IGCSE Physics 0625 — Topic 4: Electricity & Magnetism

Question 1

A bar magnet is suspended freely by a thread. The north pole of a second bar magnet is brought close to the south pole of the suspended magnet. What happens to the suspended magnet?

AIt is repelled away from the second magnet BIt is attracted towards the second magnet CIt spins continuously DNothing happens

Question 2

Which diagram correctly shows the magnetic field lines around a bar magnet?

ALines run from south pole to north pole outside the magnet, with arrows pointing towards the north pole BLines run from north pole to south pole outside the magnet, with arrows pointing away from the north pole CLines run parallel to each other from north pole to south pole DLines form concentric circles around the magnet

Question 3

A piece of soft iron is placed near the north pole of a permanent magnet. Which statement about the soft iron is correct?

AThe end nearest the magnet becomes a north pole and it is repelled BThe end nearest the magnet becomes a south pole and it is attracted CBoth ends become north poles DThe soft iron is not affected because it is not a magnet

Question 4

Steel is described as a magnetically hard material. What does this mean?

AIt is difficult to magnetise but retains its magnetism well BIt is easy to magnetise but loses its magnetism quickly CIt cannot be magnetised at all DIt is physically harder than iron

Question 5

Which change would increase the strength of an electromagnet?

AReplacing the iron core with a wooden core BReducing the number of turns on the coil CIncreasing the current through the coil DUsing a longer, thinner core

Question 6

In a relay, an electromagnet is used to close a switch in a separate high-current circuit. Why is a relay useful?

AIt allows a small current to control a circuit carrying a large current BIt converts a.c. to d.c. CIt increases the voltage in a circuit DIt reduces the total resistance in the circuit

Question 7

A compass is placed at a point between two bar magnets arranged with their north poles facing each other. The compass needle does not point towards either magnet. What can be concluded about that point?

AThere is no magnetic field at that point — it is a neutral point BThe magnetic field is very strong at that point CThe compass is broken DBoth magnets have lost their magnetism

Question 8

A student has two iron bars that look identical. One is a magnet and the other is unmagnetised. Without using any other equipment, how can the student determine which bar is the magnet?

ATouch the end of one bar to the middle of the other — if there is attraction, the one being touched in the middle is the magnet BTouch the end of one bar to the middle of the other — if there is attraction, the one touching with its end is the magnet CBring the ends together — if they attract, the bar on the left is the magnet DDrop both bars — the magnet will fall more slowly

Question 9

A current of 0.50 A flows through a lamp for 4.0 minutes. What is the total charge that flows through the lamp?

A2.0 C B8.0 C C120 C D480 C

Question 10

Electric current is the flow of charge. What is the unit of current and how is it measured in a circuit?

AVolt, measured with a voltmeter in parallel BAmpere, measured with an ammeter in series CAmpere, measured with an ammeter in parallel DCoulomb, measured with an ammeter in series

Question 11

What is the difference between electromotive force (e.m.f.) and potential difference (p.d.)?

AE.m.f. is the energy supplied per unit charge by the source; p.d. is the energy converted per unit charge by a component BE.m.f. is always larger than p.d. because it includes extra resistance CP.d. is measured in volts but e.m.f. is measured in joules DE.m.f. only applies to a.c. circuits; p.d. only applies to d.c. circuits

Question 12

A resistor has a potential difference of 12 V across it and a current of 0.40 A flowing through it. What is the resistance of the resistor?

A4.8 Ω B12.4 Ω C30 Ω D0.033 Ω

Question 13

Which I–V graph shows the characteristic of an ohmic conductor (a wire at constant temperature)?

AA straight line through the origin BA curve that gets steeper as V increases CA curve that flattens off as V increases DA horizontal line above the V-axis

Question 14

A filament lamp is connected to a variable power supply. As the voltage is increased, the current increases but not proportionally. Why does the resistance of the filament increase?

AThe filament gets longer as it heats up BThe metal atoms vibrate more at higher temperatures, impeding the flow of electrons CThe number of free electrons decreases at higher temperatures DThe voltage across the lamp decreases as the current rises

Question 15

An electric heater operates at 230 V and draws a current of 8.0 A. What is the power of the heater?

A28.75 W B238 W C1840 W D14 720 W

Question 16

A 6.0 Ω resistor carries a current of 3.0 A. What is the power dissipated in the resistor?

A2.0 W B18 W C54 W D108 W

Question 17

A 12 V battery drives a current of 2.5 A through a motor for 200 s. How much electrical energy is transferred to the motor?

A30 J B2400 J C6000 J D48 000 J

Question 18

A 2.0 kW electric oven is used for 3.0 hours. The cost of electricity is $0.15 per kWh. What is the cost of using the oven?

A$0.30 B$0.90 C$6.00 D$9.00

Question 19

A charge of 600 C flows through a component that has a potential difference of 9.0 V across it. What is the energy transferred?

A66.7 J B609 J C5400 J D54 000 J

Question 20

The I–V graph for a component passes through the origin. At V = 4.0 V the current is 0.80 A, and at V = 8.0 V the current is 0.80 A. What is the component?

AAn ohmic resistor BA filament lamp CA diode DA thermistor

Question 21

Three lamps are connected in series to a battery. The current through the first lamp is 0.30 A. What is the current through the third lamp?

