National 5 Physics

Electricity and Energy

Homework Booklet

Homework 1 – Movement Means Energy 1

  1. In each of the cases below, state the main energy change involved for the vehicle.

(a)A rollercoaster carriage rolling up a slope to a high point.(1)

(b)A skier skiing down a slope.(1)

(c)A bus driving along a level road at a constant speed.(1)

  1. (a)What is work done? Your answer should not be an equation!(2)

(b)Calculate the work done by a horse when it uses a force of 800 N to pull a sled a distance of 150 m. (3)

  1. Copy and complete the table below. You must show full calculations for each problem.

Power(W) / Work Done(J) / Time(s)
400 / 4
1000 / 0.5
30 / 10
100 / 60

(12)

Total marks: 20

Homework 2 - Movement Means Energy 2

1.A roller coaster carriage has a mass of 300 kg when it is carrying a full load.

(a)Calculate the potential energy of the carriage when it is at the top of a drop, 30 m above the ground. (3)

( (2)

(b)At the bottom of the drop it is at a height of 2 m above the ground.

Calculate its potential energy now. (3)

(1)

(c)Calculate how much kinetic energy the carriage will have at this point. (3)(1)

2.Name two quantities that affect a vehicle’s kinetic energy. (2)

3.A winch pulls a crate up to a height of 4 m in a time of 20 s. If the crate has a mass of 100 kg, find the power of the motor. (3) (3)

4.Find the kinetic energy of a car of mass 800 kg travelling at 30 m/s. (3)(2)

Total marks: 17

Homework 3 – Efficiency

  1. Find the missing values in the following table.

Efficiency (%) / Useful energy in(J) / Useful energy out(J)
(a) / 1 400 / 700
(b) / 675 / 135
(c) / 80 / 1 200
(d) / 45 / 1 500
(e) / 60 / 300
(f) / 25 / 6 000

(8)

  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. (3)
  1. A turbine converts 65 000 J of heat energy into 13 000 J of kinetic energy. What is the efficiency of the turbine? (3)
  1. A generator converts 3 156 MJ of kinetic energy into 450 MJ of electrical energy. What is the efficiency of the generator? (3)
  1. A thermal power station converts 420 MJ of chemical energy into 124 MJ of electrical energy. What is the efficiency of this power station?

(3)

Total marks: 20

Homework 4 - Current and Voltage

  1. What is an electric current?

(1)

  1. In a television set a current of 60 mA passing from the cathode to the screen.

(a) How much charge is delivered to the screen in 5 minutes?

(3)

(b) If an electron has a charge of 1.6 x 10-19C, how many electrons hit the screen in 5 minutes?

(1)

  1. Draw a table with two columns headed ‘Conductors’ and ‘Insulators’. In your tableput the following materials in the correct column:

Copper carbon paper aluminium

Hair tungsten plastic air

Which of these conductors is classed as a non-metal?

(5)

  1. Draw and name the circuit symbols for:

(a) A fuse

(b) A variable resistor

(2)

  1. A circuit is set up to measure the current flowing through a light bulb and to measurethe potential difference across it. The voltage supply is a battery of cells and thecurrent in the circuit is changed using a variable resistor. The current is measured withan ammeter and the potential difference with a voltmeter. Draw a circuit diagram ofthis circuit.

(3)

  1. What can be said about the current in:

(a) A series circuit?

(b) A parallel circuit?

(2)

  1. What can be said about the potential differences across the components in:

(a) A series circuit?

(b) A parallel circuit?

(2)

Total marks: 20

Homework 5 - Ohm’s Law

  1. What is meant by the ‘resistance’ of a component?

(1)

  1. What is the meaning of the term ‘voltage’ or ‘potential difference’?

(1)

  1. Copy and complete this table.

Voltage / V / Current / A / Resistance / Ω
(a) / 0·4 / 150
(b) / 0·05 / 40
(c) / 12 / 60
(d) / 8 / 400

(8)

  1. What is the resistance of a lamp that allows a current of 600 mA when there is a potential difference of 12 V across it?

