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Force, Energy &
Communication
Lesson 10 & 11
TRANSFORMERS
Lesson Objectives




Appreciate the role of transformers
Understand how to make and use a
transformer
To be distinguish between a step-up and
step-down transformer.
To understand and be able to use the
transformer equation
NO! Not one of these!
That’s better, one of these!
PHYSICS TEXT BOOK

Turn to page 94
PHYSICS TEXT BOOK

Turn to page 94

Come round the front bench!
Really – they are just too camp!
Transformers

The job of a transformer is to change the
voltage in a circuit.
Transformers



A step down
transformer REDUCES
the voltage in a circuit.
The input voltage is
higher than the output
voltage.
e.g. transformers found
in electrical substations
Transformers



A step up transformer
increases the voltage in
a circuit.
The input voltage is
lower than the output
voltage.
e.g. transformers used
to convert USA voltage
to UK voltage
What a transformer is made of
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

Consists of two coils of wire wrapped around
a soft iron core.
The coil attached to the INPUT voltage is
called the PRIMARY coil
The coil attached to the OUTPUT voltage is
called the SECONDARY coil.
This is a STEP-UP transformer (more coils in the
secondary than primary coil)

Collect an experiment
sheet and carry out
your own investigation
into transformers.
Calculating the output voltage

The output voltage can be calculated using
this formula:
Calculating the output voltage

The output voltage can be calculated using
this formula:
secondary (output) voltage
primary (input) voltage
=
no. of turns on secondary coil
no. of turns on primary coil
Worked example

A transformer has 960 turns on the primary
coil and 16 turns on the secondary coil. The
primary coil is connected to 230V a.c.. What
will be the output?
Worked example


A transformer has 960 turns on the primary
coil and 16 turns on the secondary coil. The
primary coil is connected to 230V a.c.. What
will be the output?
secondary voltage =
16
230 V
960
Worked example
A transformer has 960 turns on the primary
coil and 16 turns on the secondary coil. The
primary coil is connected to 230V a.c.. What
will be the output?
 secondary voltage
=
16
230 V
960
So the secondary voltage = 230 X (16/960)
=

Worked example
A transformer has 960 turns on the primary
coil and 16 turns on the secondary coil. The
primary coil is connected to 230V a.c.. What
will be the output?
 secondary voltage
=
16
230 V
960
So the secondary voltage = 230 X (16/960)
= 3.9 V


Collect “The transformer – data analysis”

Carry out all the exercises on this sheet.

Collect “The transformer – data analysis”

Carry out all the exercises on this sheet.

HW
Complete the questions on the sheet
“TRANSFORMERS” – hand in on Thursday.

Lesson Objectives




Appreciate the role of transformers
Understand how to make and use a
transformer
To be distinguish between a step-up and
step-down transformer.
To understand and be able to use the
transformer equation