Revision Library

revisionlibrary.co.uk

KS3 · Physics

K12 Electricity and Magnetism

AQA KS3 AQA KS3 Science (non-statutory) · Calculator allowed · about 75 minutes

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Four standard circuit symbols are described below (no diagram needed, use the descriptions):
Symbol W: a long straight line and a short straight line, parallel to each other with a gap between them.
Symbol X: a plain rectangle (box).
Symbol Y: a circle with the letter A inside it.
Symbol Z: a circle with a cross (X shape) inside it.

(a)Which symbol (W, X, Y or Z) represents a cell?(1)

(b)Which symbol represents a resistor?(1)

(c)Which symbol represents an ammeter?(1)

Circuit quantities have precise scientific meanings.

(a)State what is meant by the term "electric current".(1)

(b)State what is meant by the term "potential difference (voltage)".(1)

For each statement about circuits, state whether it is true or false.

(a)"In a series circuit, the current is the same at every point in the circuit."(1)

(b)"In a parallel circuit, the potential difference is the same across each parallel branch."(1)

(c)"Adding more resistors in series decreases the total resistance of a circuit."(1)

(d)"Adding more resistors in parallel decreases the total resistance of a circuit."(1)

Use the equation Q = I x t (charge = current x time).

(a)A current of 3 A flows through a lamp for 40 s. Calculate the charge that flows.(2)

(b)A different circuit transfers 500 C of charge when a current of 2 A flows. Calculate how long the current flows for.(2)

Use the equation V = I x R (potential difference = current x resistance).

(a)A current of 0.5 A flows through a resistor of resistance 12 ohm. Calculate the potential difference across the resistor.(2)

(b)State the unit of resistance.(1)

A series circuit contains a 12 V battery, an ammeter, and two resistors R1 = 4 ohm and R2 = 8 ohm connected one after the other.
Use R_total = R1 + R2 and V = I x R_total.

(a)Calculate the total resistance of the circuit.(1)

(b)Calculate the current shown on the ammeter.(2)

(c)State the current that flows through R1.(1)

A 12 V supply is connected to two resistors, R1 = 6 ohm and R2 = 3 ohm, arranged in parallel with each other.
Use I = V / R for each branch.

(a)State the potential difference across R2.(1)

(b)Calculate the current through R1.(2)

(c)Calculate the current through R2.(2)

(d)Calculate the total current supplied by the battery.(1)

A balloon is rubbed on a woollen jumper. The balloon becomes charged and can then stick to a wall.

(a)Explain, in terms of electrons, why the balloon becomes charged when it is rubbed on the jumper.(2)

(b)Explain why the charged balloon sticks to the wall.(2)

Static electricity has both everyday uses and hazards.

(a)Give one everyday use of static electricity.(1)

(b)A conducting strap connects a fuel tanker to the ground before fuel is transferred. Explain why this reduces the risk of fire.(2)

(c)Suggest one other everyday situation where static electricity could be a hazard, and explain how the risk is reduced.(2)

Some materials are magnetic and some are not.

(a)Which of these materials is magnetic: copper, iron, aluminium, plastic?(1)

copper
iron
aluminium
plastic

(b)Name two other elements (besides iron) that are magnetic.(2)

(c)State whether a magnet attracts or repels a piece of unmagnetised iron.(1)

(Required Practical) A student uses a plotting compass to investigate the magnetic field pattern around a bar magnet.

(a)Describe the method the student should use to plot the magnetic field pattern with a plotting compass.(3)

(b)State the direction of magnetic field lines outside a bar magnet.(1)

(c)The student notices the field lines are closest together near the poles of the magnet. What does this tell you about the magnetic field strength there?(2)

An electromagnet is made by wrapping insulated wire in a coil around an iron core.

(a)State two ways of increasing the strength of an electromagnet.(2)

(b)A student increases the current through an electromagnet from 1 A to 3 A. Predict what happens to the number of paperclips the electromagnet can pick up.(1)

(c)Explain, in terms of magnetic fields, why adding an iron core increases the strength of an electromagnet.(2)

(Required Practical) A student investigates how the length of a nichrome wire affects its resistance. The wire is connected in a circuit with a power supply, an ammeter and a voltmeter, and the length in the circuit is changed using a crocodile clip. Results:
Length (cm): 10, 20, 30, 40, 50
Resistance (ohm): 1.0, 2.0, 3.0, 4.0, 5.0

(a)Name one piece of apparatus needed for this investigation (other than the wire, ammeter and voltmeter), and state its purpose.(2)

(b)Explain why the current should only be switched on for short periods during this investigation.(2)

(c)Describe the pattern shown by the results.(1)

(d)Using the pattern in the results, calculate the resistance of a 35 cm length of this wire.(2)

(e)The student repeats the investigation with a thicker wire of the same material and the same length. State and explain the effect on the resistance.(2)

Use the equation P = V x I (power = potential difference x current).

