Magnetic effect of a current Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

What is a current-carrying solenoid?

A coil of wire whose turns produce a combined magnetic field.

What is the magnetic field pattern outside a solenoid?

Like a bar magnet’s field, the field lines curve from the north pole to the south pole.

What is the magnetic field like inside a long solenoid?

It is approximately uniform, with nearly parallel field lines directed from south to north.

How can the right-hand rule identify a solenoid’s north pole?

Curl the fingers in the direction of conventional current around the turns; the thumb points towards the north pole.

What happens to a solenoid’s magnetic field when its current is reversed?

The field reverses direction and the north and south poles swap.

How can a plotting compass be used to map a current-produced magnetic field?

Close the circuit and place the compass at successive positions, marking the direction of its north-seeking end. Join the marks to form field lines and add arrows for their direction.

How is a straight wire positioned to map its magnetic field with a compass?

Pass the wire through a horizontal card and connect it to a circuit.

How should a solenoid be positioned for magnetic field mapping with a compass?

Arrange the coil so that the compass can reach points around it.

What can iron filings show about a magnetic field that they cannot show about its direction?

They show the shape of the field pattern, but not its direction. A compass is needed to establish direction.

What happens to the direction of a current-produced magnetic field when the current is reversed?

The field direction reverses.

Why should the current be switched off between magnetic field measurements?

To limit heating.

What does an electromagnetic relay allow a small control current to do?

Operate a switch in a separate circuit carrying a larger current.

What happens to the iron core and armature when a relay coil is energised?

The coil’s magnetic field magnetises the iron core, which attracts the armature.

How does the armature operate the controlled circuit in a relay?

It moves the switch contacts, opening or closing the circuit.

What returns a relay’s armature when the coil is switched off?

A spring returns it once the magnetic attraction is removed.

What energy conversion does a moving-coil loudspeaker perform?

It converts an electrical signal into sound.

How are the coil, cone and magnet arranged in a moving-coil loudspeaker?

A coil attached to a lightweight cone lies in the magnetic field of a permanent magnet.

What produces a force on the coil of a moving-coil loudspeaker?

The coil current’s magnetic field interacts with the permanent magnet’s field.

How does a changing audio current affect the force on a loudspeaker coil?

The force changes in size and direction.

How do vibrations of a loudspeaker’s coil produce sound waves?

The attached cone vibrates with the coil, making the surrounding air vibrate.