magnetism

At which part of a magnet are the magnetic forces strongest?

The poles of the magnet.

What happens when two magnets are brought close to each other?

They exert a force on each other.

What type of force is exerted if two like poles of a magnet are brought near each other?

A repulsive, non-contact force.

What type of force is exerted if two unlike poles of a magnet are brought near each other?

An attractive, non-contact force.

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

A permanent magnet produces its own magnetic field. An induced magnet becomes magnetic when placed in a magnetic field.

What type of force does induced magnetism always cause?

A force of attraction.

What happens when an induced magnet is removed from a magnetic field?

The induced magnet loses most/all of its magnetism.

What is a magnetic field?

The region surrounding a magnet where another magnet or magnetic material experiences a non-contact force.

Give four examples of magnetic materials.

Iron, Steel, Cobalt, Nickel.

What can always be said about the force between a magnet and a magnetic material?

It is always attractive.

How does the strength of a magnetic field alter as you move further away from the magnet producing it?

The magnetic field strength decreases the further you move away.

In what direction does a magnetic field point?

In the direction that a north pole would experience a force if placed in the field. From the north seeking pole to the south seeking pole of a magnet.

What does a magnetic compass contain?

A small bar magnet that points in the direction of the Earth’s magnetic field.

What is produced when current flows through a conducting wire?

A magnetic field is produced around the wire.

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

The magnitude of the current and the distance from the wire.

What is a solenoid?

A coil of wire which when current passes through creates a strong magnetic field.

Describe the magnetic field found inside a solenoid.

Strong and uniform.

What is an electromagnet?

A solenoid with an added iron core, which increases the magnetic field strength.

What is the motor effect? (Higher)

When a force is exerted between a magnetic field and a current-carrying conductor placed in that field.

What rule is used to determine the force experienced due to the motor effect? (Higher)

Fleming’s Left-Hand Rule.

When using Fleming’s left hand rule what does the forefinger represent? (Higher)

The direction of the magnetic field.

When using Fleming’s left hand rule what does the second finger represent? (Higher)

The direction of current flow in the conductor.

What factors affect the size of the force on a current-carrying wire in a magnetic field? (Higher)

The current magnitude and the magnetic field strength.

If the direction of current in a wire is reversed in a uniform magnetic field, what happens to the force? (Higher)

The direction of the force is reversed.

If the strength of the current in a wire is increased in a uniform magnetic field, what happens to the force? (Higher)

The strength of the force is increased.

What criteria must be met for the force = BIL equation to hold? (Higher)

The conductor must be at right-angles to the magnetic field.

What is the unit used for magnetic flux density? (Higher)

Tesla (T).

How does an electric motor work? (Higher)

A coil with current is placed in a magnetic field, and forces on opposite sides of the coil cause rotation.

How do loudspeakers make use of the motor effect? (Higher)

They convert variations in electric current into pressure variations that produce sound.

Explain how a loudspeaker works. (Higher)

A cone with wire is in a magnetic field and connected to an a.c. source. The interaction of fields causes vibration and sound.

How is the pitch of the sound from a loudspeaker changed? (Higher)

Changing the frequency of the a.c. current changes the cone vibration frequency.

What happens when an electrical conductor moves relative to a magnetic field? (Higher)

A potential difference is induced across its ends.

What happens to an electrical conductor when the magnetic field around it changes? (Higher)

A potential difference is induced across its ends.

What must be true for induced potential difference to cause current flow? (Higher)

The conductor must be in a complete circuit.

What can be said about the direction of the field from an induced current? (Higher)

It opposes the change that caused the induction.

How is the generator effect used to create different current types? (Higher)

Alternators for a.c., Dynamos for d.c.

What effect does a microphone use, and how? (Higher)

The generator effect – it converts sound wave pressure into alternating current.

Describe the makeup of a basic transformer. (Higher)

A primary and secondary coil wrapped around an iron core.

Why is iron used in transformer cores? (Higher)

It is easily magnetised.

Explain how a transformer works. (Higher)

An a.c. in the primary coil induces a changing magnetic field in the core, which induces current in the secondary coil.

Why must transformer current be alternating? (Higher)

A changing magnetic field is required to induce current in the secondary coil.

What can be said about power in a 100% efficient transformer? (Higher)

Electrical power input equals electrical power output.