# Magnetic Fields and Induced EMFs - PowerPoint PPT Presentation

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## Magnetic Fields and Induced EMFs

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### Magnetic Fields and Induced EMFs Electromagnetic Induction Just as a magnetic field can be formed by a current in a circuit, a current can be produced using an ... – PowerPoint PPT presentation

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Title: Magnetic Fields and Induced EMFs

1
Magnetic Fields and Induced EMFs
2
Electromagnetic Induction
• Just as a magnetic field can be formed by a
current in a circuit, a current can be produced
using an external magnetic field.
• The process of inducing a current in a circuit
with a magnetic field is called electromagnetic
induction

3
But How???
• Remember, a moving charge in a magnetic field
experiences a force.
• Well a charge that is still will also experience
a force if the magnetic field is moving around
it.
• The moving magnetic field causes the force on
charges which will cause them to go around the
circuit with a current.

4
Electromagnetic Induction
• A current can only be produced if the magnetic
field is changing, or what physicist call, a
magnetic flux
• There are three ways that a magnetic flux can be
produced

5
Induced Current method 1
• The circuit is moved into or out of a magnetic
field.
• This is relative, so the magnetic field could be
moving, the circuit could be moving, or both
could be moving.

6
Induced Current method 2
• The circuit is rotated in the magnetic field.
• The strength of a magnetic field is dependent on
the angle to the circuit.
• By rotating the circuit, the strength of the
magnetic field is changing and therefore a
current can be induced.

7
Induced current 3
• The intensity of the magnetic field is varied.
• This change in the strength of the magnetic field
will cause a current to be induced.

8
• The emf produced is proportional to the change in
the magnetic flux per unit of time and the number
of loops in a circuit.
• Or

9
Magnetic Flux
• F is the magnetic flux, or how much magnetic
field is going through an area.
• Picture a hula-hoop in the rain

10
Hula-hooping in the rain
• The harder the rain, the more water that will go
through the hoop.
• The bigger the hula-hoop, the more water that
will go through the hoop.
• Magnetic flux is the same as this. It is a
factor of how much magnetic field there is and
how much room does it have to flow through.

11
What if you turn the hoop?
• Lets say you are hula-hooping around your arm.
Can any rain get through?
• The angle also determines the amount of magnetic
field that can get through.

12
Magnetic Flux
• Therefore
• Where, A is the area of the circuit loop, and B
is the magnetic field strength

13
• In total, Faradays Law is

14
Summary
• The things that effect electromagnetic induction
according to Fardays law are
• 1) The angle between the magnetic field and the
circuit
• 2) The strength of the magnetic field
• 3) The area of the loop of the circuit
• 4) The number of loops in the circuit
• 5) How quickly the magnetic field changes

15
• simulation

16
Lenzs Law
• What direction is the induced current?
• Lenzs Law states
• The magnetic field of the induced current
opposes the change in the applied magnetic field.

17
Right-hand rule 1 Again
• Remember, a current can induce a magnetic field
of its own.
• The current that it induces will oppose the
direction of the magnetic field flux.

18
Example
• A circuit of wire is pulled through a magnetic
field pointed out of the smart board. What is
the direction of the induced current?

19
Solution
• The current induced will be such that it will
create a magnetic field to go back into the smart
board.
• Therefore, the direction of the current will be
clockwise

20
Door Bells
• Ever wonder why there is a small light behind the
button of a door bell??

21
Door bell continued
• Pushing the door bell disrupts the current in the
left circuit.
• This disruption causes there to be a decrease in
the magnetic field in the left circuit.
• According to Fardays law, this decrease in the
left circuit, causes a current to be induced in
the right circuit.

22
Door bell continued
• The induced current causes a magnetic field in
the right circuit directed through the middle to
the coil.
• The iron bar is pushed outwards and hits the
chime.

23
Door Bell