(1)

  1. What is the current in a piece of 10 kΩ resistance wire when a voltage of 15 V is across it?

(1)

  1. What is the voltage across a 125 Ω lamp that has a current of 1·84 A in it?

(1)

  1. In an experiment, a resistor is connected to a variable d.c. power supply.

The power supply is adjusted to give a range of different currents and values of the current and corresponding voltage across the resistor are recorded

The results are shown in the table.

Current / A / Voltage / V
0·02 / 0·24
0·04 / 0·46
0·06 / 0·75
0·08 / 0·96
0·10 / 1·19
0·12 / 1·44

Draw a line graph of these results and use the gradient of the straight line to find the resistance of the resistor.

(3)

  1. The same experiment is repeated, except this time the resistor is replaced with a bulb. The results are shown in the table.

Current / A / Voltage / V
0·02 / 0·08
0·04 / 0·25
0·06 / 0·48
0·08 / 0·77
0·10 / 1·11
0·12 / 1·74

Draw a line graph of these results and explain why a straight line is not found.

(4)

Total marks: 20

Homework 6 - Resistors in Series and Parallel Homework

  1. What happens to the total resistance of a circuit as more resistors are connected in series? (1)
  1. Calculate the total resistance of these combinations of resistors.

(6)

  1. What happens to the total resistance of a circuit as more resistors are added in parallel?

(1)

  1. Calculate the total resistance of these combinations of resistors.

(6)

  1. Calculate the total resistance between X and Y in these circuits:

(3)

(3)

(3)

(4)

  1. In a physics lesson, a student is given three 1·2 kΩ resistors.

What is the lowest possible resistance that the student could achieve by combining these resistors?

(3)

Total marks: 30

Homework 7 –Resitance and Potential Dividers

  1. If V is the potential difference across a resistor and I is the current passing through it,what can be said about the ratio V/I when the current changes?

(1)

  1. Calculate the current through a 4.6 kW resistor when it is connected to a 230 V mainssupply.

(3)

  1. Calculate the resistance of a resistor if the current flowing through it is 9.2 x 10-3Awhen it is connected to a 230 V mains supply.

(3)

  1. Calculate the total resistance between X and Y for the following network of resistances:

(3)

  1. (a) Calculate the resistance between A and B for the following network of resistances:

(i) When switch S is open.

(ii) When switch S is closed.

(a)If a voltage supply were connected to A and B, what would happen to the current flowing through the 40 W resistor nearer to A when S is closed?

(b)What would happen to the voltage across this resistor when S is closed?

(6)

  1. What is a potential divider?

(1)

  1. In the potentiometer shown below what is the reading on the voltmeter when X is:

(i) at A?

(ii) at B?

(b) What range of voltage can the potentiometer provide?

(3)

  1. In the potential divider circuit shown below calculate the value of V1.

(3)

Total Marks: 20

Homework 8 - Power

  1. A car battery supplies 12 volts for a headlamp bulb which draws a current of 4.6 amps.

(a)What is the power rating of the bulb?(3)

  1. Another bulb with the same power rating is designed to operate from 230 volts mains electricity.

(b)What current flows through the mains bulb?(3)

(c)Which bulb has more electrons flowing through per second?(1)

(d)Which bulb has electrons with the greatest energy for each electron?(1)

  1. A table lamp has a power rating of 187 watts and draws a current of 1.7 amps.

(a)What voltage will the lamp operate with?(3)

(b)Is the lamp designed to run off UK mains electricity?(1)

  1. In the UK, mains electricity has a voltage of 230 volts.

(a)If an appliance has a 3 amp fuse fitted what is the maximum power the appliance can consume? (3)

(b)What is the maximum power a 13 amp fuse can supply?(3)

  1. A calculator is rated with a power of 0.6 milliwatts (mW) and operates from a 3 volt solar cell

(a)What current does the solar cell supply for the calculator to operate?(3)

(b)If the calculator is left on for 11 hours 30 minutes what energy is generated by the solar cell? (1)

(c)For what time would this amount of energy supply the car headlamp of question 1?

