Ele

ctro

magneti

c In

duct

ion

Can a magnet produce electricity?

Mic

hael F

ara

day

An English scientist who was first to prove that a magnet can produce current.

A magnet can produce

electricity!

Duh!

Joseph Henry

What conditions are necessary for a magnet to produce current?

Magnet must be moving or

Wire must be moving

Movement causes changing magnetic field

Changing magnetic field induces current

Ele

ctro

magneti

c In

duct

ion

The phenomenon by which an emf or current induced in a conductor due to change in magnetic field.

What factors affect the nature of emf or current produced?

Direction of motion In or out

Speed of motion Polarity of magnet

coming in

Number of turns

Area of coil

Dir

ect

ion o

f M

oti

on

The direction of the current induced opposes the change producing it

Speed o

f M

oti

on The faster the

movement is, the greater is the induced emf.

Pola

rity

of

magnet

The induced current produces a magnetic field that opposes the one causing it.

Use RHR

Num

ber

of

turn

s The more the number of turns, the greater the emf induced.

Law

s of

EM

in

duct

ion Faraday’s Law

The induced emf across the conductor is equal to the rate at which magnetic flux is cut by the conductor.

Magneti

c Fl

ux

Product of flux density (B) and the area (A), when flux is at right angles to the area.

Ø= BA

Unit: Weber, Wb

A weber is the flux when a unit tesla of magnetic flux density is at right angles to a unit area.

Magneti

c Fl

ux

Linka

ge

Total flux cut by all turns of the coil

Ø= BAN

So f

ar…

EMF = dØ /dt

For single coil EMF = BA/t

For many coils EMF = BAN/t

For a wire EMF = Blx/t

Where l is length of wire and x is distance traveled.

EMF = Blv Where v is the speed

Lenz’

s La

wThe direction of any

induced current is such as to oppose the change that causes it.

There

fore

EMF = - dØ /dt

For single coil EMF = - BA/t

For many coils EMF = - BAN/t

For a wire EMF = - Blx/t

Where l is length of wire and x is distance traveled.

EMF = - Blv Where v is the speed

Exa

mple

1 A straight wire of length 0.2 m moves at a steady speed of 3 ms-1 at right angles to a magnetic field of flux density 0.1 T. What will be the emf induced across the ends of the wire?

Exa

mple

2

A coil of wire having 2500 turns and of area 1 cm2 is placed between the poles of a magnet so that the magnetic flux passes perpendicularly through the coil. The flux density of the field is 0.5 T. The coil is pulled rapidly out of the field in a time of 0.1 s. What average emf is induced across the ends of the coil?

Investigating Lenz’s Law

Uses of EM Induction (Generator)

Transfo

rmer

Use

s of E

M

Inductio

n