1. 1
   A furniture restorer holds a permanent bar magnet stud finder near a wooden door to detect hidden steel nails and screws before drilling into the wood.

   (a)

   Why does the stud finder's magnet attract the steel nails and screws hidden inside the door?

   [1 mark]

   • AThe nails are magnetic materials that become induced magnets in the stud finder's field, and are attracted
   • BThe nails repel the magnet because they have the same magnetic pole
   • CWood conducts a magnetic field directly into the nails
   • DThe nails are themselves permanent magnets that attract the stud finder

   (b)

   Which of these materials would NOT be attracted by the stud finder's magnet?

   [1 mark]

   • AIron
   • BCopper
   • CSteel
   • DNickel

   (c)

   Explain the difference between the magnetism of the stud finder's permanent magnet and the induced magnetism of a steel nail near it.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineering student builds a simple electromagnet for a school project by wrapping a coil of insulated wire (a solenoid) around an iron nail and connecting the ends of the wire to a battery.

   (a)

   What is created around the coil of wire when a current flows through it?

   [1 mark]

   • AAn electric field only
   • BNo field is created unless the coil touches a magnet
   • CA magnetic field
   • DA gravitational field

   (b)

   Which change would increase the strength of the electromagnet's magnetic field?

   [1 mark]

   • ARemoving the iron nail from inside the coil
   • BDecreasing the current in the coil
   • CUsing a longer, straight wire instead of a coil
   • DIncreasing the number of turns of wire in the coil

   (c)

   Explain why shaping the wire as a solenoid, rather than leaving it as a straight wire, increases the strength of the magnetic field around it.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician tests a straight copper rod of length 0.25 m, carrying a current of 6 A, held at right angles to a magnetic field of flux density 0.4 T produced by a pair of magnadur magnets.

   (a)

   State Fleming's left-hand rule and explain what each of the three directions it shows represents for the rod in this test.

   [3 marks]

   (b)

   Calculate the force on the rod due to the motor effect.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hand-cranked emergency radio contains a small generator: turning a hand crank rotates a magnet inside a fixed coil of wire, inducing a potential difference that charges the radio's internal battery. The radio can also be charged by a small solar panel.

   (a)

   Explain the generator effect and how turning the hand crank in the emergency radio generates a potential difference across the coil. Explain what would happen to the size of the induced potential difference if the crank were turned more quickly, and why this happens.

   [6 marks]

   (b)

   Explain, using the idea that an induced current generates a magnetic field that opposes the change producing it, why turning the hand crank becomes harder as the internal battery gets closer to fully charged and draws more current.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   An electronics hobbyist uses a small transformer to convert the potential difference from a 230 V wall socket down to 9.2 V to power a model train set. The transformer's primary coil has 2500 turns.

   (a)

   What is this transformer, which reduces the potential difference from a higher to a lower value?

   [1 mark]

   • AA step-down transformer
   • BA step-up transformer
   • CA rectifier
   • DA solenoid

   (b)

   Which equation correctly relates the potential differences and turns of a transformer's coils?

   [1 mark]

   • AVp x np = Vs x ns
   • BVp/Vs = np/ns
   • CVp + Vs = np + ns
   • DVp - Vs = np - ns

   (c)

   Calculate the number of turns on the secondary coil of the transformer.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A recycling plant sorts mixed metal waste using an overhead electromagnet, built from a coil of insulated wire wound around a soft iron core connected to a variable-voltage power supply, positioned above a conveyor belt of crushed cans.

   (a)

   Which of these materials would the electromagnet be able to lift from the conveyor belt?

   [1 mark]

   • AAluminium cans
   • BPlastic bottles
   • CSteel cans
   • DGlass bottles

   (b)

   Which change to the electromagnet would increase its lifting strength?

   [1 mark]

   • AReducing the number of turns of wire
   • BRemoving the iron core
   • CUsing a thicker conveyor belt
   • DIncreasing the current supplied to the coil

   (c)

   Explain why switching off the current to the electromagnet allows the operator to drop the collected steel cans into a separate container, whereas a permanent magnet could not be used in the same way.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A 100% efficient step-up transformer at a small hydroelectric plant increases the potential difference from the generator, 400 V, to 2000 V before the electricity is sent along a local transmission cable. The primary coil carries a current of 50 A.

   (a)

   Calculate the current in the secondary coil of the transformer, assuming it is 100% efficient.

   [3 marks]

   (b)

   Explain, using your answer to part (a), one advantage of transmitting electrical power at a higher potential difference and lower current along a cable, in terms of energy losses, and calculate the power supplied by the generator to the primary coil.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   An engineer compares two devices that both use a coil of wire and a magnetic field: an electric motor, which uses a current-carrying coil in a magnetic field to produce rotation, and a hand-turned generator, which rotates a coil within a magnetic field to induce a current.

   (a)

   Explain how the motor effect causes a current-carrying coil placed in a magnetic field to rotate continuously in an electric motor, and explain the role of a split-ring commutator in this process.

   [6 marks]

   (b)

   Explain how the generator effect in the hand-turned generator is essentially the reverse process of the motor effect used in the electric motor, and explain why the generator produces an alternating current (ac) rather than a direct current (dc) as the coil rotates.

   [6 marks]

   Total for question 8: 12 marks

End of questions