If we can get magnetism out of electricity, why can - PowerPoint PPT Presentation

Loading...

PPT – If we can get magnetism out of electricity, why can PowerPoint presentation | free to download - id: 401c3f-MjI2Z

The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

If we can get magnetism out of electricity, why can

Description:

... Generators Faraday s Law Faraday s Law of Induction Comment on Lenz s Law Direction of Induced Current ConcepTest: Lenz s Law Slide 19 Self ... – PowerPoint PPT presentation

Number of Views:14
Avg rating:3.0/5.0
Slides: 25
Provided by: LairdK
Learn more at: http://www.ku.edu.np
Category:
Tags:
User Comments (0)
Transcript and Presenter's Notes

Title: If we can get magnetism out of electricity, why can

1
If we can get magnetism out of electricity, why
cant we get electricity from magnetism?
• The answer..
• Electromagnetic induction

2
Transformers
• This is how first experiment by Faraday was done
• He only got a deflection of the galvanometer when
the switch is opened or closed
• Steady current does not make induced emf.

3
Experimental Observation of Induction
This effect can be quantified by Faradays Law
4
Electromagnetic Induction
• Faraday discovered that a changing magnetic flux
leads to a voltage in a wire loop
• Induced voltage (emf) causes a current to flow !!
• Symmetry electricity magnetism
• electric current magnetic field
• magnetic field electric current

5
What does Faradays law say?
• Faradays law says that
• a) an emf is induced in a loop when it moves
through an electric field
• b) the induced emf produces a current whose
magnetic field opposes the original change
• c) the induced emf is proportional to the rate of
change of magnetic flux

6
Faradays Law of Induction
rate of change of flux with time
induced emf
number of loops
• The faster the change, the larger the induced emf
• The induced emf is a voltage

7
(No Transcript)
8
(No Transcript)
9
TYPES OF INDUCED EMF
• Statically induced emf
• Conductor remains stationary and flux linked
with it is changed
• (the current which creates the flux changes i.e
increases or decreases)
• TYPES
• Self induced
• Mutually induced
• Dynamically induced emf
• Field is stationary and conductors cut across it
• Either the coil or the magnet moves.

10
Can we get emf induced in a motionless circuit?
• An induced emf produced in a motionless circuit
is due to
• 1) a static (steady) magnetic field
• 2) a changing magnetic field
• 3) a strong magnetic field
• 4) the Earths magnetic field
• 5) a zero magnetic field

11
Induction in Stationary Circuit
• Switch closed (or opened)
• Current induced in coil B
• Steady state current in coil A
• No current induced in coil B

12
How does a magnetic field change?
• The field can itself be changing in nature
• Either the magnet itself should move or the
conductor should move with respect to each other
• Hence there should be a relative motion between
magnet and the conductor

13
Electric Generators
• Rotate a loop of wire in a uniform magnetic
field
• changing ? ? changing flux ? induced emf
• ?B B A cos ? B A cos(?t)

Rotation ? ?t
14
Faradays Law
• How to change the flux?
• Recall that flux is
• Changing B or A or q will change the flux.

FB ? B A cosq
15
Faradays Law of Induction
rate of change of flux with time
induced emf
number of loops
• Minus sign from Lenzs Law
• Induced current produces a magnetic field which
opposes the original change in flux

16
Comment on Lenzs Law
• Why does the induced current oppose the change in
flux?
• Consider the alternative
• If the induced current reinforced the change,
then the change would get bigger, which would
then induce a larger current, and then the change
would get even bigger, and so on . . .
• This leads to a clear violation of conservation
of energy!!

17
Direction of Induced Current
• Bar magnet moves through coil
• Current induced in coil
• Reverse pole
• Induced current changes sign
• Coil moves past fixed bar magnet
• Current induced in coil
• Bar magnet stationary inside coil
• No current induced in coil

18
ConcepTest Lenzs Law
• If a N pole moves towards the loop from above the
page, in what direction is the induced current?
• (a) clockwise
• (b) counter-clockwise
• (c) no induced current

19
• SELF INDUCTANCE AND MUTUAL INDUCTANCE

20
Self - Inductance
• Consider a single isolated coil
• Current (red) starts to flow clockwise due to the
battery
• But the buildup of current leads to changing flux
in loop
• Induced emf (green) opposes the change

This is a self-induced emf (also called back
emf)
L is the self-inductance units Henry (H)N2/R
PROPERTY OF A COIL DUE TO WHICH IT OPPOSES THE
CHANGE OF CURRENT OR FLUX THROUGH IT SELF
INDUCTANCE
21
(No Transcript)
22
Mutual Inductance
• Consider two neighboring coils
• if current changes in coil 1, an emf is induced
in coil 2
• ? ? B
• B ? I1
• rewrite as

M is the mutual inductance units Henry (H)
23
MUTUAL INDUCTANCE
• Principle of operation of Transformer

24
(No Transcript)
About PowerShow.com