IGCSE Physics 0625 — Topic 4: Electricity & Magnetism

Question 1

Two bar magnets are placed end-to-end with a north pole facing a south pole. What is the shape of the magnetic field lines in the gap between them?

AThe field lines curve away from each other, forming loops that go outward BThe field lines run as nearly straight, parallel lines from the north pole to the south pole CThere is a neutral point where no field lines exist DThe field lines form closed loops around each pole independently

Question 2

A plotting compass is placed at a point between two magnets with their north poles facing each other. The compass needle does not settle in any direction. What is this point called?

AA magnetic pole BA neutral point CA magnetic equator DA field line crossing

Question 3

A student brings a magnet near a steel paper clip. The paper clip is attracted. She then brings the magnetised paper clip near another unmagnetised paper clip. What happens to the second paper clip?

AIt is repelled because both clips have the same poles BIt is attracted because the first clip induces magnetism in the second CNothing happens because a paper clip cannot become a magnet DIt is attracted only if the second clip is made of iron, not steel

Question 4

Which statement correctly describes the difference between magnetically hard and magnetically soft materials?

AHard materials are easy to magnetise and easy to demagnetise BSoft materials retain their magnetism permanently CHard materials are difficult to magnetise but retain their magnetism well DSoft materials cannot be used in electromagnets

Question 5

An electromagnet is made by wrapping wire around an iron core. Which change would decrease the strength of the electromagnet?

AReplacing the iron core with a steel core BIncreasing the current in the coil CAdding more turns of wire to the coil DReducing the current in the coil

Question 6

An electromagnet is used in a scrapyard crane to lift old cars. Why is an electromagnet used rather than a permanent magnet?

AA permanent magnet would be too heavy for the crane BAn electromagnet can be switched off to release the car CPermanent magnets do not attract steel DAn electromagnet only attracts non-magnetic materials

Question 7

Which of the following materials is NOT magnetic?

AIron BCobalt CCopper DNickel

Question 8

A student has two metal rods that look identical. One is a magnet and one is unmagnetised iron. She is only allowed to use the two rods. How can she determine which rod is the magnet?

ATouch the end of rod X to the end of rod Y — if they attract, rod X is the magnet BTouch the end of rod X to the middle of rod Y — the magnet will always attract at the middle of the other rod, but the iron rod will not attract the middle of the magnet CSuspend rod X from a string — the magnet will always point north-south DHold them side by side — the magnet will be heavier

Question 9

A current of 0.5 A flows through a lamp for 4 minutes. What is the total charge that flows through the lamp?

A2 C B8 C C120 C D200 C

Question 10

A voltmeter is used to measure the potential difference across a component. How should the voltmeter be connected?

AIn series with the component BIn parallel with the component CIn series with the battery DBetween the switch and the battery only

Question 11

A battery has an EMF of 9 V. When it is connected to a circuit, the potential difference across its terminals is 8.4 V. What does the “lost” 0.6 V represent?

AEnergy wasted as heat inside the battery due to its internal resistance BEnergy stored in the wires of the circuit CThe charge that leaks out of the battery DA measurement error in the voltmeter

Question 12

A resistor has a resistance of 20 Ω and a current of 1.5 A flows through it. What is the potential difference across the resistor?

A0.075 V B13.3 V C21.5 V D30 V

Question 13

An I-V graph shows a curve that starts at the origin and bends so that the current increases more and more slowly as the voltage increases. Which component does this describe?

AA fixed resistor at constant temperature BA filament lamp CA diode DA thermistor being cooled

Question 14

A diode is connected in a circuit with a battery and a lamp. The lamp does not light. What is the most likely reason?

AThe diode is forward biased and has zero resistance BThe diode is reverse biased and blocks the current CThe diode has converted all the electrical energy into light DThe diode increases the resistance when forward biased

Question 15

A 230 V kettle has a resistance of 26.5 Ω. What is the power of the kettle? Use P = V²/R.

A8.7 W B2000 W C6095 W D52 900 W

Question 16

A 12 V battery is connected to a motor that draws a current of 3 A. The motor runs for 5 minutes. How much electrical energy is transferred?

A180 J B2160 J C10 800 J D36 000 J

Question 17

A 3 kW heater is used for 2.5 hours. Electricity costs $0.15 per kWh. What is the cost of using the heater?

A$0.45 B$1.13 C$5.00 D$7.50

Question 18

How many joules of energy are in 1 kilowatt-hour (kWh)?

A1000 J B60 000 J C3 600 000 J D36 000 000 J

Question 19

A current of 2 A passes through a wire with a potential difference of 6 V. The power dissipated in the wire can also be calculated using P = I²R. What is the resistance of the wire?

A0.33 Ω B3 Ω C8 Ω D12 Ω

Question 20

A charge of 50 C passes through a resistor. The potential difference across the resistor is 12 V. How much energy is transferred in the resistor?

A4.2 J B62 J C600 J D6000 J

Question 21

Three resistors of 4 Ω, 6 Ω and 10 Ω are connected in series with a 12 V battery. What is the voltage across the 6 Ω resistor?

A2.4 V B3.6 V C6.0 V D12 V

Question 22

A 6 Ω resistor and a 3 Ω resistor are connected in parallel. A current of 3 A flows from the battery. What is the current through the 6 Ω resistor?