(a)A device is connected to a 230 V supply and draws a current of 4 A. Calculate the power of the device.(2)

(b)State the unit of power.(1)

Use the equation E = P x t (energy transferred = power x time), where P is in watts and t is in seconds.

(a)A 2 kW electric heater is switched on for 30 minutes. Calculate the energy transferred, in joules.(3)

(b)State the energy transferred by the heater in kilowatt-hours (kWh).(1)

A circuit has a 12 V battery connected to a resistor R1 = 2 ohm in series with a parallel combination of R2 = 6 ohm and R3 = 3 ohm.
Use 1 / R_parallel = 1 / R2 + 1 / R3 and R_total = R1 + R_parallel and V = I x R.

(a)Calculate the combined resistance of R2 and R3 in parallel.(2)

(b)Calculate the total resistance of the circuit.(1)

(c)Calculate the total current supplied by the battery.(2)

(d)Calculate the current that flows through R2.(2)

A series circuit contains a fixed resistor of 5 ohm and a variable resistor R, connected to a 15 V supply.
Use V = I x R_total.

(a)The ammeter reads 1.5 A. Calculate the total resistance of the circuit.(2)

(b)Calculate the value of the variable resistor R.(1)

(c)The variable resistor is adjusted so its resistance doubles. Explain what happens to the current in the circuit.(2)

(d)Calculate the new current when the variable resistor's value has doubled.(2)

Explain how a simple electromagnet works, and describe one everyday application of an electromagnet. In your answer, evaluate why an electromagnet is more useful than a permanent magnet in that application.

(6)

An electrical appliance is rated at 230 V, 1150 W. Use I = P / V.

(a)Calculate the normal operating current of the appliance.(2)

(b)Standard fuses come in 3 A, 5 A and 13 A ratings. State and explain which fuse should be used for this appliance.(2)

A family runs a 3 kW electric heater for 5 hours. Electricity costs 28p per kWh.

(a)Calculate the energy used by the heater, in kWh.(2)

(b)Calculate the cost of running the heater, in pounds sterling.(2)

(Required Practical - evaluation) Referring back to the wire resistance investigation in Question 13, the student noticed the wire got noticeably warm during testing, and each length was only tested once.

(a)Explain how the wire heating up could have affected the accuracy of the results.(2)

(b)Suggest one improvement to the method that would reduce this source of error, and explain why it would help.(2)

(c)The student tested each length only once. Suggest one improvement to make the results more reliable, and explain why.(2)

Mark scheme · K12 Electricity and Magnetism

Question 1

(a) B1 W
(a) Answer: W
(b) B1 X
(b) Answer: X
(c) B1 Y
(c) Answer: Y

Question 2

(a) B1 the rate of flow of (electric) charge, oe
(a) Answer: The rate of flow of electric charge.
(b) B1 the energy transferred per unit (coulomb) of charge that flows between two points, oe
(b) Answer: The energy transferred per coulomb of charge that flows between two points in a circuit.

Question 3

(a) B1 True
(a) Answer: True
(b) B1 True
(b) Answer: True
(c) B1 False
(c) Answer: False
(d) B1 True
(d) Answer: True

Question 4

(a) M1 Q = 3 x 40
(a) A1 120 C cao
(a) Answer: 120 C
(b) M1 t = Q / I = 500 / 2
(b) A1 250 s cao
(b) Answer: 250 s

Question 5

(a) M1 V = 0.5 x 12
(a) A1 6 V cao
(a) Answer: 6 V
(b) B1 ohm (or symbol Omega)
(b) Answer: Ohm (symbol: Omega)

Question 6

(a) B1 12 ohm cao
(a) Answer: 12 ohm
(b) M1 I = 12 / 12
(b) A1 1 A cao
(b) Answer: 1 A
(c) B1 1 A ft from (b), because current is the same everywhere in a series circuit
(c) Answer: 1 A

Question 7

(a) B1 12 V, because parallel branches share the supply pd
(a) Answer: 12 V
(b) M1 I1 = 12 / 6
(b) A1 2 A cao
(b) Answer: 2 A
(c) M1 I2 = 12 / 3
(c) A1 4 A cao
(c) Answer: 4 A
(d) B1 6 A ft, from I1 + I2 = 2 + 4
(d) Answer: 6 A

Question 8

(a) B1 electrons are transferred from the jumper to the balloon (by friction)
(a) B1 the balloon gains extra electrons so becomes negatively charged
(a) Answer: Electrons transfer from the jumper to the balloon by friction, so the balloon gains negative charge.
(b) B1 the balloon's charge induces an opposite charge on the surface of the wall
(b) B1 opposite charges attract, holding the balloon in place
(b) Answer: The balloon's charge induces an opposite charge on the wall's surface, and opposite charges attract.

