Transforming

Question 1

What does a transformer consists of?

Answer 1

Two coils of wire wound onto an iron core.

Question 2

AC input and output

Answer 2

• The input AC voltage is connected to the primary coil.
• The output AC voltage is obtained from the secondary coil.

Question 3

Step down and step up transformers

Answer 3

• Step-down transformers have more turns on the primary coil.
• Step-up transformers have more turns on the secondary coil.

Question 4

What are isolating transformers used for?

Answer 4

Isolating transformers are used for safety - the water and steam in the bathroom could lead to electrocution or damage to the house wiring system if an ordinary socket is used.

Question 5

How do transformers work?

Answer 5

• The changing current in the primary coil produces a changing magnetic field.
• The changing magnetic field in the core induces a changing voltage in the secondary coil

Question 6

Transformer Eq.

Answer 6

Question 7

What does the isolating transformer have?

Answer 7

• The isolating transformer has the same number of turns on both secondary and primary coil.
• The mains supply is hidden. The output terminals are not live so there is no danger of electrocution if you touch them with wet hands,

Question 8

Energy loss

Answer 8

• When a current passes through a wire, the wire gets hot.
• The transformers coils and overhead power lines of the National Grid get hot and lose energy to the surroundings.

Question 9

What is power?

Answer 9

Power is a measure of how fast energy is transferred.

Question 10

Power loss Eq.

Answer 10

power loss = current² x resistance

Question 11

Electric power in transformers

Answer 11

The electrical power supplied to the primary coil of a transformer depends on the input voltage and current.

Question 12

Input power is given by:

Answer 12

P_p = V_pI_p

Question 13

The output power of the secondary coil is given by:

Answer 13

P_s = V_sI_s

Question 14

100% efficiency

Answer 14

If the transformer is 100% efficient, input power = output power, i.e. V_pI_p =V_sI_s

Question 15

Increasing voltage in a step up transformer.

Answer 15

• In a step-up transformer, increasing the voltage leads to a decrease in current by the same factor.
• This is seems that the Transformers 100% efficient.
  
  • For example, the step-up transformer at the power station increases the voltage by a factor of 16 to 400 kV. This reduces the current in the overhead cables to 1/16 of what it would be if electricity was transmitted at 25,000 V.