Transformers

Question 1

What does a transformer do?

Answer 1

It changes an alternating voltage from one value to another.

Question 2

What does a transformer consist of?

Answer 2

Two coils of insulated wire wrapped around an iron core.

Question 3

How does a transformer work?

Answer 3

The input voltage is connected to the primary coil and the output voltage is taken from the secondary coil.

Question 4

What are step-up transformers?

Answer 4

Transformers that increase the voltage.

There are more turns on the secondary coil than on the primary coil.

Question 5

What are step-down transformers?

Answer 5

Transformers that decrease the voltage.

There are more turns on the primary coil than on the secondary coil.

Question 6

What is the turns ratio transformer equation?

Answer 6

Np/Ns = Vp/Vs

Question 7

How efficient are transformers?

Answer 7

Transformers are very efficient and we can assume that no energy is wasted at all.

Question 8

What equation can be derived from the idea that no energy is wasted in a transformer?

Answer 8

Vp x Ip = Vs x Is

Power in = power out

Question 9

If the secondary coil has twice as many turns of wire as the primary coil, what will the output voltage be?

Answer 9

Twice the input voltage.

Question 10

What type of current will transformers only work with?

Answer 10

Alternating current.

Question 11

Why will direct current not work with transformers?

Answer 11

Using direct current will create a magnetic field in the core, but it will not be a changing magnetic field, so no voltage will be induced in the secondary coil.

Question 12

As voltage is increased in a step-up transformer, what happens to the current? What equation proves this?

Answer 12

Current is decreased in the same proportion.

P = I x V (power = current x voltage) proves this.

Question 13

Why is the power output of a transformer always less than the power input in reality?

Answer 13

Heat is lost to the environment.

Question 14

Why is electricity produced by alternating current in power stations?

Answer 14

1. It is easy to generate alternating current

2. Transformers will not work with direct current.

Question 15

What is the system called through which electricity is sent to homes and factories?

Answer 15

The National Grid.

Question 16

How is electricity carried throughout the grid?

Answer 16

Electricity is carried along aluminium cables suspended between pylons.

Question 17

Why is aluminium used to carry electricity?

Answer 17

Aluminium has a low density and can be safely suspended from inexpensive, thin pylons.

Question 18

What is the disadvantage of pylons?

Answer 18

Pylons are an eyesore.

Question 19

What are the advantages of pylons?

Answer 19

Pylons provide easy access to cables for maintenance and repair.
Transmission using pylons is cheaper than burying cables underground.

Question 20

Why are transformers used to create a very high voltage?

Answer 20

To minimise energy loss.

Question 21

What does a very high voltage mean?

Answer 21

A very high voltage means a low current.

This means that there is less heat lost to the environment.

Question 22

In a power station, before electricity is passed to overhead power lines, what happens?

Answer 22

A step-up transformer at the power station raises the voltage to 400,000 V.

Question 23

What happens before electricity is supplied to homes and factories?

Answer 23

For homes, a step-down transformer reduces the voltage to 240 V.
For factories, a step-down transformer reduces the voltage to 33,000 V.

Question 24

If voltage goes up by 16 times, what happens to current?

Answer 24

It goes down by 16 times.

Question 25

What are the advantages of less heat loss during transmission?

Answer 25

1. Saves energy

2. Conserves fossil fuels at power stations.