1. Starter
The equation for electrical power is: Power = Voltage x current Use the equation to explain: -why is electrical power sent down power cables at high voltages

2. P6 – Electricity for Gadgets
Lesson 13 – Transformers
Learning aim: Demonstrate an understanding of what transformers are and how they work

3. Success Criteria Learning Objectives Understand how transformers work.
Describe the construction of a step- up and a step-down transformer.
Explain why transformers work only on a.c.
Use the equation for a transformer.
Recall properties of transformers.
(Grade E-D)
Describe the construction of a transformer and the difference in construction between step-up and step-down. (Grade C)
Explain properties of an isolating transformer (Grade C-A)
Explain why transformers require ac and how they alter current and voltage (Grade C-A)
Use and manipulate the turns ratio equation.(Grade C-A)
   

4. Power stations Generator Transformer Turbine Boiler National Grid5 6
Boiler
National Grid
Cooling tower

5. National Grid

6. What is a transformer? iron core secondary coil primary coil
The voltage of an alternating current can be changed using a device called a transformer.
A transformer contains two coils that are wound around a soft iron core.
iron core
The alternating current in the primary (input) coil produces an alternating magnetic field.
This alternating magnetic field induces an alternating current in the secondary (output) coil.
secondary
coil
primary
coil

7. How does a transformer change voltage?
The voltage induced in the secondary (output) coil depends on the number of turns on the primary and secondary coils.
A step-up transformer has more turns on the secondary coil and so increases voltage.
A step-down transformer has fewer turns on the secondary coil and so decreases voltage.

8. Where are transformers used?
A television needs a very high voltage to operate. It contains a step-up transformer,
which increases the voltage
of the electricity supplied to the television
This outdoor transformer decreases the voltage of the electricity carried by the national grid. It is an example of a step-down transformer

9. We can work out how much a transformer will step up or step down a voltage:
Voltage across secondary (Vs)
No. of turns on primary (Np)
Voltage across primary (Vp)
No. of turns on secondary (Ns) =

10. Transformers
step up or step down ?

11. Words – alternating, magnetic field, induce, step up, voltage
Transformers
Transformers are used to _____ __ or step down _______. They only work on AC because an ________ current in the primary coil causes a constantly alternating _______ ______. This will “_____” an alternating current in the secondary coil.
Words – alternating, magnetic field, induce, step up, voltage
We can work out how much a transformer will step up or step down a voltage:
Voltage across primary (Vp)
No. of turns on secondary (Ns)
Voltage across secondary (Vs)
No. of turns on primary (Np)
18/09/2018

12. Use the transformer equation:HT
A transformer is used to step a p.d. of 230 V down to 10 V. The secondary coil has 60 turns. How many turns are there in the primary coil?
Use the transformer equation:
VP = 230 V, VS = 10 V, NS = 60 turns 60 10 NP =
230 10
230  60 = NP
= 1380 turns

13. Some transformer questions
Primary voltage Vp
Secondary voltage Vs
No. of turns on primary Np
No. of turns on secondary Ns
Step up or step down?
12V
24V
100 ?
400V
200V 20
25,000V
50,000V
1,000
23V
230V
150
200
Step up 10
Step down
Can use for both tiers – step up and down part for LD
2000
Step up
1500
Step up

14. Transformer Question 1 HT
A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920V.
Is it a step-up or step-down transformer?
What is the output voltage?
Step-down
230V

15. Transformer Question 2 HT
A transformer has 100 turns on its primary coil. It has an input voltage of 35V and an output voltage of 175V.
Is it a step-up or step-down transformer?
How many turns are on the secondary coil?
Step-up
500 turns

16. Plenary - Some example questionsHT
Plenary - Some example questions
Primary voltage Vp
Secondary voltage Vs
No. of turns on primary Np
No. of turns on secondary Ns
Step up or step down? 6V
24V
100 ?
400,000V
200V
1,000
25,000V
20,000 20
230V
150
1,500
400 Up
2,000,000
Down 25
Down 23 Up
A transformer increases voltage from 10V to 30V. What is the ratio of the number of turns on the primary coil to the number of turns on the secondary coil?
A step-down transformer has twice as many turns on the primary coil than on the secondary coil. What will be the output (secondary) voltage if the input voltage is 50V?

17. Plenary On white boards write 4 keywords that you would use in explain
How a transformer changes the voltage?
Alternative LD plenary

18. Success Criteria Learning Objectives Understand how transformers work.
Describe the construction of a step- up and a step-down transformer.
Explain why transformers work only on a.c.
Use the equation for a transformer.
Recall properties of transformers.
(Grade E-D)
Describe the construction of a transformer and the difference in construction between step-up and step-down. (Grade C)
Explain properties of an isolating transformer (Grade C-A)
Explain why transformers require ac and how they alter current and voltage (Grade C-A)
Use and manipulate the turns ratio equation.(Grade C-A)
   

19. Transformer Investigation?
No. of turns on primary Np
No. of turns on secondary Ns
Primary voltage Vp
Secondary voltage Vs
Step up or step down? 50 25
2 (around 2 record your value) 2 10
Conclusion

20. Try some class questions