1. 1
   A cyclist's bicycle has a small dynamo that presses against the spinning wheel; inside the dynamo, a magnet rotates near a coil of wire, lighting the bicycle's front lamp as the cyclist pedals.

   (a)

   What is the name of the effect that causes a voltage to be produced in the coil as the magnet rotates near it?

   [1 mark]

   • Aelectromagnetic induction
   • Btotal internal reflection
   • Cthermal conduction
   • Dradioactive decay

   (b)

   The cyclist pedals faster, making the magnet in the dynamo rotate more quickly. What effect does this have on the voltage induced in the coil?

   [1 mark]

   • AThe induced voltage decreases
   • BThe induced voltage increases
   • CThe induced voltage stays exactly the same
   • DNo voltage is induced at any speed

   (c)

   State two factors, other than the speed of rotation, that affect the size of the voltage induced in the dynamo's coil, and explain how the coil could be redesigned to increase the induced voltage without pedalling faster.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A large power station generator produces electricity by rotating a coil of wire within a strong magnetic field at a steady rate.

   (a)

   What type of electrical output does this generator produce?

   [1 mark]

   • Ano current is produced by rotation alone
   • Bdirect current (d.c.) only
   • Calternating current (a.c.)
   • Da constant, unchanging voltage

   (b)

   What happens to the size of the voltage induced in the generator's coil if it is made to rotate faster, with the magnetic field strength unchanged?

   [1 mark]

   • AThe induced voltage is unaffected by rotation speed
   • BThe induced voltage decreases
   • CThe induced voltage becomes negative
   • DThe induced voltage increases

   (c)

   Explain how the direction of the induced current in the generator's coil changes as the coil completes one full rotation, and why this produces an alternating rather than direct current.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An electricity company needs to transmit power from a distant power station to a city many kilometres away using overhead cables, and uses transformers at each end of the transmission line.

   (a)

   Describe the basic structure of a transformer and explain how it is able to change the size of an alternating voltage between its primary and secondary sides.

   [3 marks]

   (b)

   A step-up transformer at the power station has 200 turns on its primary coil and 8000 turns on its secondary coil, and is connected to a primary voltage of 11,000 V. Calculate the secondary (transmission) voltage, and explain why the electricity company chooses to transmit power at such a high voltage rather than at the original 11,000 V.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineering student is designing a hand-cranked emergency generator for use during power outages, consisting of a coil of wire that can be made to rotate rapidly within the field of a strong permanent magnet by turning a hand crank connected to a system of gears.

   (a)

   Explain the physics of how turning the crank produces an alternating voltage in the coil, and describe three separate ways the student could increase the size of the voltage produced by the generator for a given cranking speed.

   [6 marks]

   (b)

   The student connects the generator's output to a small step-up transformer with 50 turns on the primary coil and 500 turns on the secondary coil, intending to power a device that requires a higher voltage than the generator alone provides. If the generator produces an alternating voltage of 6 V and delivers a current of 2 A into the primary coil of the transformer, calculate the secondary voltage and the secondary current assuming the transformer is 100% efficient, and explain why real transformers can never be perfectly 100% efficient in practice.

   [6 marks]

   Total for question 4: 12 marks

End of questions