SP8e The National Grid

Question 1

What are transformers used for?

Answer 1

to change the potential difference of an electricity supply.

Question 2

What are transformers?

Answer 2

two coils of insulated wire, wound on a soft iron core.

Question 3

There is no electrical connection between the two coils of wire so how does the secondary wire have a voltage?

Answer 3

Electromagnetic induction means that a voltage in one coil induces a voltage in the second coil.

Question 4

How does the primary coil work?

Answer 4

.it has a constantly changing AC which produces a constantly changing magnetic field, the iron core takes this field to the secondary coil

Question 5

What does reversing the direction of the magnetic field of a transformer do?

Answer 5

reverses the direction of the current, so AC is produced

Question 6

What do step-up transformers do and what do they change about the coils?

Answer 6

.increase voltage
.more turns in secondary coil

Question 7

What do step-down transformers do and what do they change about the coils?

Answer 7

.decrease voltage
.more turns in primary coil

Question 8

What is the turns ratio equation for transformers?

Answer 8

VpNs = VsNp

Question 9

Why do we use transformers? (6)

Answer 9

.significant energy would be wasted as heat in transmission lines
.to keep this to minimum a step-up transfromer increases voltage
.increased voltage = smaller current so less energy transferred

.voltage is reduced by step-down transformer before going into homes and factories
.this is to make it safer
.also to make current large enough to make appliances work