Question 9

(a) B1 e.g. photocopiers, electrostatic paint spraying, electrostatic smoke/dust precipitators (any one, oe)
(a) Answer: Photocopiers use static charge to attract toner powder onto paper.
(b) B1 the strap allows any static charge that builds up (from friction of fuel flow) to flow away to earth
(b) B1 this prevents a spark from forming that could ignite flammable fuel vapour
(b) Answer: Earthing lets built-up static charge flow safely to the ground instead of discharging as a spark that could ignite fuel vapour.
(c) B1 a plausible hazard situation, e.g. flour mills/dust in the air, oxygen use in hospitals, walking on synthetic carpet near sensitive electronics
(c) B1 a suitable matching risk-reduction method, e.g. earthing equipment, anti-static wrist straps, humid air/anti-static mats
(c) Answer: e.g. Dust in a flour mill can ignite from a static spark; earthing equipment and metal ducting lets charge flow away safely, preventing sparks.

Question 10

(a) B1 iron
(a) Answer: Iron
(b) B1 nickel
(b) B1 cobalt
(b) Answer: Nickel and cobalt
(c) B1 attracts
(c) Answer: Attracts

Question 11

(a) B1 place the plotting compass at a chosen point close to the magnet and mark the direction it points with a dot or arrow
(a) B1 move the compass so its tail sits on the mark just made, and mark the new direction it points
(a) B1 repeat this until a full line reaches the other pole; repeat the whole process from several different starting points around the magnet
(a) Answer: Mark successive compass directions point-to-point from several starting positions to trace complete field lines around the magnet.
(b) B1 from the north pole to the south pole
(b) Answer: From north pole to south pole.
(c) B1 field lines closer together represent a stronger magnetic field
(c) B1 so the magnetic field is strongest near the poles
(c) Answer: The magnetic field is strongest near the poles, because field line spacing shows field strength (closer lines = stronger field).

Question 12

(a) B1 increase the current flowing through the coil
(a) B1 increase the number of turns of wire on the coil (or add/keep an iron core)
(a) Answer: Increase the current, and/or increase the number of turns of wire on the coil.
(b) B1 the number of paperclips picked up increases
(b) Answer: The number of paperclips picked up increases.
(c) B1 the iron core becomes magnetised (an induced magnet) while current flows
(c) B1 this concentrates and adds to the magnetic field produced by the coil, making it stronger
(c) Answer: The iron core becomes an induced magnet and its field adds to the coil's field, concentrating and strengthening the overall magnetic field.

Question 13

(a) B1 apparatus named, e.g. metre rule/ruler, low-voltage power supply, or crocodile clips
(a) B1 matching correct purpose, e.g. ruler to measure the length of wire accurately
(a) Answer: A metre rule, used to measure the length of wire being tested accurately.
(b) B1 a large current flowing for a long time causes the wire to heat up
(b) B1 heating increases the resistance of the wire, which would make the results inaccurate
(b) Answer: Keeping the current on briefly stops the wire heating up, since heating would increase its resistance and make results inaccurate.
(c) B1 resistance is directly proportional to length (as length doubles, resistance doubles), oe
(c) Answer: Resistance is directly proportional to the length of wire.
(d) M1 resistance per cm = 0.1 ohm/cm (from the data), so R = 0.1 x 35
(d) A1 3.5 ohm cao
(d) Answer: 3.5 ohm
(e) B1 resistance decreases
(e) B1 a thicker wire has a larger cross-sectional area, giving charge carriers more space/pathways to flow, so resistance is lower
(e) Answer: Resistance decreases, because a thicker wire has a larger cross-sectional area, offering less opposition to the flow of charge.

