Transcript Step down transformers

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
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?
Why can birds sit on high voltage cables?
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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.
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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?
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
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.
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 primary (Np)
Voltage across secondary (Vs)
No. of turns on secondary (Ns)
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
?
?
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
?
1) 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?
2) 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?
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