Practise drawing fields around wires and solenoids, predicting their strength and direction and explaining how current-operated relays use electromagnetism.
Fig. 9.2 represents a current in a wire. The current is into the plane of the paper.
Draw the pattern of the magnetic field produced around the wire. Show clearly the direction of the magnetic field.
Fig. 9.2
The direction of the current in the wire is reversed. The magnitude of the current is unchanged.
State the effect that reversing the current has on the magnetic field produced.
The electric starter motor in a car is switched on and off using a relay.
The relay consists of a plastic case and two flexible springy strips, X and Y, which are made of soft iron. These iron strips act as the switch when a circuit is connected between the terminals W and Z.
Fig. 7.1 shows \(\mathrm{X
Fig. 7.2 shows the equipment from Fig. 7.1 inside a magnetising coil. The magnetising coil is in series with the 12 V car battery and switch S , which is open.
Switch S is now closed.
Explain what happens to the springy iron strips X and Y .
Fig. 10.1 shows a wire that carries a current into the page. The circles on Fig. 10.1 show the pattern of the magnetic field around the wire.
Fig. 10.1
On Fig. 10.1, draw an arrow on each circle to show the direction of the magnetic field. [1]
State why the spacing of the circles increases as the distance from the wire increases.