(1)

Total Marks: 23

Homework 9 - Lamps and LEDs

1.A small lamp runs off a 3 volt battery and draws a current of 0.6 amps.

a)Draw a labelled circuit diagram with ammeter and voltmeter to measure the current and voltage for the bulb. (3)

b)Calculate the resistance of the lamp.(3)

c)Calculate the power consumed by the bulb.(3)

d)If left on for 10 minutes, how much energy would be used?(3)

2.An LED will only work if it has 1.2 volts across it and a current of 0.024 amps flowing through.

a)Draw a circuit diagram with a 3 volt battery, LED and resistor connected in series.

(3)

b)Why is the resistor needed to operate the led?(1)

c)If the LED has 0.024 amps flowing through and the circuit is a series circuit, what is the current in the resistor? Mark this on your circuit diagram. (3)

d)If the voltage across the LED is 1.2 volts, the voltage of the battery is 3 volts and the circuit is a series circuit, what is the voltage across the resistor? Label this voltage on your circuit diagram. (3)

e)Using your voltage and current calculate the resistance of the resistor needed.

(f)Calculate the power consumed by the LED.(3)

3.A lamp has a power rating of 60 watts and is designed to run off a 12 volt power supply.

a)How many joules of energy will the bulb convert every second?(3)

b)What two forms of energy will the electrical energy be converted into?(1)

c)Calculate the current required by the bulb.(3)

d)Draw a circuit diagram showing how this current could be measured by an ammeter.

(3)

e)Calculate the resistance of the bulb.(3)

Total Marks: 38

Homework 10 - Pressure

  1. An office safe has a weight of 500 N. The area of the base is 1·25 square metres. Calculate the pressure on the floor of the office? (3)
  1. A physics teacher has a weight of 800 N. Her feet have an area of 0·025 square metres each. What pressure does she exert on the ground?

(Remember, physics teachers have two feet!) (3)

  1. A box exerts a pressure of 1200 Pa on the ground and has a base area of 2·2 m2. What force does it exert on the ground?

(3)

  1. Atmospheric pressure is 101 000 Pa.

(a)What force does the air exert on a wall of area 8·5 m2?(3)

(b)Why does this force not push over the wall?(1)

  1. Explain why the use of large tyres helps to prevent a tractor from sinking into soft ground.

(2)

  1. Explain the damage to classroom floors caused by pupils swinging on their chairs?

(2)

Total Marks: 17

Homework 11- Pressure and volume (constant temperature)

  1. 100 cm3 of air is contained in a syringe at normal atmospheric pressure of 100 000 Pa.
    Calculate the pressure in the syringe (without a change in temperature) when the volume is reduced to:

a) 50 cm3

b) 20 cm3.(6)

  1. If the piston in a cylinder containing 300 cm3 of gas at a pressure of 1 × 105 Pa is moved outwards so that the pressure of the gas falls to 8 × 104 Pa, find the new volume of the gas.

(3)

  1. A weather balloon contains 80 m3 of helium at normal atmospheric pressure of 1 × 105 Pa. What will be the volume of the balloon at an altitude where air pressure is 8 × 104 Pa?

(3)

  1. The cork in a pop-gun is fired when the pressure reaches 3 atmospheres. If the plunger is 60 cm from the cork when the air in the barrel is at atmospheric pressure, how far will the plunger have to move before the cork pops out? (3)
  1. A swimmer underwater uses a cylinder of compressed air which holds 15 litres of air at a pressure of 12 000 kPa.

