Electromagnetism & The Motor Effect Flashcards

All 12 cards in this deck

What are the steps to show that a current in a wire creates a magnetic field?
e.g. using a power pack, a wire, a card and iron filings

1. Put the wire through a hole in the card and connect the wire to a power pack.
2. Sprinkle iron filings on the card and switch on, so there is a current in the wire.
3. Tap the card — the filings move into circles around the wire.

What shape are the magnetic field lines around a long straight current-carrying wire?

Circles around the wire.
An arrow on a field line (e.g. clockwise) shows the direction of the field.

True or false? Reversing the direction of the current in a wire reverses the direction of its magnetic field.

True.
The circular field lines stay the same shape but the arrows point the other way round.

What is the relationship between the magnetic field strength around a wire and the size of the current?

Directly proportional.
As the current increases, the field strength increases in even steps.

True or false? The magnetic field around a current-carrying wire is strongest close to the wire.

True.
The field gets weaker further from the wire, so the field lines are closer together near it.

What is a solenoid?

A coil of wire that acts as an electromagnet when there is a current in it.

What is the magnetic field like inside a solenoid, and why?

Strong and almost uniform along the centre, because the fields from the individual coils add together.

Why is the magnetic field outside a solenoid weaker than inside it?

The fields from the individual coils cancel each other outside the solenoid.

Give two ways to make the magnetic field of a solenoid stronger.

Increase the current; increase the number of turns on the coil (or add an iron core).

True or false? An electromagnet such as a solenoid stays magnetised after the current is switched off.

False.
It is a temporary magnet — its magnetism can be switched off by switching off the current.

How do you use the right-hand thumb rule to find the direction of the magnetic field around a current-carrying wire?

Grip the wire with your right hand so your thumb points along the current. Your curled fingers show which way the field circles the wire.

What shape is the magnetic field outside a solenoid?

The same shape as the field around a bar magnet, with a north pole at one end and a south pole at the other.