electromagnetism principles and theory with some applications.

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Electromagnetic Induction
4.5.1 Electromagnetic induction
4.5.2 The a.c. generator
4.5.3 Magnetic effect of a current
4.5.4 Force on a current-carrying conductor
4.5.5 The d.c. motor
4.5.6 The transformer

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Magnetic Field Lines
 There are magnetic field lines around every
 Magnet
 Electrical wire (with current flowing through it)
 Anything magnetic in the field will experience a force
Movie
https://youtu.be/NWUgK8W-4JM

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Fields Bar Magnets
handout

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Single Coil of Wire Solenoid

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The Motor Effect 31/12/2023
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor

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The Catapult (Motor) Effect

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Increasing the Size of the Force

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Motor Effect
 If a conductor carrying an electric current moves
through magnetic field lines at right angles it will
experience a force.
 A charged particle will experience the same effect as
the velocity of it will be to replace the current in the
Fleming's left hand rule.
 For a negatively charged particle the answer will be
reversed.

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The Motor Effect recap
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor

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How does an electric motor work?

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DC electric motor simulation

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Would the same strength motor be used in both of these?
How can the strength of an electric motor be increased?
How do we increase motor strength?
 increase the strength of the magnet
 increase the current flowing through the coil
 increase the number of turns on the coil

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Induction
Aim:
•To observe and define induction
•To explain how electricity is generated

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Inducing current in a wire

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What is electromagnetic induction?
 When a conductor (such as a metal wire) is moved
through a magnetic field, it cuts through the field lines,
inducing an EMF in the wire

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 A similar effect occurs if a magnet is pushed into, or taken
out of a coil:
As the magnet moved through the coil, the field lines cut
through the turns on the coil
This induces an emf in the coil

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Current Carrying Wire + Magnetic field = Motion
Motion + Magnetic field = Current in Wire
Changing Magnetic field = Current in wire
If they are at right angles to each other

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Inducing current in a coil

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Induction
Factors Affecting EM Induction
 The size of the induced EMF is proportional to the rate
at which the field lines are cut:
 the EMF will increase if
1. Moving the wire (or magnet) faster
2. Using a stronger magnet (increasing the number of
field lines)
3. Adding more turns to a coil (assuming a coil is being
used, and not just a wire)
4. Using a bigger coil

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Induction
If a magnet is moved near a coil of wire a current is induced in the wire
• Faster motion, bigger current
• Stronger magnet, bigger current
• More turns, bigger current
**** Change direction of motion, change direction of current

Heinrich F.E. Lenz
• Russian physicist
• (1804-1865)
• 1834 Lenz’s Law
• There is an induced current
in a closed conducting loop
if and only if the magnetic
flux through the loop is
changing. The direction of
the induced current is such
that the induced magnetic
field always opposes the
change in the flux.

Right Hand Rule
• If you wrap your
fingers around the
coil in the direction
of the current, your
thumb points
north.

2 Direction of induced current
In both cases, magnet
moves against a force.
Work is done during
the motion & it is
transferred as electrical
energy.
Induced I always flows to oppose the
movement which started it.
b Lenz's law

Example 1
Current induced along a coil
A bar magnet passes through a coil:
(a) Indicate the direction of the induced I in
each case. Explain briefly.
(i) (ii) (iii)

Example 1
(a) Indicate the direction of the induced I. Explain.
(i)
When magnet’s N-pole is moving
into coil,
induced I flows in such a direction as
to produce a N-pole
to oppose the approaching of magnet.
Lenz’s
law
I
S N

Example 1
(ii)
The induced I become zero

I is about to change direction.

Example 1
(iii)
When magnet’s S-pole is leaving the coil,
induced I flows in such a direction as to
produce a N-pole to oppose the leaving of
magnet.
I
N S

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How can motion produce a current?

There is an induced current in a closed conducting loop if and only
if the magnetic flux through the loop is changing. The direction of
the induced current is such that the induced magnetic field always
opposes the change in the flux.

If the field of the bar magnet is already in the loop and the
magnet is removed, the induced current is in the direction that
tries to keep the field constant

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A generator is a device that converts mechanical energy into electrical
energy. It is the opposite of an electric motor.
Power stations use generators to produce
electricity on a large scale.
Mechanical energy is provided by rotating
turbines that can be powered by:
What are Generators?
 high-pressure steam – in coal, oil, gas and nuclear power stations
 wind – in wind turbines
 falling water – in hydroelectric power stations

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How do AC generators work?

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Induction: true or false?

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The voltage of an alternating current can be changed using a device
called a transformer.
The alternating current in
the primary (input) coil
produces an alternating
magnetic field.
What is a transformer?
A transformer contains two
coils that are wound around a
soft iron core.
iron core
primary
coil
secondary
coil
This alternating magnetic field
induces an alternating current
in the secondary (output) coil.

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The voltage induced in the secondary (output) coil depends on the
number of turns on the primary and secondary coils.
How does a transformer change voltage?
A step-up transformer has
more turns on the secondary
coil and so increases voltage.
A step-down transformer has
fewer turns on the secondary
coil and so decreases voltage.

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How are transformers used to supply electricity?

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Transformers
 Transformers are used to change the voltage from the Primary
(input) to the Secondary (output)
 They only work with a.c. (alternating current)
 Input (Primary) Voltage = Number of Primary Turns
Output (secondary) Voltage Number of Secondary Turns
 Example Question:
 Input voltage = 230 V
 Primary turns = 10000
 Secondary turns = 500
 What is the secondary voltage?
Worksheet

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electromagnetism principles and theory with some applications.

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