(a)Calculate the volume this air would occupy at a depth where the pressure is
200 kPa.(3)

(b)If the swimmer breathes 25 litres of air each minute at this pressure, calculate how long the swimmer could remain at this depth (assume all the air from the cylinder is available). (3)

Total Marks: 21

Homework 12 - Pressure and Temperature (constant volume)

  1. Convert the following Celsius temperatures to kelvin.

a) -273 °Cb) -150 °Cc) 0 °C d) 27 °Ce) 150 °C

(5)

  1. Convert the following kelvin temperatures to Celsius.

a) 10 Kb) 23 Kc) 100 Kd) 350 Ke) 373 K

(5)

  1. A cylinder of oxygen at 27 °C has a pressure of 3 × 106 Pa. What will be the new pressure if the gas is cooled to 0 °C?

(3)

  1. An electric light bulb is designed so that the pressure of the inert gas inside it is
    100 kPa (normal air pressure) when the temperature of the bulb is 350 °C. At what pressure must the bulb be filled if this is done at 15 °C?

(3)

  1. The pressure in a car tyre is 2·5 × 105 Pa at 27 °C. After a long journey the pressure has risen to 3·0 × 105 Pa. Assuming the volume has not changed, what is the new temperature of the tyre?

(3)

  1. A compressed air tank, which at room temperature of 27 °C normally contains air at 4 atmospheres, is fitted with a safety valve which operates at 10 atmospheres.
    During a fire the safety valve was released. Estimate the average temperature of the air in the tank when this happened.

(3)

Total Marks: 22

Homework 13 - Volume and temperature (constant pressure)

  1. 100 cm3 of a fixed mass of air is at a temperature of 0 °C. At what temperature will the volume be 110 cm3, if its pressure remains constant?

(3)

  1. Air is trapped in a glass capillary tube by a bead of mercury. The volume of air is found to be 0·10 cm3 at a temperature of 27 °C. Calculate the volume of air at a temperature of 87 °C.

(3)

  1. The volume of a fixed mass of gas at constant temperature is found to be 50 cm3.
    The pressure remains constant and the temperature doubles from 20 °C to 40 °C.
    Explain why the new volume of gas is not 100 cm3.

(3)

  1. Describe an experiment to find the relationship between the volume and temperature of a fixed mass of gas at constant pressure. Your description should include:

(a)A diagram of the apparatus used

(b)A note of the results taken

(c)An appropriate method to find the relationship using the results.(4)

Total Marks: 13

Homework 14 -General gas equation

1.Find the unknown quantity from the readings shown below for a fixed mass of gas.

(a) / P1 = 2 × 105 Pa
P2 = 3 × 105 Pa / V1 = 50 cm3
V2 = ? / T1 = 20 °C
T2 = 80 °C
(b) / P1 = 1 × 105 Pa
P2 = 2.5 × 105 Pa / V1 = 75 cm3
V2 = 100 cm3 / T1 = 20 °C
T2 = ?
(c) / P1 = 2 × 105 Pa
P2 = ? / V1 = 60 cm3
V2 = 80 cm3 / T1 = 20 °C
T2 = 150 °C
d) / P1 = 1 × 105 Pa
P2 = 2.5 × 105 Pa / V1 = 75 cm3
V2 = 50 cm3 / T1 = ?
T2 = 40 °C

(12)

  1. A sealed syringe contains 100 cm3 of air at atmospheric pressure 1 × 105 Pa and a temperature of 27 °C. When the piston is depressed the volume of air is reduced to 20 cm3 and this produces a temperature rise of 4 °C. Calculate the new pressure of the gas.

(3)

  1. Calculate the effect the following changes have on the pressure of a fixed mass of gas.

(a) Its temperature (in K) doubles and volume halves.(1)

(b) Its temperature (in K) halves and volume halves.(1)

(c) Its temperature (in K) trebles and volume quarters.(1)

  1. Calculate the effect the following changes have on the volume of a fixed mass of gas.

(a) Its temperature (in K) doubles and its pressure halves.(1)

(b) Its temperature (in K) halves and its pressure halves.(1)

(c) Its temperature (in K) trebles and its pressure quarters.(1)

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

(2)

Total Marks: 23