Electromagnetic Induction & Alternating Currents (Edexcel A Level Physics): Exam Questions

Hybrid electric vehicles (HEV) use the same device both as a generator to charge the car battery and as an electric motor to support the propulsion system. A simplified diagram of the device is shown. The coil can rotate freely around the axis.

Describe how the device can be used as both a generator and an electric motor.

The circuit diagram shows a car battery connected to an electric motor for a HEV.

The battery has an electromotive force (e.m.f.) 180 V and internal resistance 0.036 Ω.

The motor has a maximum power of 88 kW.

i) Show that the current I drawn by the electric motor when operating at this power would be given by the equation

0.036I² − 180I + 88 000 = 0

(3)

ii) Solving the equation above produces an answer of I = 550 A. At maximum power, the car can accelerate from rest to sixty miles per hour in under 7 s.

The maximum charge capacity of the battery within this HEV is 6.1 amp-hour.

Deduce whether the battery could maintain this current for up to 7 s.

(2)

The Shanghai Maglev Train is the first commercially operated high-speed magnetic levitation train in the world, connecting the airport and central Shanghai.

The total distance travelled is 29.9 km and the total journey time is 440 s. The train starts from rest and reaches a speed of 97 m s^–1 in 120 s.

i) Calculate the average acceleration of the train during the first 120 s.

Average acceleration of train = ..............................(2)

ii) Calculate the average speed of the train for the period following the 120 s acceleration.

Average speed of train = .............................(3)

Electromagnetic forces enable the train to levitate above a steel rail.

Explain why magnetic levitation is an advantage for a high-speed transport system.

A linear induction motor provides the force to accelerate the train forwards. A current flows in sequence through coils of wire mounted in the track. The train is dragged along as the magnetic field progresses along the coils of wire in the track. This is similar to moving a permanent magnetic field away from a conductor.

A teacher demonstrates this effect by quickly removing one end of a bar magnet from a suspended aluminum ring.

When the magnet is removed from the ring, the ring moves in the same direction as the magnet.

Explain, using the laws of electromagnetic induction, why the ring moves in the direction of the magnet.

A simple electric motor consists of a coil that is free to rotate in a magnetic field.

A student connects the motor to an ammeter and a battery.

The graph shows how the current I in the coil varies with time t. The switch is closed at time T.

Explain why the current rises to a maximum then decreases.

Your answer should include a reference to Faraday and Lenz’s laws.