0	40.0	35.0	30.0	20.0
Use this to show a relationship!
Use this column to get values to put into a graph

Combined Gas Law

Pressure (kPa)	100	125	250	100	125	250
volume of air column(cm3)	50.0	40.0	20.0	45.5	47.0	24.9
Temperature (K)	300	300	300	273	353	373
Use this column to get values to put into a graph

TASK:

Use the KINETIC THEORY to explain how:

pressure would vary with volume;

volume would vary with temperature;

pressure would vary with temperature.

Then try the experiments.

For each one:

Draw a diagram of the apparatus.

Draw a table and graph of the results

Record the law as a conclusion.

Don’t get caught out! LEARN THESE AND SAVE YOURSELF SOME GRIEF!

What causes pressure?

Pressure is caused by the force of particles on the walls of the container, ie F/A

KINETIC THEORY

All particles are moving.

Pressure is caused when the particles collide with the container walls

The hotter the particles the faster they move.

The faster they move the more often and more violent the collisions with the walls, greater impulse therefore greater force.

If the volume is less they will collide more often as there is a shorter distance between the container walls.

A few common explanations

For a FIXED MASS OF GAS at CONSTANT TEMPERATURE pressure is inversley proportional to the volume P1V1 = k

For a FIXED MASS OF GAS at CONSTANT PRESSURE temperature (Kelvin) is proportional to the volume V1 / T(K)1 = k

For a FIXED MASS OF GAS at CONSTANT VOLUME temperature (Kelvin) is proportional to the pressure P1 / T(K)1 = k

Content Statements Associated with the Gas laws

Describe how the kinetic model accounts for the pressure of a gas.

State that the pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume.

State that the pressure of a fixed mass of gas at constant volume is directly proportional to its temperature measured in Kelvin (K).

State that the volume of a fixed mass of gas at constant pressure is directly proportional to its temperature measured in Kelvin (K).

Carry out calculations to convert temperatures in oC to K and vice versa.

Carry out calculations involving pressure, volume and temperature of a fixed mass of gas using the general gas equation.

Explain what is meant by absolute zero of temperature.

Explain the pressure-volume, pressure-temperature and volume-temperature laws qualitatively in terms of the kinetic model.

GAS LAWS/ TUTORIAL 1

A bicycle pump has a barrel filled with air at atmospheric pressure, 1 x 105 Pa. As he inflates the tyre, this is compressed by the cyclist to a volume of 33.8 cm3 at a pressure of 6.5 x 105 Pa. If we assume that the air in the pump keeps at a constant temperature, what is the volume of the pump before the handle is pressed down?

A bottle containing air at atmospheric pressure and a temperature of 293 K, falls into a bonfire where its temperature rises to 879 K. What is the new pressure of the air in the bottle?

The fuel-air mixture in a cylinder is at a pressure of 8 x 105 Pa and a temperature of 293 K before the spark ignites it. What is the new pressure inside the cylinder if the burning mixture reaches a temperature of 1172 K before the piston has a chance to move?

A girl fills a 20 ml syringe with air at 1 x 105 Pa and puts her finger over the end as she presses the plunger down. What volume does she squash the air down to when she causes a pressure of 5.25 x 105 Pa inside the syringe?

[HELP] The three gas laws, p1V1 = p2V2 for a fixed amount of gas at constant temperature, and for a fixed mass of gas at constant volume, can be combined to give a general gas law The equation can be used to solve both types of gas behaviour problems by "cancelling out" the unwanted variable.

e.g. A fixed mass of gas at a constant volume has its temperature increased from 350 K to 525 K. If its original pressure is 0.8 x 105 Pa, what pressure does it finally reach? The new pressure is 1.2 105Pa

Make up your own problems using the general gas law and then solve them.

The pressure of air in a car tyre is 2.5 x 105 Pa at a temperature of 27 ºC. After a motorway journey the pressure has risen to 3.0 x 105 Pa. Assuming the volume of the tyre has not changed:

Calculate the temperature of the air in the tyre after the journey.

Explain the change in pressure in terms of the motion of the air particles in the tyre.

