1. What do all these have in common? What are they used for?

2. Transformers
Learning Outcomes
By the end of this lesson you will be able...
To investigate practically how a transformer works.
To identify some applications of transformers.
Keywords
Transformer, step-up, step-down , c-core

3. ?

4. Electricity is transferred from power stations to homes through the wires and cables of the National Grid.
When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost.

5. To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage.
Power = voltage x current
Power stays the same so....

6. National grid cables and wires
Homes and Schools
230V
Power station
25,000V
Step up transformer
Step down transformer
National grid cables and wires
400,000V

7. The Transformer Principle
AIM: To investigate how the output voltage of a transformer depends upon the number of turns on the secondary coil.
APPARATUS
Electrical power supply set at 2V A.C.
Connecting wires
An A.C. multimeter (to measure the voltage)
Iron C-core with primary coil of 30 turns of wire on it.
Various iron C-cores with 10, 20, 30, 40, 50 and 60 turns of wire
Calculator

8. The Transformer Principle
Primary coil with 30 turns V
Secondary coil with 10, 20, 30, 40, 50 or 60 turns
C-cores 2V
SAFETY
Always switch off the power supply before making any changes to the circuit.

9. The Transformers Principle
Primary Turns
Secondary Turns
Input Voltage / V
Output Voltage /V
Expected Output Voltage / V 30 10
2.0
Leave this column for now

10. The Transformer principle
State the independent, dependent, and all the control variables (remember this from IAAs).
Plot a graph of output voltage (V) (y-axis) against number of turns on secondary coil (x-axis).
Describe how the output voltage depends on the number of turns on the secondary

11. The Transformer principle
Extra challenge: For transformers, which are 100% efficient, the output voltage can be calculated using this equation.
Use this equation to calculate the expected output voltage (empty column on the table)
How does these answers compare with your results?

12. The Transformer principle
If the output voltage is less than the calculated voltage, the transformer is less than 100% efficient.
Come up with ideas why this may be.

13. Applications of transformers
A step up transformer increases the voltage (Point up)
A step down transformer decreases the voltage (Point down)
Decide whether you think the following are step up transformers or step down transformers.
Extra challenge: Explain why.

14. Lap top charger

15. X ray machine

16. Phone charger

17. National Grid

18. Can you think of any other examples?