Uses of Magnetism (OCR GCSE Physics A (Gateway))

Higher Tier Only

The diagram below shows the structure of a transformer.

The alternating current in the secondary coil is greater than in the primary coil.

Explain why.

Higher Tier Only

The secondary coil produces an output of 12 V.

Calculate the number of turns in the secondary coil.

Show your working.

Higher Tier Only

A transformer is used to increase voltage from 25 000 V up to 400 000V before transmission through the National Grid. Therefore, the voltage increases by 16 times.

i) Explain how this increase in voltage would affect the current, assuming that the power remains constant.

ii) The formula to work out power is:    

power = current² × resistance

Explain, using a calculation, why this increase in voltage is important to power loss in transmission cables.

Higher Tier Only

A teacher demonstrates the motor effect using the equipment shown in the diagram.

A piece of copper wire, Q, is placed on two bare wires connected to a cell and switch.

When the switch is closed, wire Q moves.

i) Use Fleming’s left-hand rule to predict the direction in which wire Q moves.

ii) Describe how you used Fleming’s left-hand rule to determine the direction in which wire Q moves.

iii) Using ideas about magnetic fields, explain why wire Q moves.

Higher Tier Only

Describe what happens to the motion of wire Q when the magnetic field of the magnet is reversed.

Higher Tier Only

A current of 6.0 A passes through wire Q.

The magnetic flux density of the field is 0.64 T. The length of wire Q in the magnetic field is 0.40 m.

Calculate the force acting on wire Q.

Give your answer to 2 significant figures.

Use the Equation Sheet.

Force = ...................................................... N

Higher Tier Only

A student investigates a simple electric motor as shown in the diagram.

Explain why the coil turns when a current flows.

Higher Tier Only

(i) State the direction in which the coil turns. Put a ring around the correct option.

clockwise‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ anticlockwise

[1]

(ii) State the name of the rule you used to work this out.

[1]

Higher Tier Only

A current of 2.5 A flows in the coil, which is 0.25 m long and 0.15 m wide.

The force on one side of the coil is 0.50 N.

Calculate the magnetic flux density of the magnet.

Use the Equation Sheet.

Magnetic flux density = .................................... T

Suggest two ways in which the size of the force on the coil could be increased.

Fig. 1.1 shows a wire passing between two poles of a permanent magnet.

Fig. 1.1

The length of the wire within the magnetic field is 30 cm. The magnetic flux density of the field between the poles is 0.10 T.

The wire has a resistance of 0.2 Ω and dissipates 5.0 J of energy every second. 

The current travels out of the plane of the page.

Calculate the force exerted on the wire and state its direction.

Give your answer to 2 significant figures.

Use the Equation Sheet.

Force = .................................... N

Direction: ........................................

Fig. 1.2 shows a diagram of a loudspeaker.

Fig. 1.2

Explain why an alternating current in the coil causes the speaker cone to oscillate.