Solenoids & Electromagnets

What is a solenoid?

A coil of wire that produces a magnetic field when current flows through it.

Why does coiling a wire increase its magnetic effect?

The magnetic fields from the individual turns combine, producing a stronger field.

What is the magnetic field like inside a long solenoid?

Strong and approximately uniform.

What is the shape of the magnetic field around a solenoid?

Similar to that of a bar magnet.

Where are the north and south poles of a solenoid?

At its opposite ends.

How can the magnetic field direction of a solenoid be determined?

Use the right-hand grip rule, curling fingers with conventional current so the thumb points towards the north pole.

What happens to the poles of a solenoid when the current is reversed?

The north and south poles swap ends.

What is an electromagnet?

A solenoid with an iron core.

Why is an iron core placed inside a solenoid?

It increases the magnetic field strength.

Why is soft iron useful as an electromagnet's core?

It is easily magnetised and loses most of its magnetism when the current stops.

How can an electromagnet be made stronger?

Increase the current, increase the number of turns or add an iron core.

How does increasing current affect an electromagnet?

It produces a stronger magnetic field.

How does increasing the number of turns affect an electromagnet?

It produces a stronger magnetic field.

How can an electromagnet be switched off?

Switch off the current through the coil.

What is an advantage of an electromagnet over a permanent magnet?

Its magnetic field can be switched on and off.

What is another advantage of an electromagnet?

Its magnetic field strength can be varied by changing the current.

Why are electromagnets useful in scrap-metal cranes?

They can attract magnetic materials and release them when switched off.

How can the magnetic field of a solenoid be plotted?

Use a plotting compass at different positions to identify field direction.

How do field lines inside a solenoid differ from those outside?

Inside, they are approximately straight, parallel and closely spaced; outside, they curve around.

What happens if a solenoid's current is reversed while its iron core remains in place?

The magnetic field direction reverses, but the core still strengthens the field.

Why is an electromagnet useful in devices requiring controlled movement?

Its magnetic force can be controlled electrically.