The transformer

Question 1

What does a transformer do?

Answer 1

increases or decreases alternating p.d

Question 2

Describe the construction of a simple transformer.

Answer 2

a primary circuit, including the a.c power pack, with a primary coil attached to a soft iron core.
a secondary circuit with a secondary coil attached to the soft iron core.

Question 3

How does a transformer work?

Answer 3

1. alternating p.d/current in primary circuit
2. produces an alternating magnetic field in primary coil
3. alternating magnetic field travels in iron core
4. secondary coil cuts the alternating magnetic field
5. induces an alternating p/d/current in secondary circuit

Question 4

What does a step up transformer do?

Answer 4

increases voltage (in secondary circuit), decreases secondary current

Question 5

What does a step down transformer do?

Answer 5

decreases voltage (in secondary circuit), increases secondary current

Question 6

What does Np mean?

Answer 6

number of turns on primary coil

Question 7

What does Ns mean?

Answer 7

number of turns on secondary coil

Question 8

What does Vp mean?

Answer 8

voltage applied to primary coil

Question 9

What does Vs mean?

Answer 9

voltage induced on secondary coil

Question 10

What does Ip mean?

Answer 10

current in primary coil

Question 11

What does Is mean?

Answer 11

current in secondary coil

Question 12

What is the physical difference between a step up and step down transformer?

Answer 12

step up: more turns on secondary coil
step up: less turns on secondary coil

Question 13

How can you find out a missing number of turns in the primary/secondary coil?

Answer 13

Np/Ns = Vp/Vs

Question 14

Vp/Vs =

Answer 14

Np/Ns

Question 15

Primary power =

Answer 15

secondary power

Question 16

Power =

Answer 16

IV

Question 17

Rate of heat energy loss from wires of resistance R:

Answer 17

P = Iˆ2 x R

Question 18

How are transformers used in transmission of electricity?

Answer 18

1. generator carries voltage to step up transformer
2. wire will carry a high voltage and a low current, resulting in low heat loss
3. it will then be brought to a step down transformer so the p.d can be used

Question 19

State the advantages of high-voltage transmission.

Answer 19

• low heat loss (low current)
• most of electrical energy reaches destination
• thin, cheaper, less heavy cables can be used

Question 20

Np/Ns =

Answer 20

Vp/Vs

Question 21

IpVp =

Answer 21

IsVs (100% efficiency)

Question 22

Power input = power output

Answer 22

IpVp = IsVs

Question 23

Why are power losses in cable smaller when voltage is greater?

Answer 23

P = I^2 x R (where R is rate of heat energy loss)

Question 24

Power input =

Answer 24

power output

Question 25

Power =

Answer 25

current x voltage

Question 26

Why is primary power = secondary power?

Answer 26

principle of conservation of energy