Magnetism + Electromagnetism

Where are magnetic forces strongest on a magnet?

The poles of the magnet.

What happens when two unlike magnetic poles are brought together?

They attract each other.

What happens when two like magnetic poles are brought together?

They repel each other.

What are non-contact forces?

Forces that act over a distance without physical contact.

What is an induced magnet?

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

What happens when an induced magnet is removed from a 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. An induced magnet only becomes magnetic in a magnetic field and loses it quickly.

What is a magnetic field?

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

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

Always a force of attraction.

How does magnetic field strength change with distance?

It decreases as the distance from the magnet increases.

Where is the magnetic field strongest on a magnet?

At the poles.

What do magnetic field lines show?

The direction of the force that would act on a north pole placed in the field.

In which direction do magnetic field lines go?

From the north pole to the south pole.

What is the Earth’s magnetic field caused by?

The Earth acting like a large magnet.

What does a compass do?

It contains a small magnet that aligns with the Earth’s magnetic field.

What happens when a current flows through a wire?

A magnetic field is produced around the wire.

What factors affect the strength of the magnetic field around a wire?

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

How can the magnetic field inside a solenoid be described?

Strong and uniform.

How can the strength of a solenoid’s magnetic field be increased?

By increasing the current or adding an iron core.

What is an electromagnet?

A solenoid with an iron core.

When does a force act on a conductor in a magnetic field?

When it carries a current and is placed in a magnetic field.

What does Fleming’s left-hand rule show?

The direction of the force on a conductor in a magnetic field.

What factors affect the size of the force on a conductor?

Magnetic flux density, current, and length of conductor.

What is the equation for force on a conductor in a magnetic field?

F = B I l

What does F represent?

Force in newtons (N).

What does B represent?

Magnetic flux density in tesla (T).

What does I represent?

Current in amperes (A).

What does l represent?

Length of conductor in metres (m).

What happens to a current-carrying coil in a magnetic field?

It experiences a force that causes it to rotate.

What is this effect used for?

Electric motors.

How do loudspeakers and headphones work?

They use the motor effect to convert variations in current into sound waves.

What is the generator effect?

A potential difference is induced when a conductor moves relative to a magnetic field or when the magnetic field changes.

When is an induced current produced?

When the conductor is part of a complete circuit.

What does the induced current do?

It produces a magnetic field that opposes the change that caused it.

What devices use the generator effect?

Alternators and dynamos.

What does an alternator produce?

Alternating current (AC).

What does a dynamo produce?

Direct current (DC).

How do microphones work?

They use the generator effect to convert sound waves into electrical signals.

What is a transformer?

A device that changes the potential difference in an alternating current circuit.

What does a transformer consist of?

A primary coil and a secondary coil on an iron core.

Why is iron used in the core of a transformer?

Because it is easily magnetised.

Why is the core laminated?

To reduce energy losses from eddy currents.

What is the transformer equation?

Vp/Vs = np/ns

What is a step-up transformer?

Output voltage is greater than input voltage.

What is a step-down transformer?

Output voltage is less than input voltage.

What is the power relationship in a transformer?

VsIs = VpIp

What does this power relationship mean?

If the transformer is 100% efficient, input power equals output power.