1. Electromagnetic Induction & Transformers
Contents
Electromagnetic induction
Transformers

2. Electromagnetic induction
What happens if a magnet is moved into a coil of wire?
A current is induced in the coil when the magnet is moving.

3. Stationary magnet What happens when the magnet is inside the coil?
Nothing! A current is only induced when the magnet is moving.

4. Electromagnetic induction
What happens if the magnet is moved out of the coil of wire?
A current is induced in the coil in the opposite direction.
If the direction of movement is reversed, then the direction of the induced current is also reversed.

5. Inducing current
What will happen if a magnet is moved in and out of a coil of wire repeatedly?
A current will be induced in the coil. When the magnet is moved into the coil, the current will flow in one direction. Then, when the magnet is moved out of the coil, the direction of the current is reversed and flows in the opposite direction.
The induced current is constantly changing direction. What type of current is this?
alternating current

6. Increasing the size of the induced current
What are the four ways in which the (induced) current from an AC generator can be increased?
1. _________________________
2. _________________________
3. _________________________
4. _________________________
faster movement
stronger magnetic field
more coils
larger area of coils

7. Electromagnetic Induction & transformers
Contents
Electromagnetic induction
Transformers

8. Transformers What is a transformer?
Where are transformers used?
What do we call a transformer that increases voltage?
What do we call a transformer that decreases voltage?
A device used to increase or decrease voltage.
In the national grid and household appliances.
A step-up transformer.
A step-down transformer.

9. How does electricity get to your home?
power station
national grid
step-up
transformer
homes, factories,
businesses, etc.
step-down
transformer

10. Why are transformers useful?
When electrical current flows, f______ is generated in the conductor which in turn generates h___.
This heat is wasted e_____. More wasted energy is created at low v_______ than high voltages.
The voltage of the current is increased before it is transferred to the n______ g___, so that less energy is lost. Then, when the current gets to homes, schools or factories, the voltage is stepped d____.
riction
eat
nergy
oltages
ational rid
own

11. Which type of transformer?
Is this a step-up or a step-down transformer?
primary
coil
secondary
coil
This a step-down transformer because there are
less turns in the secondary coil than the primary coil.

12. Which type of transformer?
Is this a step-up or a step-down transformer?
primary
coil
secondary
coil
This a step-up transformer because there are
more turns in the secondary coil than the primary coil.

13. Transformer calculations
The size of the output voltage from a transformer depends on the ratio of the turns on the primary and secondary coils.
This can be calculated using the following formula:
V1 N1
V2 N2 =
In this formula, V is the voltage in a coil and N is the number of turns in that coil.

14. Transformer question (1)
A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920 V.
Is this a step-up or step-down transformer?
What is the output voltage?
step-down
V2 N2
V1 N1 = N2 N1 =
V x V1 50
200 =
V x 920
= V

15. Transformer question (2)
A transformer has 100 turns on its primary coil. It has an input voltage of 35 V and an output voltage of 175 V.
Is this a step-up or step-down transformer?
How many turns are on the secondary coil?
step-up
N2 V2
N1 V1 = V2 V1 =
N x N1
175 35 =
N x 100
= turns