Magnetic Effects of Electric Current

Lesson

Part 1 — the magnetic field of a bar magnet, and the surprising discovery that an electric current makes a magnetic field too.

In this lesson you will

Draw field-line patterns around a bar magnet and state the properties of magnetic field lines
Apply the right-hand thumb rule to find the field direction around a straight wire and a circular loop
Describe the field inside a solenoid and how it is used to make an electromagnet

Concept

Magnets, compasses and magnetic fields

A compass needle is a small bar magnet; its north-seeking end is its north pole. The region around a magnet in which its force can be detected is its magnetic field. A field has both strength and direction.

Table: like poles repel and unlike poles attract; a freely suspended magnet points north and south, as a compass needle does; the field direction at a point is where a compass north pole points
Fact	Example
Like poles repel, unlike poles attract	Two N poles push apart
A freely suspended magnet points north–south	Compass needle
The field direction at a point is the way a compass N pole points there	Compass placed near a bar magnet

Diagram

Field lines around a bar magnet

Field lines are traced here from a model of the magnet’s two poles. They leave the N pole and enter the S pole, and they never cross.

Iron filings or a small compass trace field lines: they leave the N pole, curve round and enter the S pole.

Cookies