P6.7. Magnetism and Electromagnetism

Where are the magnetic forces of a magnet strongest?

At its poles.

What happens when two like magnetic poles are brought together?

They repel.

What happens when two unlike magnetic poles are brought together?

They attract.

Why are attraction and repulsion between magnetic poles non-contact forces?

The magnets exert forces on each other without physically touching.

What is a permanent magnet?

A magnet that produces its own magnetic field.

What is an induced magnet?

A material that becomes magnetic when placed in a magnetic field.

What type of force does induced magnetism always cause?

An attractive force.

What happens to an induced magnet when it is removed from the magnetic field?

It loses most or all of its magnetism quickly.

What is the difference between a permanent magnet and an induced magnet?

A permanent magnet produces its own magnetic field, whereas an induced magnet only becomes magnetic when placed in a magnetic field.

What is a magnetic field?

The region around a magnet where a force acts on another magnet or magnetic material.

Which materials are magnetic?

Iron, steel, cobalt and nickel.

What type of force acts between a magnet and a magnetic material?

Always an attractive force.

How does magnetic field strength change with distance from a magnet?

The field becomes weaker as distance increases.

Where is the magnetic field strongest around a bar magnet?

At the poles.

What does the direction of a magnetic field at a point represent?

The direction of the force that would act on a north pole placed at that point.

What is the direction of magnetic field lines outside a magnet?

From the north-seeking pole to the south-seeking pole.

What does a magnetic compass contain?

A small bar magnet.

Why does a compass needle point in a particular direction?

It aligns with the Earth's magnetic field.

How can you plot the magnetic field pattern of a magnet using a compass?

Place a compass at different positions around the magnet and record the direction in which the compass needle points.

What should a magnetic field diagram show?

The pattern, direction and relative strength of the magnetic field.

How is magnetic field strength represented on a field diagram?

Lines closer together represent a stronger field.

How can the magnetic field of a bar magnet be represented?

With field lines going from the north-seeking pole to the south-seeking pole outside the magnet, with closer lines near the poles.

What does the Earth's magnetic field provide evidence for?

That the Earth's core must be magnetic.

Why does a compass provide evidence that Earth's core is magnetic?

The compass needle aligns with Earth's magnetic field.

What happens around a wire when an electric current flows through it?

A magnetic field is produced.

What affects the strength of the magnetic field around a current-carrying wire?

The current through the wire and the distance from the wire.

What happens to the magnetic field strength around a wire when current increases?

It increases.

What happens to the magnetic field strength around a wire as distance from the wire increases?

It decreases.

What happens when a wire is shaped into a solenoid?

The magnetic field produced by the current becomes stronger.

What is a solenoid?

A coil of wire carrying a current.

What is the magnetic field inside a solenoid like?

Strong and uniform.

What is the magnetic field around a solenoid similar to?

The magnetic field around a bar magnet.

How can the magnetic effect of a solenoid be increased?

Increase the current, use more turns of wire and add an iron core.

What happens when an iron core is placed inside a solenoid?

The magnetic field becomes stronger.

What is an electromagnet?

A solenoid with an iron core.

How can the magnetic effect of a current be demonstrated?

Pass a current through a wire and observe the magnetic field it produces, for example using a compass.

What should you be able to draw for a current-carrying straight wire?

The magnetic field pattern, including its direction.

What should you be able to draw for a current-carrying solenoid?

The magnetic field pattern, including its direction.

What is the motor effect?

The force produced when a current-carrying conductor is placed in a magnetic field.

What happens between a current-carrying conductor and the magnet producing the magnetic field?

They exert forces on each other.

What does Fleming's left-hand rule show?

The relative directions of force, current and magnetic field.

In Fleming's left-hand rule, what does the first finger represent?

The magnetic field.

In Fleming's left-hand rule, what does the second finger represent?

The conventional current.

In Fleming's left-hand rule, what does the thumb represent?

The force or motion.

What factors affect the size of the force on a current-carrying conductor in a magnetic field?

The magnetic flux density, the current and the length of conductor in the magnetic field.

What is the equation for the force on a conductor at right angles to a magnetic field?

F = BIl.

What does F represent in F = BIl?

Force, in newtons (N).

What does B represent in F = BIl?

Magnetic flux density, in tesla (T).

What does I represent in F = BIl?

Current, in amperes (A).

What does l represent in F = BIl?

Length of conductor in the magnetic field, in metres (m).

What happens to the force on a conductor if the current increases?

The force increases.

What happens to the force on a conductor if the magnetic flux density increases?

The force increases.

What happens to the force on a conductor if the length of conductor in the magnetic field increases?

The force increases.

What happens when a current-carrying coil is placed in a magnetic field?

The coil tends to rotate.

What is the basic principle of an electric motor?

A current-carrying coil in a magnetic field experiences forces that cause it to rotate.

How does the motor effect make a coil rotate?

Forces act on opposite sides of the current-carrying coil in opposite directions, producing a turning effect.

What is an electric motor based on?

The motor effect.