1. Last lesson - Electromagnetic induction
If a magnet is moved inside a coil an electric current is induced (produced)

2. Electromagnetic induction
A electric current is induced because the magnetic field around the coil is changing.

3. Generator/dynamo
A generator works by rotating a coil in a magnetic field (or rotating a magnet in a coil). A slip-ring commutator produces alternating current (a.c.)

4. COPY this please!

5. Today’s lesson - Transformers5

6. Transformers
A transformer consists of 3 main parts

7. Transformers
A changing current in the primary coil produces a changing magnetic field in the core. This changing magnetic field induces a changing current in the secondary coil.

8. Vp/Vs = Np/Ns Changing voltages
The ratio of the number of turns on the coils equals the ratio of the voltages
Vp/Vs = Np/Ns
# of turns = Ns
# of turns = Np

9. Changing voltages
A transformer where the voltage rises is called a step-up transformer

10. Changing voltages
A transformer where the voltage falls is called a step-down transformer

11. No energy for nothing
However, no new energy is made

12. No energy for nothing
Power in = power out
VpIp = VsIs

13. a.c. only
Because transformers rely on induction (changing fields), they only work with alternating current (a.c.)

14. Why do we need transformers?

15. Why do we need transformers?
Current flowing through wires causes them to get hot and energy is lost.

16. Why do we need transformers?
Keeping the current low means electricity can be transported long distances without losing too much energy.

17. Why do we need transformers?
However, in order to send a large quantity of energy, high voltages are needed.

18. Transmission of Electricity
Step-up
Step-down