Topic 7 - Magnetism and Electromagnetism (GCSE Edexcel Combined Physics Retrieval Questions)

Name 4 magnetic materials.

Iron, Cobalt, Nickel and Steel.

Define a magnetic material.

A material which is not a magnet and will always be attracted to the magnet, regardless of which pole is held close to it

What is a permanent magnet?

A materials that will produce its own magnetic field and not lose its magnetism

What is an induced magnet?

A magnetic material which gains its own magnetic field when placed within a magnetic field. It loses this after being removed.

Define a magnetic field.

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

Which direction to magnetic field lines travel?

North to South

What do uniform magnetic field lines look like?

The magnetic field lines are parallel and the same distance apart

Where is a magnetic field the strongest and how is this shown with field lines?

Near the poles where the field lines are closest together.

How can you plot a magnetic field?

Using plotting compasses.

If a current is travelling upwards in a straight wire, which direction will the magnetic field be around it?

In concentric circles around the wire, anticlockwise.

Describe the magnetic field of a solenoid.

Similar to a bar magnet outside and uniform inside.

How do you increase the size of the magnetic field of a solenoid?

Increase the current, increase the number of coils, add a iron core (to make it an electromagnet).

What is the motor effect?

When a wire with current flowing through it is placed in a magnetic field and experiences a force.

Why does the moror effect happen?

The magnetic field of the wire and the field between the magnets interact.

How can you increase the motor effect?

Increase the current, increase the magnetic field strength of the magnets, place the wire perpendicularly to the magnet's magnetc field

What do your fingers represent in Fleming's left hand rule?

Thumb - Force, First Finger - Magnetic Field (North to South), Middle Finger - Current (Positive to Negative)

Give the equation linking force, magnetic flux density, current and length.

Force = Magnetic Flux Density x Current x Length

What is the unit for magnetic flux density?

Tesla (T)

In a motor, what does a split ring commutator do?

To reverse the current every 180°, so the motor keeps spinning in one direction.

How do you increase the speed of a motor?

Increase the current, increase the magnetic field strength of the magnet, add more turns to the coil.

How do you change the direction of the motor?

Reverse the current direction, reverse the magnetic poles.

What is electromagnetic induction?

A voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it

What is the generator effect?

Electromagnetic induction but with a full circuit so a current can flow.

How do you increase the voltage induced by electromagnetic induction?

Increase speed of magnet/coil, increase number of turns in coil, increase magnetic field strength

What is the difference between direct and alternating current?

DC travels in one direction and AC changes direction.

What is the potential difference and frequency of UK mains electricity?

230V and 50Hz

What are the wires in a plug and what are their corresponding colours?

Live - Brown, Neutral - Blue, Earth - Green and Yellow

What does the live wire in a plug do?

Carries the alternating potential difference from the supply to a circuit

What does the neutral wire in a plug do?

Forms the opposite end of the circuit to the live wire to complete the circuit

What does the earth wire in a plug do?

Provides a low resistance path to the earth to stop the appliance from becoming live

What does a fuse do?

Cut off the flow of electricity to an appliance if the current becomes too large

What is the National Grid?

A network of cables and transformers

What is the difference between step-up and step-down transformers?

Step-up increase voltage and step-down decrease voltage.

Give the equation linking potential difference and current in a transformer.

Vₚ x Iₚ = Vₛ x Iₛ