1. Is this a UK mains voltage supply?
300
200
100
emf (V)
Time division (ms) 5 10 15 20 25 30 35 40
-100
-200
-300

4. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.

5. UK Mains Supply Key Points
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
UK Mains Supply
Key Points
In the UK we receive electricity with a r.m.s voltage of 230 V.
This can vary slightly during the day depending on other usage in the national grid. But the variation is 5% at most.
The electricity supplied is in the form of A.C.
The properties of this supply are ideal for transport but not ideal for use in your home

6. Circuit symbol for a transformer
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
What is this?
Circuit symbol for a transformer

7. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Transforming
The p.d. supplied is A.C and has a voltage far too high for the sensitive devices we tend to use in our homes;
Mobile phone PC
Tablets
Anything which requires charging
A transformer is used to change the voltage up or down to a desired value.
For reasons we will see soon transformers require A.C.

8. Both of these mains adapters contain a transformer.
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Both of these mains adapters contain a transformer.
Step-up transformer  Increases V
Step-down transformer  Decreases V

10. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Draw the diagram to show the basic structure of the transformer. You will need to add the following labels;
Input voltage
Output voltage
Many turns
Few turns
Iron (easily magnetised)
Hollow Core V1 V2

11. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Pens down. Listen to the explanation, you will need to summarise it in a few minutes

12. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
A transformer consists of two electromagnets not physically connected. The alternating current in the primary coil causes an changing magnetic field in the iron.

13. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
The changing magnetic field in the iron links to the secondary coils. Here the alternating magnetic field regenerates an alternating current in the secondary coils.

14. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
What is the relationship between the number of turns on each side and the p.d?

15. Transformers change the p.d. of an electrical supply.
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Transformers change the p.d. of an electrical supply.
Transformers can only work with an alternating current.
A step-down transformer decreases the p.d. of the electricity so it is safer to use in our homes
33,000 V AC
230 V
Distribution
Network
Step-Down
Transformer
Home

16. Use the Keywords to write your own explanation (include a diagram):
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Use the Keywords to write your own explanation (include a diagram):
Primary current
Number of turns
Alternating Current
Secondary current
changing magnetic field
Step down / up

17. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Have you said it all?

18. The ratio of turns decides how much the voltage changes
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
The ratio of turns decides how much the voltage changes
e.g. a transformer with 100 turns on the primary side and 200 turns on the secondary side will double the input voltage.
Q’s.
Transformer has 50 turns on primary side and 150 on secondary side. 5V is supplied, what will the output voltage be?
Transformer has 1250 turns on primary side and 25,000 turns on the secondary side. 1.2KV is supplied, what will the output voltage be?

20. Compare the secondary voltage to the primary voltage
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Compare the secondary voltage to the primary voltage
Where would we use one of these?

21. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
A step-up transformer increases the voltage of the electricity produced by a power station.
By increasing the voltage the current is lowered and the power loss is a square of the current. You need to be able to show this mathematically!
25,000 V AC
275,000 V
Power
Station
Step-Up
Transformer
High Voltage
Transmission

22. How does a transformer change voltage?
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
How does a transformer change voltage?
Which will step-up, which will step-down?
Which would you want in your home, which would you want in a power station?

23. NP = number of turns on primary coil
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
The number of turns (loops) in each coil determines whether the potential difference increases (steps up) or decreases (steps down).
Vp = Primary
Voltage
Vs = Secondary
Voltage
NP = number of turns on primary coil
NS = number of turns on secondary coil

24. Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Vs = Secondary
Voltage
Vp = Primary
Vp = 120V, Vs = 12 V. Turns on primary = 10, how many turns are needed on secondary?
Vp = 120V, Vs = 12 V. Turns on primary = 50, how many turns are needed on secondary?
Vp = 10,000V, Vs = 240 V. Turns on secondary 12, how many turns are needed on secondary?

26. And to finish… Complete the question sheet
Specification Aims By the end of this lesson you should be able to…
Explain the basic construction of a transformer and how to set one up in a circuit.
Describe the relationship between the ratio of p.d.’s across the coils to the ratio of the number of turns on each coil.
Explain the conservation of energy and its application to transformers.
Consolidation
And to finish… Complete the question sheet