Magnetism & Electromagnetism (Edexcel IGCSE Science (Double Award): Physics)

The diagram shows an electric motor.

This electric motor needs a direct current (d.c).

Explain what is meant by the term direct current.

(i) Explain the purpose of the brushes and the commutator in a d.c. motor.

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(ii) The motor turns clockwise when the direction of the current goes from + to – . State what happens to the motor when both the magnetic field and the current are reversed.

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Diagram 1 shows some of the apparatus used to investigate the force on a current-carrying wire, XY, in a magnetic field. 

Diagram 2 shows the poles of the magnet viewed from above.

Draw the uniform magnetic field between the poles. 

The current-carrying wire XY is at right angles to the magnetic field. The current in the wire is 10 A. 

(i) Suggest why the wire used in this investigation must be thick. 

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(ii) Explain why the wire XY experiences a force when there is a current in the circuit. 

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(iii) State two ways in which this force can be reduced. 

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The diagram shows a piece of card and two wide bar magnets. 

(i) Add to the diagram to show the shape and direction of the magnetic field pattern between the magnets. 

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(ii) Describe how to investigate the shape and direction of the magnetic field between the magnets.

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A metal rod, X Y, is placed in a magnetic field as shown.

Wires from a cell are connected to the ends of the rod so that there is a current from X to Y. 

Describe the effect on the rod. 

The photograph shows a simple d.c. electric motor. 

When the switch is closed the coil spins. Explain why this happens. 

(i) Describe two ways to increase the speed of rotation of the coil in this motor. 

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(ii) Suggest how to make the coil spin in the opposite direction. 

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The diagram shows the magnetic field pattern around a bar magnet. 

Complete the diagram above by labelling the poles on the bar magnet.

Describe an experiment to investigate the shape of the magnetic field pattern of a bar magnet. You may draw a diagram to help your answer. 

Explain how to produce a uniform magnetic field. 

This photograph shows an electromagnetic device used to keep a door open. 

The electromagnet attracts the metal plate to hold the door open.

The electromagnet is connected to a fire alarm circuit.

When the fire alarm sounds, the door is released and it closes.

 State why the metal plate is made of iron.

Describe the changes that allow the electromagnet to release the door when the fire alarm sounds.

The diagram shows two identical metal rods placed inside a coil of wire.

When a direct current is supplied to the coil, a magnetic field forms and the metal rods move apart. Explain why the metal rods move apart.

When the current is switched off, the metal rods return to their starting places.

Suggest what material the metal rods are made from. Explain your answer.

The direct current in the coil is replaced by an alternating current.

Explain what will happen to the magnetic field.

A student uses this apparatus to investigate what happens to a current-carrying conductor in a magnetic field. 

The student connects the two parallel horizontal metal rails to the positive and negative terminals of a power supply.

The metal rod AB rests across the rails and is free to move.

Explain what happens to the metal rod AB.

This diagram shows the construction of a simple loudspeaker. 

A coil of wire is wrapped around a paper tube attached to the loudspeaker cone. When there is an alternating current in the coil, the cone moves.

Describe how the alternating current generates a sound wave. You may draw a diagram if it helps your answer.

In a radio, sound is produced by a loudspeaker. The diagram shows the construction of a loudspeaker.

Describe how a loudspeaker uses an electrical supply to produce sound waves.

The photograph shows a small electric motor.

Explain why the coil starts to spin when the switch is closed.

(i) Suggest how to make the coil spin in the opposite direction.

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(ii) Suggest how to make the coil spin more slowly.

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In a different motor, the magnets are curved and there is a piece of iron inside the coil. The iron increases the strength of the magnetic field through the coil.

Suggest how the curved magnets and the piece of iron improve the performance of the electric motor.

The coil is suspended vertically so that it is free to swing. A second, identical coil is placed beside it.

When direct currents pass, as shown, the two coils move together

When the current in the right-hand coil is reversed, the two coils move apart

Explain why the coils move in this way.

The wire is removed and the magnetic field between the poles changes.

Sketch the new magnetic field.

Explain how you could use a plotting compass to investigate the magnetic field around a bar magnet. You may draw a diagram to help your answer.