# Topic 13 - Electromagnetic Induction Flashcards

1
Q

13.1P - Explain how to produce an electric current

A

A bar magnet moves in between two magnets and a wire between them.
The bar magnet causes current to flow.

A changing magnetic field induces a potential difference.
A p.d can be induced if a wire is moved in a magnetic field.
The wire usually is made into a coil so more change in magnetic field.

2
Q

13.2 - What are the factors that determine the strength of induced p.d?

A

Turns in the coil of wire.
Magnetic field strength.
How fast the magnetic field changes or wire moves past coil.
If p.d causes current to flow, magnetic field of current is produced to oppose the p.d.

3
Q

13.3P - Explain how EM induction is used to generate AC and DC current

A

Generators consists of a coil of wire rotated in a magnetic field.
Coil turns and a voltage is induced in wire.
Ends of the coil are connected to slip rings.
Electric contact made to external circuit using carbon brushes.
Generators produce alternating current in power stations and in cars.

In a generator, when a commutator switches the connections every half-turn of the coil with the terminals, the wire moves in one direction.
This produces direct current.
A generator with a commutator is a dynamo.

4
Q

13.4P - Explain how microphones work

A

MIcrophones convert pressure variations in sound waves into current in circuits.
Sound waves cause variations in air pressure which makes the diaphragm vibrate.
The diaphragm moves a coil of wire backwards and forwards inducing a p.d

Loudspeakers convert variations in an electrical current into sound waves.
Loudspeakers have a varying current which moves through a coil that has a magnetic field.
This causes a force on the coil which moves backwards and forwards.
The diaphragm vibrates and produce sound waves.

5
Q

13.5 - Explain how current is induced in transformers

A

Transformers work with alternating current so p.d changes.
The current from primary coil creates a continuously changing magnetic field and the iron core carries this field to the secondary coil.
The changing magnetic field induces a changing p.d on secondary coil.

6
Q

13.6 - What are transformers and what do they do?

A

Transformers are made with two coils of insulated wire on an iron core.
It can change the size of an alternating p.d/voltage.

7
Q

13.7P - What equation links p.d and number of turns?

A

p.d across primary coil/p.d across secondary coil = number of turns in primary coil/number of turns in secondary coil

8
Q

13.8/9 - Explain why electricity is transferred using transformers

A

When electrical current flows through wires it gets warm and there is energy wasted in transmission lines.
So these lines transmit higher voltage with lowers the current through it which means higher efficiency.
Power stations produce electricity with low voltage which is changed by transformers before being sent.
Then a step down transformer decreases the voltage in electricity sent to buildings.

9
Q

13.10 - What equation links p.d and current in coils?

A

P.d across primarycurrent in primary coil=p.d across secondary coilcurrent in secondary coil.