A0.5 A B1 A C1.5 A D2 A

Question 23

Two resistors of 12 Ω each are connected in parallel. What is their combined resistance?

A3 Ω B6 Ω C12 Ω D24 Ω

Question 24

In a circuit, a 4 Ω resistor is connected in series with a parallel combination of two 10 Ω resistors. The circuit is connected to a 9 V battery. What is the total current drawn from the battery?

A0.375 A B0.9 A C1 A D2.25 A

Question 25

In a series circuit, increasing the number of identical lamps connected to the same battery causes each lamp to become dimmer. Why?

AThe total resistance increases, so the current decreases and each lamp gets a smaller share of the voltage BThe battery supplies less energy when more lamps are added CEach lamp receives more current but at a lower voltage DThe total voltage of the battery decreases when more lamps are connected

Question 26

A potential divider consists of a 15 Ω resistor and a 5 Ω resistor connected in series to a 10 V supply. What is the voltage across the 5 Ω resistor?

A2.0 V B2.5 V C5.0 V D7.5 V

Question 27

A potential divider circuit has a thermistor in series with a fixed resistor, connected to a 6 V battery. The output voltage is measured across the fixed resistor. As the temperature increases, what happens to the output voltage?

AIt increases, because the thermistor resistance decreases so a larger share of voltage falls across the fixed resistor BIt decreases, because the thermistor resistance decreases CIt stays the same, because the battery voltage is constant DIt drops to zero because thermistors become superconductors at high temperature

Question 28

A light-dependent resistor (LDR) is connected in series with a 10 kΩ fixed resistor to a 5 V supply. The output voltage is taken across the LDR. In bright light the LDR has a resistance of 1 kΩ. In darkness it has a resistance of 100 kΩ. What is the approximate output voltage across the LDR in bright light?

A0.45 V B2.5 V C4.55 V D5.0 V

Question 29

A 230 V appliance is rated at 920 W. Which fuse should be used?

A1 A B3 A C5 A D13 A

Question 30

A metal-cased appliance develops a fault so that the live wire touches the metal case. The appliance has an earth wire connected. What happens?

AThe metal case remains live and dangerous to touch BA large current flows through the earth wire to ground, blowing the fuse and disconnecting the supply CThe neutral wire absorbs the excess current and the appliance continues to work normally DThe earth wire increases the resistance and reduces the current to a safe level

Question 31

What is the advantage of a circuit breaker over a fuse?

AA circuit breaker is cheaper to buy BA circuit breaker reacts faster and can be reset without replacement CA circuit breaker allows higher currents to flow safely DA circuit breaker does not need to be connected to the live wire

Question 32

A plastic-cased power tool has only two wires in its cable: live and neutral. It has no earth wire. Why is this safe?

AThe plastic case is an insulator, so even if a live wire comes loose, current cannot flow through the user via the case BThe neutral wire acts as a substitute earth wire CPower tools operate at low voltage so no earth wire is needed DThe fuse provides enough protection without an earth wire regardless of the case material

Question 33

A straight wire is moved rapidly downward through a horizontal magnetic field. What happens?

AThe wire becomes permanently magnetised BAn EMF is induced across the ends of the wire CA current flows only if the wire is made of a magnetic material DThe magnetic field is destroyed by the wire’s movement

Question 34

A coil of wire is connected to a sensitive galvanometer. A magnet is held stationary inside the coil. What does the galvanometer read?

AA large constant deflection BA small fluctuating deflection CZero — no EMF is induced because there is no relative motion DA deflection that gradually increases over time

Question 35

In a simple a.c. generator, the coil rotates in a magnetic field. What is the purpose of the slip rings?

ATo reverse the current direction every half turn so the output is d.c. BTo maintain continuous electrical contact with the rotating coil while allowing it to spin freely CTo increase the frequency of the alternating current produced DTo strengthen the magnetic field around the coil

Question 36

A transformer has a primary coil with 200 turns connected to a 240 V supply. The secondary coil produces an output of 12 V. How many turns are on the secondary coil?

A10 B24 C100 D4000

Question 37

An ideal step-up transformer increases the voltage from 25 V to 500 V. The current in the primary coil is 10 A. What is the current in the secondary coil?

A0.5 A B2 A C200 A D5000 A

Question 38

A current-carrying wire is placed between the poles of a horseshoe magnet. The wire experiences a force that pushes it upward. If both the current direction and the magnetic field direction are reversed, what happens to the force on the wire?

AThe force reverses direction and pushes the wire downward BThe force remains upward because both reversals cancel out CThe force becomes zero because the field and current cancel DThe force doubles in magnitude

Question 39

The magnetic field inside a solenoid carrying a current can be made stronger by inserting a core. Which material is the best choice for the core to make the strongest electromagnet that can also be switched off?

ACopper BSteel CSoft iron DAluminium

Question 40

Electricity is generated at a power station at 25 kV. It is stepped up to 400 kV for transmission through power lines. The power transmitted is 200 MW. What is the current in the transmission cables?

A0.5 A B500 A C8000 A D50 000 A

Paper 2 — Multiple Choice

Section A — Magnetism

Section B — Electrical Quantities

Section C — Electric Circuits

Section D — Electrical Safety

Section E — Electromagnetic Effects