Electromagnetism

What is the motor effect?

The motor effect is the force experienced by a current

What three things are needed for the motor effect?

A current

Why does the motor effect occur?

The magnetic field around the current

What does Fleming's left

hand rule show?

What does the thumb represent in Fleming's left

hand rule?

What does the first finger represent in Fleming's left

hand rule?

What does the second finger represent in Fleming's left

hand rule?

How does an electric motor work?

A current

What is the purpose of the split

ring commutator?

What is the function of carbon brushes?

They maintain electrical contact with the rotating split

What is an electromagnet?

A temporary magnet produced when current flows through a coil of wire.

How does an electromagnet work?

Current flowing through a coil creates a magnetic field. A soft iron core strengthens the magnetic field.

How can an electromagnet be made stronger?

Increase the current, increase the number of turns in the coil or add a soft iron core.

Why is soft iron used instead of steel in an electromagnet?

Soft iron is easily magnetised and demagnetised, allowing the electromagnet to be switched on and off.

State four uses of electromagnets.

Scrapyard cranes, electric bells, relays and loudspeakers.

What is a permanent magnet?

A magnet that produces its own magnetic field without electricity.

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

A permanent magnet is always magnetic, whereas an electromagnet is only magnetic when current flows. An electromagnet can also be switched on/off and its strength can be changed.

What is magnetic induction?

Magnetic induction is the process of a magnetic material becoming magnetised when placed in a magnetic field.

What is electromagnetic induction?

Electromagnetic induction is the process of generating a potential difference by moving a conductor through a magnetic field or changing the magnetic field around the conductor.

What is induced potential difference?

A voltage generated when a conductor cuts magnetic field lines.

How can the induced potential difference be increased?

Increase the speed of movement, use a stronger magnet or increase the number of turns in the coil.

What is the generator effect?

The production of a potential difference when a conductor moves through a magnetic field.

How does an AC generator produce electricity?

A rotating coil moves through a magnetic field, inducing an alternating potential difference.

Why is the current from a generator alternating current (AC)?

The direction of the induced current changes every half turn of the coil.

What is a transformer?

A device that changes the size of an alternating potential difference.

Why do transformers only work with AC?

AC produces a changing magnetic field, which is needed for electromagnetic induction.

What is the function of the primary coil in a transformer?

It creates a changing magnetic field when alternating current flows through it.

What is the function of the secondary coil in a transformer?

It has a potential difference induced across it by the changing magnetic field.

What is a step

up transformer?

What is a step

down transformer?

Why is electricity transmitted at high potential difference?

A higher potential difference produces a lower current for the same power, reducing energy losses due to heating in the cables.

What equation links transformer voltages and number of turns?

Vp/Vs = Np/Ns

What equation links power, current and potential difference?

Power = Potential Difference × Current (P = VI).

How is electricity generated in a power station?

A turbine spins a generator, rotating a coil in a magnetic field. Electromagnetic induction generates electricity.

What energy transfers occur in a power station?

Energy source → kinetic energy of turbine → kinetic energy of generator → electrical energy.

What is the National Grid?

A network of cables and transformers used to transmit electricity efficiently across the country.

Why is the National Grid efficient?

Step