Magnetism and Electromagnetism

By the end of this topic you should know:

Magnetic materials, electromagnets and the Earth create magnetic fields which can be described by drawing field lines to show the strength and direction. 

The stronger the magnet, and the smaller the distance from it, the greater the force a magnetic object in the field experiences.

Two 'like' magnetic poles repel and two 'unlike' magnetic poles attract.

Field lines flow from the north-seeking pole to the south-seeking pole.

An electromagnet uses the principle that a current through a wire causes a magnetic field. Its strength depends on the current, the core and the number of coils in the solenoid.

The magnetic force of an electromagnet decreases with distance.

By the end of this topic you should be able to:

Use the idea of field lines to show how the direction or strength of the field around a magnet varies.

Explain observations about navigation using Earth's magnetic field.

Predict the pattern of field lines and the force around two magnets placed near each other.

Predict how an object made of a magnetic material will behave if placed in or rolled through a magnetic field.

Use a diagram to explain how an electromagnet can be made and how to change its strength.

Explain the choice of electromagnets or permanent magnets for a device in terms of their properties.

Suggest how bells, circuit breakers and loudspeakers work, from diagrams.

By the end of this topic you should understand these key words:

Magnetic force: Non-contact force from a magnet on a magnetic material.

Permanent magnet: An object that is magnetic all of the time.

Magnetic poles: The ends of a magnetic field, called north-seeking (N) and south-seeking poles (S).

Electromagnet: A non-permanent magnet turned on and off by controlling the current through it.

Solenoid: Wire wound into a tight coil, part of an electromagnet.

Core: Soft iron metal which the solenoid is wrapped around.