Download How transformers work

LO: Understand the uses of electromagnets
Electromagnets
Electromagnets differ from normal magnets in one major way!
They are made by passing an electric current through a wire
that has been wrapped around iron. The current creates a
magnetic field and magnetises the iron core. When the current
is turned off the iron loses its magnetism
LO: Understand the uses of electromagnets
Electric bell
LO: Understand the uses of electromagnets
Circuit breaker
LO: Understand the uses of electromagnets
Electrical relay
LO: Understand the uses of electromagnets
Scrapyard crane
LO: Understand how electromagnets can be used to make things move
The Motor Effect
If a wire carrying a current is
placed into a magnetic field, an
interesting thing happens.
LO: Understand how electromagnets can be used to make things move
Fleming’s left hand rule
LO: Understand how electromagnets can be used to make things move
Electric Motor
An electric motor uses
the motor effect of
electromagnets to create
motion.
• The force on one side
of the wire causes it to
move up
• The force on the other
side of the wire causes
it to move down
• The motor rotates!
LO: Understand how electromagnets can be used to make things move
Electric Motor
Graphite ‘brushes’ are
used to connect the splitring to the battery. This is
used because:
• Graphite is an
excellent conductor
• It causes very little
friction on the
conducting ring
Understand how
generators create
electricity
ALL – State how
electricity can be
created
MOST – Describe how
electromagnetic
induction can be
increased
SOME – Explain
generators work in
detail
KEYWORDS: Electromagnetic induction,
Generator, coil, wire, magnet
LO: Understand how generators create electricity
Electromagnetic induction
Electromagnetic induction is the term used to describe how
electricity is created in a wire. This is ONE of only TWO ways
that humans know how to generate electricity
LO: Understand how generators create electricity
Electromagnetic induction
By moving the magnet within the coil of
wire, current can be induced within the
current. Note, that the current is only
induced when the magnet or coil is
moving!
How can the amount of current induced
be increased?
• Increase the number of coils
• Increase the speed at which the
magnet/coil moves
• Increase the strength of the magnet
LO: Understand how generators create electricity
Electric generators
LO: Understand how generators create electricity
True or false?
Copy the true sentences and change the false sentences
to make them true:
1) Electricity is induced in a wire using a coil of wire and
an electromagnet
2) Electricity can only be generated when a magnet is
stationary within a coil of wire
3) The amount of electricity induced can be decreased
by increasing the speed at which the magnet/coil of
wire moves
4) The amount of electricity induced can be increased by
increasing the number of coils of wire
Understand how
transformers work
ALL – State the function
of step up and step
down transformers
MOST – Explain how
transformers work and
perform transformer
calculations
SOME – Explain why
values from equations
are just an
approximation
KEYWORDS: transformer, core, step up,
Step down, primary, secondary, induced
LO: Understand how transformers work
Step-up and Step-down
Transformers are an essential
part of the national grid. They
help to increase the voltage
after the power station and
help to decrease it again
when it gets to your house.
LO: Understand how transformers work
Transformers
LO: Understand how transformers work
How do transformers work?
Discuss with the people on
your table how transformers
work. Remember the
following:
• They only work with an a.c.
current
• They need to have an iron
core
• They use electromagnetic
induction to work
LO: Understand how transformers work
How transformers work
1. The alternating current in the primary coil makes the iron
core into an electromagnetic
2. As the current is alternating, the magnetic field ‘moves’
and also changes direction
3. This ‘moving’ magnetic field causes a current to be
induced in the secondary coil
4. If the number of coils on the secondary is higher, the
potential difference will increase and it is a step-up
transformer
5. If the number of coils on the secondary is lower, the
Make a flow diagram of
potential difference will decrease and it is a how
step-down
a transformer works
in your book and draw a
transformer
diagram to go with each
stage
LO: Understand how transformers work
Transformer calculations
The following equation links together the voltage and
number of coils in a transformer:
𝑉𝑝
𝑛𝑝
=
𝑉𝑠
𝑛𝑠
Vp = Voltage on primary coil (v)
Vs = Voltage on secondary coil (v)
np = number of turns on primary coil
ns = number of turns on secondary coil
LO: Understand how transformers work
Example question
A transformer has 400 turns on the primary coil and 200 on the
secondary. If the primary voltage is 300v, what will the secondary
voltage be?
LO: Understand how transformers work
Example question
A transformer has 175 turns on the primary coil and 525 on the
secondary. If the secondary voltage is 300v, what will the primary
voltage be?
LO: Understand how transformers work
Transformer efficiency
Transformers are
extremely efficient
devices.
LO: Understand how transformers work
Transformer efficiency
Transformers are usually about 98% efficient. We can
round this up and say that this is approximately 100%.
Therefore, whatever power the device uses, it will output
the same amount of power!
Power in = Power out
LO: Understand how transformers work
Transformer efficiency
Power in = Power out
Vp x Ip = Vs x Is
Vp = Voltage on primary coil (v)
Vs = Voltage on secondary coil (v)
Ip = Current on primary coil (A)
Is = Current on secondary coil (A)
LO: Understand how transformers work
Example question
A transformer has a primary voltage of 30v and a primary current
of 2A. If the secondary voltage is 15v, what will the secondary
current be?
LO: Understand how transformers work
Example question
A transformer has a primary current of 10A. If the secondary
voltage is 2v and the secondary current is 20A, what will the
primary voltage be?
LO: Understand how transformers work
Example questions
1. A transformer a primary current of 30A. If the secondary
voltage is 10v and the secondary current is 2.4A, what will the
primary voltage be?
2. A transformer has a secondary voltage of 15v and a secondary
current of 4A. If the primary voltage is 2v, what will the primary
current be?
3. A transformer has a primary voltage of 3v and a primary
current of 30A. If the secondary current is 1.5A, what will the
primary voltage be?
4. A transformer has 300 turns on the primary coil, a primary
voltage of 20V and a primary current of 5A. If the secondary
coil has 200 turns, calculate the voltage and current on the
secondary coil.