A0.10 A B0.30 A C0.90 A DIt depends on the resistance of each lamp

Question 22

Two identical resistors are connected in parallel across a 6.0 V battery. What is the potential difference across each resistor?

A3.0 V B6.0 V C12.0 V DIt depends on the resistance of the resistors

Question 23

A 4.0 Ω resistor, a 6.0 Ω resistor and a 10 Ω resistor are connected in series. What is the total resistance?

A1.9 Ω B6.7 Ω C20 Ω D240 Ω

Question 24

Two resistors of 12 Ω and 6.0 Ω are connected in parallel. What is the combined resistance?

A2.0 Ω B4.0 Ω C9.0 Ω D18 Ω

Question 25

A circuit contains a 6.0 Ω resistor in series with a parallel combination of two 12 Ω resistors. The battery e.m.f. is 12 V. What is the current from the battery?

A0.50 A B1.0 A C2.0 A D4.0 A

Question 26

In a potential divider circuit, a 10 Ω resistor is connected in series with a 30 Ω resistor across a 12 V supply. What is the potential difference across the 30 Ω resistor?

A3.0 V B4.0 V C9.0 V D12 V

Question 27

A thermistor is connected in series with a fixed resistor across a battery. A voltmeter measures the p.d. across the fixed resistor. What happens to the voltmeter reading when the temperature increases?

AIt increases, because the thermistor resistance decreases so more voltage is dropped across the fixed resistor BIt decreases, because the thermistor resistance decreases CIt stays the same, because the battery voltage is constant DIt decreases, because the thermistor resistance increases

Question 28

An LDR is connected in series with a fixed resistor and a battery. A voltmeter is connected across the LDR. What happens to the voltmeter reading when the light intensity increases?

AIt increases, because the LDR resistance increases in bright light BIt decreases, because the LDR resistance decreases in bright light and so less voltage is dropped across it CIt stays the same DIt increases, because more current flows in bright light

Question 29

An appliance operates at 230 V and has a power rating of 920 W. The available fuse ratings are 3 A, 5 A, 10 A and 13 A. Which fuse should be used?

A3 A B5 A C10 A D13 A

Question 30

An appliance with a metal case is connected to the mains supply using a three-pin plug. What is the purpose of the earth wire?

AIt carries the normal operating current back to the power station BIt provides a low-resistance path to earth if the live wire touches the metal case, causing the fuse to blow CIt reduces the voltage to a safe level DIt increases the resistance of the circuit so the current is smaller

Question 31

In a correctly wired three-pin plug, which wire is connected to the fuse?

AThe earth wire (green and yellow) BThe neutral wire (blue) CThe live wire (brown) DBoth the live and neutral wires

Question 32

Some appliances have a plastic casing and are labelled “double insulated” with a two-pin plug (no earth wire). Why is no earth wire needed?

AThe plastic casing is an insulator, so the user cannot receive a shock even if a wire comes loose inside BThe appliance uses a very low voltage so it is safe CThe fuse provides all the protection needed DDouble insulated appliances always operate on batteries

Question 33

A bar magnet is pushed into a coil of wire connected to a sensitive galvanometer. The galvanometer deflects. What is this effect called?

AThe motor effect BElectromagnetic induction CStatic electricity DThe transformer effect

Question 34

A magnet is moved in and out of a solenoid to generate an e.m.f. Which change would increase the size of the induced e.m.f.?

AMoving the magnet more slowly BUsing a solenoid with fewer turns CUsing a stronger magnet and moving it faster DUsing a thicker wire for the solenoid

Question 35

A simple a.c. generator consists of a coil rotating between the poles of a magnet. What does the output look like on an oscilloscope?

AA straight horizontal line BA sinusoidal (wave) pattern that alternates above and below the zero line CA series of positive-only humps (always above the zero line) DA stepped square wave

Question 36

A transformer has 200 turns on the primary coil and 1000 turns on the secondary coil. The primary voltage is 50 V. What is the secondary voltage?

A10 V B50 V C250 V D4000 V

Question 37

An ideal transformer has a primary voltage of 240 V and a secondary voltage of 12 V. The secondary current is 5.0 A. What is the primary current?

A0.25 A B1.0 A C5.0 A D100 A

Question 38

A wire carrying a current is placed between the poles of a horseshoe magnet. The wire experiences a force. Using Fleming’s left-hand rule, if the magnetic field points from left to right and the current flows into the page, in which direction is the force on the wire?

AUpwards BDownwards CTo the left DOut of the page

Question 39

In a simple d.c. motor, what is the function of the split-ring commutator?

ATo increase the speed of the motor BTo reverse the current direction in the coil every half turn, so the coil continues to rotate in the same direction CTo convert a.c. to d.c. DTo increase the magnetic field strength

Question 40

Electrical power is transmitted from a power station to consumers through cables of total resistance 8.0 Ω. The power station delivers 100 kW. Why is a step-up transformer used to increase the transmission voltage to 100 000 V?

AHigher voltage means higher current, which delivers more power BAt higher voltage the current is smaller (I = P/V), so the power lost as heat in the cables (P = I²R) is much less CHigher voltage reduces the resistance of the cables DHigher voltage makes the electrons move faster so they do not heat the cables

Paper 2 — Multiple Choice

Section A — Magnetism

Section B — Electrical Quantities

Section C — Electric Circuits

Section D — Electrical Safety

Section E — Electromagnetic Effects