Submitted by : Submitted by :

Juhee MehtaJuhee MehtaClass XII ScienceClass XII Science

Submitted to : Submitted to :

(Dr.) Mrs. Dheera Samar(Dr.) Mrs. Dheera Samar

Electromagnetic InductionMagnetic Flux

surface

AdB

surfaceover constant Bif

coscos

AB

AdBAdBAdBsurface

dAB

surface

dAB

surface

If B is constant

Electromagnetic Induction

surface

AdB

Electromagnetic Induction

surface

AdB

surface

dAB AdB

cos

bdxx

Iac

c

2

0

ac

c x

dxIb

20

Faraday’s Law Last time we ended class by dropping a magnet

through a coil. Let’s do it again.

coil

Electromagnetic Induction

Faraday’s Law This phenomena is called electromagnetic induction

and is described by Faraday’s law. Write Faraday’s law.

In order to understand Faraday’s law we need to understand the concept of magnetic flux. Write the definition of magnetic flux.

m

B d

A

Electromagnetic Induction

dt

tdt

)()(

Faraday’s Law The magnetic flux is exactly like the electric flux we

studied in Gauss’s law. The flux is defined in terms of a vector area dA. Describe the magnitude and direction of this vector.

Electromagnetic Induction

normal to area

dA

The magnitude is the common area and the direction is normal to the area.

Electromagnetic InductionFaraday’s Law

Faraday’s Law

Electromagnetic Induction

Does it make a difference if it is the magnetic moving or the coil? This was a major point in Einstein’s theory of relativity.

Electromagnetic InductionFaraday’s Law What about these two cases?

Electromagnetic InductionFaraday’s Law

Faraday’s Law Show that when you integrate the emf, with respect

to time you get the average change in flux in time t.

ttdttd mmm )()(

Electromagnetic Induction

dt

tdt

)()(

Average value

12

2

1

)(

)(tt

dtt

tf

t

t

Example: Induction stove The pan on the stove is heated by eddy currents

produced by induction.

Electromagnetic Induction

Would this stove work with a ceramic bowl?

Does the surface of the stove get hot?

Application of Faraday’s Law Generator

Electromagnetic Induction

Application of Faraday’s Law Magnetic Recording

Electromagnetic Induction

Electromagnetic Induction

Two types of electric fields. One is created by charge and the other is created by a changing magnetic field.

The Most Important Point of Faraday’s Law

A changing magnetic field produces

or creates an electric field.