Question 14

(a) M1 P = 230 x 4
(a) A1 920 W cao
(a) Answer: 920 W
(b) B1 watt (W)
(b) Answer: Watt (W)

Question 15

(a) M1 convert: 2 kW = 2000 W and 30 minutes = 1800 s
(a) M1 E = 2000 x 1800
(a) A1 3 600 000 J (3.6 x 10⁶ J) cao
(a) Answer: 3,600,000 J (3.6 x 10⁶ J)
(b) B1 1 kWh, from 2 kW x 0.5 h
(b) Answer: 1 kWh

Question 16

(a) M1 1 / R_parallel = 1/6 + 1/3 = 1/2
(a) A1 R_parallel = 2 ohm cao
(a) Answer: 2 ohm
(b) B1 4 ohm ft, from R1 + R_parallel = 2 + 2
(b) Answer: 4 ohm
(c) M1 I = 12 / 4
(c) A1 3 A cao
(c) Answer: 3 A
(d) M1 voltage across parallel section = I x R_parallel = 3 x 2 = 6 V
(d) A1 I2 = 6 / 6 = 1 A cao
(d) Answer: 1 A

Question 17

(a) M1 R_total = 15 / 1.5
(a) A1 10 ohm cao
(a) Answer: 10 ohm
(b) B1 5 ohm ft, from R_total minus the fixed resistor: 10 - 5
(b) Answer: 5 ohm
(c) B1 total resistance of the circuit increases
(c) B1 as the supply voltage is unchanged, the current must decrease (V = I x R)
(c) Answer: The current decreases, because total resistance increases while the supply voltage stays the same.
(d) M1 new R_total = 5 + 10 = 15 ohm, so I = 15 / 15
(d) A1 1 A cao
(d) Answer: 1 A

Question 18

Level 1 (1-2): Simple statements are made about electromagnets or an application, with limited scientific detail and little or no linkage between ideas.
Level 2 (3-4): The basic operation of an electromagnet is explained with some correct detail. A relevant application is described, but the evaluation of why an electromagnet is preferable to a permanent magnet is incomplete or only partly correct.
Level 3 (5-6): A clear and logically structured explanation of how the electromagnet works is given, a relevant application is described accurately, and a full evaluation is provided of why an electromagnet (rather than a permanent magnet) is used, with sound reasoning throughout.
Indicative content:
- Current flowing through a coil of insulated wire produces a magnetic field around the coil.
- Wrapping the wire in a coil (solenoid shape) makes the individual field lines from each turn add together, strengthening the overall field.
- Placing an iron core inside the coil concentrates the field further, because the iron becomes magnetised (an induced magnet) only while current flows.
- The magnetic field can be switched on and off simply by switching the current on and off.
- The strength of the field can be varied by changing the size of the current, or the number of turns on the coil.
- Reversing the direction of the current reverses the polarity of the electromagnet.
- Application example: an electromagnetic crane in a scrapyard/recycling centre lifts and sorts scrap iron and steel.
- The magnet can be switched off to release the load exactly where needed, which a permanent magnet cannot do.
- Application example: an electric bell, where an electromagnet attracts an iron striker to hit a bell, then releases it as the circuit breaks, repeating automatically.
- A permanent magnet's strength and polarity cannot be controlled or turned off, so it is unsuitable where controllable attraction/release is needed.

Question 19

(a) M1 I = 1150 / 230
(a) A1 5 A cao
(a) Answer: 5 A
(b) B1 13 A
(b) B1 the fuse rating must be above the normal operating current (5 A) or it will blow during ordinary use; 3 A is too low and a 5 A fuse would blow right at the normal operating current, so 13 A is the safe/correct choice
(b) Answer: 13 A fuse, because it must be rated above the 5 A operating current without being so close that ordinary use trips it.

Question 20

(a) M1 E = 3 x 5
(a) A1 15 kWh cao
(a) Answer: 15 kWh
(b) M1 cost = 15 x 28
(b) A1 GBP 4.20 cao
(b) Answer: GBP 4.20

Question 21

(a) B1 heating a wire increases its resistance
(a) B1 so the measured resistance values would be higher than the true resistance at that length, making the results less accurate
(a) Answer: Heating increases resistance, so the measured values would be higher than the true resistance, reducing accuracy.
(b) B1 e.g. only close the switch briefly to take each reading, or use a lower current/voltage
(b) B1 this reduces heating of the wire, so the measured resistance is closer to its true value at room temperature
(b) Answer: Only switch on briefly to take each reading; this limits heating so the resistance measured is closer to the true value.
(c) B1 repeat the reading at each length (at least three times) and calculate a mean
(c) B1 this reduces the effect of random error or anomalous readings, making the results more reliable
(c) Answer: Repeat each length reading several times and take a mean, which reduces the effect of random error and anomalies.

Electricity and Magnetism - Worksheets, Questions and Revision