1. Transmitting Electricity

2. Learning Objectives Recall the parts of the national grid.
Describe what a transformer does.
Use the turns ration equation to predict the missing voltage or number of turns.

3. Question
What happens to electricity when it is generated in power stations??

4. The National Grid
All across the UK a network of pylons and cables distribute electricity to our houses.

5. How are transformers used to supply electricity?

6. Transformers
The voltage of an alternating current can be changed using a transformer.
A step-up transformer increases voltage.
A step-down transformer decreases voltage.

7. Why Change Voltage?
Voltage is increased as it is transmitted through the national grid.
High voltage is very dangerous but reduces energy lost through heat.
Voltage is reduced to 230 V before electricity is supplied to homes.

8. To know how an electric current can be generated in a wire.
RULE TO REMEMBER...
High = Low = Less energy wasted as
Voltage Current heat

9. To know how an electric current can be generated in a wire.

10. To know how an electric current can be generated in a wire.
A transformer where the voltage rises is called a step-up transformer

11. To know how an electric current can be generated in a wire.
A transformer where the voltage falls is called a step-down transformer

12. Direct or alternating current?
Because transformers rely on induction (changing fields), they only work with alternating current (a.c.)

13. The Transformer Equation
To know how an electric current can be generated in a wire.
The Transformer Equation =
Primary voltage
Secondary voltage
No. of turns on Primary coil
No. of turns on Secondary coil or Vp Np = Vs Ns

14. To know how an electric current can be generated in a wire.
Example 1
A transformer has 1000 turns on its primary coil and 3000 turns on its secondary. 30 V is applied across the primary coil. What is its output? V

15. To know how an electric current can be generated in a wire.
Example 2
A transformer has 3800 turns on its primary and 100 turns on its secondary coil. Its output voltage is 6 V.
a) Is it a step up or step down transformer?
b) Calculate the input voltage.
c) Explain why this could be suitable for charging a mobile phone.

16. a) It is a step down transformer. b)
c) Mains voltage is 230V so this transformer is suitable for stepping down the voltage to a safe level for charging a mobile phone. V

17. Copy and complete the tableVs Ns = Vp Np
Copy and complete the table
Primary turns Np
Secondary turns Ns
Primary voltage Vp
Secondary voltage Vs
Step up or step down
100 20 3
400
10,000 10 50
240 12
5,000
33,000
11,000

18. Vs Ns = Vp Np
Primary turns Np
Secondary turns Ns
Primary voltage Vp
Secondary voltage Vs
Step up or step down
100 20 15 3
down
400
10,000 10
250 up
1,000 50
240 12
15,000
5,000
33,000
11,000