1. “Transformers – Roberts in disguise”
Core Physics – Energy
Exam Date -
“Transformers – Roberts in disguise”
L/O :- To understand how electricity can be transported by the national grid from power stations to homes

2. Quick Quiz - What do you remember from last lesson?
What are the pros and cons of nuclear energy?
How does a coal power station turn the turbine to spin the generator?
What is the equations for working out efficiency?
How do you work out the pay-back time for insulation?
What are the pros and cons of wind energy?
How do storage heaters work? What happens to wasted energy?
How does evaporation help to cool things down?
What are the pros and cons of solar energy
When is solar energy usually used?

3. Why can birds sit on high voltage cables?
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Why can birds sit on high voltage cables?

4. Electricity reaches our homes from power stations through the
The National Grid
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Electricity reaches our homes from power stations through the
National Grid:
Power station
Step up transformer
Step down transformer
Homes
Our houses use electricity at 230 volts
But if the electricity company transported through the power lines at 230 volts they would lose lots of energy as heat because the current would be too high
To prevent this energy loss they use Transformers.

5. Use the transformers to work out how they affect voltage and current
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Use the transformers to work out how they affect voltage and current
Where should the national grid use each type of transformer?
How reproducible is your data? How could you improve it?

6. Step down transformers
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Step up transformers
These have MORE coils on the second side and increase the voltage and decrease the current
Step down transformers
These have LESS coils on the second side and decrease the voltage and increase the current

7. Step down transformers
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Step up transformers
The national grid use
“step- up” transformers to increase the voltage and decrease the current before it goes into the power cables so less energy is lost
Step down transformers
The national grid use
“step-down” transformers to reduce the voltage before it gets into our houses. This is important for safety.

8. Words – induce, step up, voltage
Transformers
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Transformers are used to _____ __ or step down _______. They only work on AC because an Alternating current in the primary coil causes a constantly alternating Magnetic Field. This will “_____” an alternating current in the secondary coil.
Words – 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)

9. Some transformer questions
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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

10. Some example questions
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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
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?

11. What have you learnt? What is a transformer?
What affect do step-up transformers have on the voltage and current?
What affect do step-down transformers have on the voltage and current?
How do the national grid use step-up and step-down transformers