Change the following Celsius temperatures into Kelvin temperatures,

-273 ºC

-150 ºC

500 ºC,

Change the following Kelvin temperatures into Celsius temperatures,

0 K

272 K

500 K.

A fixed mass of air occupies a volume of 0.2 m3 at a temperature of 0 ºC. At what temperature will its volume be 0.4 m3 if its pressure remains unchanged?

A weather balloon contains 100 m3 of helium when atmospheric pressure is 90 kPa. If atmospheric pressure changes to 100 kPa, calculate the new volume of helium at the same temperature.

GAS LAWS/ TUTORIAL 2

A fixed mass of gas is enclosed in an insulated container whose volume is suddenly reduced:
Explain what happens to

The number of collisions per second that the molecules make with the container walls.

The average spacing between the molecules.

The kinetic energy of the molecules.

When air is pumped out of a metal can it collapses as indicated in the diagram.
Explain this effect in terms of air pressure.

A boy used the following apparatus to test a hypothesis that “the pressure of a gas is directly proportional to its temperature”.
He obtained the following results:

Temperature (ºC)	0	20	40	60	80	100
Pressure (kN m–2)	90	96	103	110	117	123

Comment on the volume of the enclosed air during the experiment.

Draw a graph of the results and show how a relationship between pressure and temperature of gas may be deduced.

Rewrite the hypothesis in a more correct form.

How could the errors be reduced in this experiment?

A graduated glass tube containing air trapped below a mercury thread is immersed in a beaker of water. When the temperature of the water is 27 ºC, the volume of the air trapped is 0.12 cm3.

Draw a graph which shows how the volume in cm3 of this trapped air changes with temperature in Kelvin.

What volume does the air occupy when its temperature is 77 ºC?

Describe how the glass tube could be used to find the temperature in degrees Celsius of a freezing mixture of ice and salt.

Explain why the accuracy of this “thermometer” would be affected by changes in atmospheric pressure.

A quantity of gas is trapped in a cylinder by a close fitting piston. The cylinder also contains a heating coil.
The piston is pushed down from position A to B and held there.

State what change occurs in the pressure of the trapped gas.

Use the particle model of the gas to explain this change.
The heating coil is switched on and the piston is held in position B.

State what happens to the molecules of the gas during the time the heating coil is on.

Use the particle model of the gas to explain this pressure change.

The petrol-air mixture in the cylinder of a car engine is ignited when the piston is in the position shown.

Explain in terms of the motion of the molecules of the gas in the cylinder why the piston moves downwards.

Use the kinetic theory of a gas to explain why the pressure of a fixed mass of gas increases as the temperature of the gas increases.

Two students wish to investigate the relationship between the pressure and temperature of a fixed mass of gas.
Describe a suitable experiment which they could carry out.
Your description should include:

a labelled sketch of the apparatus

a statement of any measurements taken

a clear indication of how these measurements could be used to show the relationship between pressure and temperature

a statement of the relationship between pressure and temperature including any conditions which apply.

A 1 kg sample of air is contained in a gas tight cylinder as shown in the diagram below. The cylinder has a moveable piston.
The sample of air is at a temperature of 0 ºC and under a pressure of 101 kPa.

The density of air at 0 ºC and a pressure of 100 kPa is 1.28 kg m-3.
Calculate the volume of air in the cylinder.

The air in the cylinder is now heated to a temperature of 70 ºC. The pressure of the air is kept constant at 101 kPa.

Calculate the new volume of the air in the cylinder.

What is the density of the air in the cylinder when the temperature of the air is 70 ºC and pressure of the air is 101 kPa?

The diagram below, taken from a physics textbook, shows the effect of increasing the force on a compression spring.
This type of spring is used in the design of a safety device for a gas cylinder.

The pressure of the gas in the cylinder is 5.0 x 105 Pa at a temperature of 20 ºC. The area of the piston is 2.5 x 10-4 m2.

What is the size of the force exerted by the gas on the piston?

Explain how the device operates, if the gas pressure in the cylinder exceeds a safety limit.

The safety limit is set at a pressure of 9.0 x 105 Pa.
At what temperature would this limit be reached by the gas described in part (a)? Assume that any increase in volume of the gas in the cylinder can be neglected.

The adjuster is screwed inwards.
What would be the effect on the value of the pressure safety limit? Justify your answer.

