Download What do all these have in common? What are they - Physics-S3

What do all these have in common?
What are they used for?
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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
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• 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.
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• 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....
• Power = voltage x current
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Power
station
25,000V
Step up
Step down
transformer National grid transformer
cables and
wires
400,000V
Homes
and
Schools
230V
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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
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The Transformer Principle
Primary coil with 30
turns
2V
V
Secondary coil with 10,
20, 30, 40, 50 or 60
turns
C-cores
V
SAFETY
Always switch off the power supply before
making any changes to the circuit.
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The Transformers Principle
Primary
Turns
Secondary
Turns
Input Voltage /
V
30
10
2.0
Output Voltage
/V
Expected
Output
Voltage / V
Leave this
column for now
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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 (xaxis).
• Describe how the output voltage depends on
the number of turns on the secondary
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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?
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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.
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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.
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Lap top charger
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X ray machine
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Phone charger
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National Grid
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Can you think of any other
examples?
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