Transformers

Question 1

What does a transformer do?

Answer 1

changes the size of alternating voltage by having two separate coils with different number of turns

Question 2

What is a transformer made of?

Answer 2

two coils of wire linked by laminated iron core

Question 3

What is the function of iron core?

Answer 3

guide magnetic field between coils

Question 4

Why is the iron core laminated?

Answer 4

so that current is not induced in it which would reduce efficiency

Question 5

How does a transformer work?

Answer 5

-AC current in primary coil produces changing magnetic field in core which travels to secondary coil
This induces alternating p.d. across the ends of the secondary coil

Question 6

p. d. across primary coil
- ———————————– =
p. d. across secondary coil

Answer 6

no. of turns on primary coil
- ————————————–
no. of turns on secondary coil

Question 7

What effect does changing the number of the coils have ?

Answer 7

changes the voltage output

Question 8

What is a step-up transformer?

Answer 8

more coils on secondary coil

increases voltage - reduces current

Question 9

What is a step-down transformer?

Answer 9

less coils on secondary coil

decreases voltage - more current

Question 10

How efficient are transformers?

Answer 10

almost 100% - therefore power output from transformer is almost same as power input

Question 11

Vp x Ip =

Answer 11

Vs x Is

Question 12

What type of transformers are used in the National Grid?

Answer 12

step-up transformer in overhead cables
from 25 kV to 132 kV
- decreases current - less heat loss - more efficient

Question 13

What happens when voltage reaches towns?

Answer 13

step-down transformer is used to decrease voltage to needed supply