13) Electromagnetic Induction

Question 1

What is a current?

Answer 1

A flow of charge

Question 2

What two ways can induce a potential difference?

Answer 2

Electrical conductor moving in a magnetic field

Changing magnetic field through electrical conductor

Question 3

How does a changing magnetic field through an electrical conductor induce a p.d?

Answer 3

A changing magnetic field is a magnetic field with changing strength
If there is a magentic field through the middle of a coil of wire, it is ‘linked’ with the coil
A chaging magnetic field that is linked with a coil of wire induces a p.d. in that wire

Question 4

What happens when a wire moves near a magnet?

Answer 4

A p.d is induced in the conductor

Question 5

How can induced potential difference be increased? (2)

Answer 5

More coils
Faster movment (magnetic field change)

Question 6

What happens when a wire moves downwards in a horse show magnet?

Answer 6

A p.d is induced in the wire and an electric current flows through the wire
A force acts in the opposite direction to the action inducing the p.d

Question 7

In which direction does a force induced by the motor effect run?

Answer 7

In an opposite direction to the inductive force

Question 8

What is an AC generated by?

Answer 8

A rotating-coil generator

Question 9

How does a rotating-coil generator work?

Answer 9

A coil of wire is rotated inside a fixed magnetic field
When the coil rotates it cuts across the magnetic field lines and a p.d is induced
The induced p.d causes a current to flow in the coil of wire
The faster the coils cuts across lines, the greater the magnitude of the induced p.d

Question 10

What is a DC generated by?

Answer 10

A dynamo

Question 11

How does a dynamo produce a DC?

Answer 11

A coil of wire rotates and the magnet is fixed
The coil rotates, this generates a p.d in one direction
The split-ring commutator reverses the direction of the current every half-turn of the coil. This makes sure that the current is always moving in the same direction to keep the coil rotating

Question 12

When is the potential difference highest in dynamos?

Answer 12

WHen the coil and magnetic field are parallel

Question 13

When is the potential difference 0 in a dynamo?

Answer 13

When the coil is perpendicular to the magnetic field

Question 14

How do microphones work?

Answer 14

The sound waves that hit the microphone make a coil inside a magnet vibrate
The coil vibrates at the same frequency as the sound wave coming in
This induces a p.d and current in the coil

Question 15

What can transformers do?

Answer 15

Change the voltage in wires carrying an AC

Question 16

What are the 3 main parts of a transformer?

Answer 16

Primary coil
Secondary coil
Iron core

Question 17

What is the transformer equation?

Answer 17

voltage across primary coil / voltage across secondary coil = primary coil turns / secondary coil turns

Question 18

What are the 2 types of transformer?

Answer 18

Step up

Step down

Question 19

What are features of a step-down transformer?

Answer 19

Ns < Np
Secondary coil has fewer turns than primary coil
Voltage across secondary coil is less than voltage across primary coil

Question 20

What are features of a step-up transformer?

Answer 20

Ns > Np
Secondary coil has more turns than primary coil
Voltage across secondary coil is greater than the oltage across the primary coil

Question 21

How do transformers work?

Answer 21

An AC p.d is applied to the primary coil
This causes an AC current to flow through the primary coil
The AC current creates a continously changing magnetic field in the iron core of the transformer
The changing magnetic field in the iron core also passes through the secondary coil
The changing magnetic field passing through the secondary coil induces an alternating p.d in the secondary coil

Question 22

What voltage is electricity generated at?

Answer 22

15,000V

Question 23

What voltage is electricity transmitted at?

Answer 23

400,000V

Question 24

What does transmitting energy at higher voltages do?

Answer 24

Reduce energy lost as heat due to resistance in cables

Question 25

What is the equation for power?

Answer 25

power = current x voltage

Question 26

What would a 100% efficient transformer mean?

Answer 26

Power in primary coil = power is secondary coil

Question 27

How do step-up transformers reduce energy loss?

Answer 27

Reduced current in secondary coil reduces energy lost as heat

Question 28

What does a higher current mean for energy loss?

Answer 28

More energy loss