Magnetism and Electromagnetism (AQA GCSE Physics Triple Paper 2)

Question

Answer

What is a magnetic field?

A region where magnetic materials and moving charges experience a force.

What materials are magnetic?

Iron, steel, cobalt, and nickel.

What is a permanent magnet?

A magnet that produces its own magnetic field all the time.

What is an induced magnet?

A material that becomes magnetic when placed in a magnetic field but loses magnetism when the field is removed.

What happens when two like magnetic poles are brought near each other?

They repel.

What happens when two unlike magnetic poles are brought near each other?

They attract.

What is a magnetic field line?

A line that shows the direction of the magnetic force on a north pole; lines go from north to south.

What does the spacing of magnetic field lines show?

Field strength – closer lines mean a stronger field.

Where is the magnetic field around a bar magnet strongest?

At the poles.

What is the Earth’s magnetic field similar to?

A bar magnet tilted slightly from the Earth’s axis.

What is a compass and how does it work?

A small magnet on a pivot; its needle aligns with the Earth’s magnetic field.

What happens when you place a compass near a wire with current?

The needle is deflected due to the wire’s magnetic field.

What causes the magnetic field around a current-carrying wire?

The movement of electric charge in the wire.

What is the shape of the magnetic field around a straight current-carrying wire?

Circular, centred on the wire.

How do you increase the strength of the magnetic field around a wire?

Increase the current or wrap the wire into a coil (solenoid).

What is a solenoid?

A coil of wire; when current flows, it produces a strong and uniform magnetic field inside.

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

It becomes an electromagnet – stronger and switchable.

What is an electromagnet?

A coil of wire with a current, often with an iron core, that acts like a magnet only when current flows.

Give two advantages of electromagnets over permanent magnets.

They can be switched on and off and their strength can be varied.

What is the motor effect?

A force experienced by a current-carrying conductor in a magnetic field.

What factors affect the size of the force in the motor effect?

Size of current, magnetic field strength, and angle between wire and field (maximum at 90°).

In which direction is the force in the motor effect?

Perpendicular to both the magnetic field and current (use Fleming’s Left-Hand Rule).

What does Fleming’s Left-Hand Rule show?

The direction of the force on a conductor in a magnetic field: First finger = Field, seCond finger = Current, thuMb = Motion (force).

What is the condition for the motor effect to occur?

The conductor must be at an angle (not parallel) to the magnetic field.

What is an electric motor?

A device that converts electrical energy into kinetic energy using the motor effect.

How does a basic electric motor work?

A coil in a magnetic field experiences a force that makes it spin; a commutator reverses current to keep rotation.

What is electromagnetic induction?

The creation of a potential difference across a conductor when it moves through a magnetic field or a magnetic field changes around it.

How can you induce a current in a wire?

Move the wire through a magnetic field or change the magnetic field around a coil.

What factors affect the size of the induced potential difference?

Speed of movement, strength of magnetic field, number of coils.

What is the generator effect?

Using electromagnetic induction to produce electricity by moving a conductor in a magnetic field.

What is an alternator?

A generator that produces alternating current (AC).

What is a dynamo?

A generator that produces direct current (DC).

What is the difference between a dynamo and an alternator?

Alternator uses slip rings for AC; dynamo uses a split-ring commutator for DC.

What does a transformer do?

Changes the potential difference of an AC supply (up or down).

What are the two types of transformer?

Step-up (increases voltage) and step-down (decreases voltage).

How does a transformer work?

AC in the primary coil creates a changing magnetic field in the iron core, which induces a voltage in the secondary coil.

Why do transformers only work with AC?

Because a changing magnetic field is needed to induce a current.

What happens in a step-up transformer?

Secondary coil has more turns, so voltage increases and current decreases.

Why is electrical energy transmitted at high voltage?

To reduce energy loss due to resistance in cables – lower current means less heating.

What happens in a step-down transformer?

Voltage is decreased before entering homes for safety.

What is the role of the National Grid?

To transfer electrical energy efficiently from power stations to consumers.

Why is an iron core used in transformers?

It’s easily magnetised and demagnetised and helps transfer magnetic flux efficiently.

What type of current is used in the National Grid and why?

Alternating current (AC), because transformers require AC to work.

What causes the force in a loudspeaker?

A changing current in a coil creates a changing magnetic field, which interacts with a permanent magnet, causing the cone to move and create sound waves.

How does a microphone work?

Sound waves cause a diaphragm to vibrate, which moves a coil in a magnetic field, inducing a current that matches the sound wave.