A pupil uses the apparatus below to investigate properties of a sample of gas.
The volume of the sample of gas can be changed by moving the piston.
The temperature of the sample of gas can be increased by using the heater.
At the start, the pressure of the gas is 400 kPa and its volume is 1000 cm3.
During the investigation, the pressure and volume of the gas change as indicated by sections AB and BC on the graph below.
During section AB, the temperature of the gas is constant at 300 K.

Calculate the volume of the gas when its pressure is 250 kPa during stage AB

State what happens to the pressure, volume and temperature of the gas over the section of the graph which starts at B and finishes at C.

What is the temperature of the gas, in Kelvin, corresponding to point C on the graph?

A cylinder of compressed oxygen gas is in a laboratory.

The oxygen inside the cylinder is at a pressure of 2.82 x 106 Pa and a temperature of 19.0 ºC.

Calculate the pressure of the oxygen inside the cylinder when its temperature is 5.0 ºC.

What effect, if any, does this decrease in temperature have on the density of the oxygen in the cylinder?
Justify your answer.

The volume of oxygen inside the cylinder is 0.030 m3.
The density of the oxygen inside the cylinder is 37.6 kg m-3.
Calculate the mass of oxygen in the cylinder.

The valve on the cylinder is opened slightly so that oxygen is gradually released.
The temperature of the oxygen inside the cylinder remains constant.
Explain, in terms of particles, why the pressure of the gas inside the cylinder decreases.

After a period of time, the pressure of the oxygen inside the cylinder reaches a constant value of 1.01 x 105 Pa. The valve remains open.
Explain why the pressure does not decrease below this value.

2008 Exam Paper

2007 Exam Paper

GAS LAWS/ TUTORIAL ANSWERS

Tutorial 1

1.	The original volume is 219.7cm3

2.	The new pressure is 3x105Pa (3 atmos.)

3.	The new pressure is 3.2x106Pa

4.	The new volume is 3.81ml

5.	a)	The new temperature is 360K = 87oC

b)	Each air molecule has more kinetic energy. If the molecules have more kinetic energy then the average speed of the molecules increase. This leads to an increase in pressure as the molecules more collisions with the tyre walls.

6.	a)	0 K

b)	123 K

c)	773 K

d)	-273 oC

e)	-1 oC

f)	227 oC

7.	T = 546 K = 273oC

8.	The new volume of helium would be 90m3

Tutorial 2

1.	a)	The smaller volume requires less travel time.

b)	The smaller volume leaves less available space.

c)	The molecules rebound with a greater velocity than they struck it with.

2.	There are therefore fewer particles to collide with the walls of the container.

3.	a)	The volume remains constant.

b)	The temperature is converted into Kelvin.

c)	The pressure of a fixed mass of gas is directly proportional to its temperature in Kelvin.

d)	The long tube to the Bourdon gauge. Aluminium foil can be added. (+ any other reasonable answers).

V(m3) T(k)

4.	a)

b)	The air occupies a volume of 0.14cm3.

c)	The glass tube can be calibrated. You could draw a calibration graph of V against T(K) for that tube. The temperature of the mixture could be found from the graph.

d)	If the pressure in the room changes then the volume would not vary proportionally.

5.	a)	As the piston is moved down the pressure of the trapped gas increases.

b)	The air molecules have much less space in which to move and so collide with the walls of the container more often.

c)	The molecules have a greater average kinetic energy. So the particles move faster.

d)	If the move faster they will make more collisions with the contianer walls.

e)	The petrol and air mixture ignites releasing energy. This increases the pressure inside the cylinder. As the volume of the cylinder can be altered the piston is forced downwards.

P1 = 400kPa, V1 = 1000cm3 P2 = 250kPa V2 = ? P1V1 = P2V2 V2 = P1V1/P2 V2 = 400x1000/250 V2 = 1600cm3
The pressure increases. The volume remains constant. The temperature increases.
The starting pressure is that indicated by point B on the graph and the final pressure is that indicated by point C. Over this period the volume is constant. T1 = 300K, P1 = 200kPa, T2 = ?, P2 = 500kPa P1/T1 = P2/T2 T2 = P2(T1/P1) T2 = 500(300/200) T2 = 750K