ElectromagnetismElectromagnetism

ELE101/102 Dept of E&E,MIT Manipal 2

Magnetic field around a current carrying conductor

Grip rule : If the conductor is gripped with right hand, with the thumb extended in the direction of current, the fingers wrapped around the conductor indicate the direction of field.

-

+

Magnetic flux

ELE101/102 Dept of E&E,MIT Manipal 3

Magnetic field produced by a solenoid

Field

Grip rule: If the coil (solenoid) is gripped with the right hand, with the fingers pointing in the direction of current, then the thumb out- stretched parallel to the axis of the coil points in the direction of the magnetic field inside the solenoid

ELE101/102 Dept of E&E,MIT Manipal 4

Force acting on a Conductor

A current carrying conductor, placed in a magnetic field, produces a force.

This force can be increased, When the current in the conductor is increased

When length of conductor is increased

When the magnetic field is made stronger

Force on the conductor =

f lux density length of conductor current

or f = B I l Newton

Note: considering single conductor

ELE101/102 Dept of E&E,MIT Manipal 5

Direction of Force: Fleming’s left hand rule

Mechanical force exerted on the conductor always acts in a direction perpendicular to the plane of the conductor and the magnetic field

Field

(Mechanical force)

Current

(Second finger)

thumb

(First finger)

This is the principle of electric motor

ELE101/102 Dept of E&E,MIT Manipal 6

Electromagnetic InductionElectromagnetic Induction

An EMF is induced in a conductor if the following conditions are

satisfied:

Magnetic field

Conductor in the vicinity of magnetic field

Magnetic field linking with conductor changes OR Relative

motion between the Conductor & Field

Faraday’s laws of

Electromagnetic Induction

1) When a conductor cuts or it is cut by

magnetic flux, an emf is induced in the conductor.

2) The magnitude of the induced emf is proportional

to the rate at which the conductor cuts or is cut by

the magnetic fluxI

N

di

dNL

diLdNdt

diL

dt

dNe

ELE101/102 Dept of E&E,MIT Manipal 7

Electromagnetic InductionElectromagnetic Induction

Direction (Polarity) of induced emf:

Lenz’s law:

An electro magnetically induced emf always acts in

such a direction to set up a current opposing the

motion or change of flux responsible for inducing

the emf.

ELE101/102 Dept of E&E,MIT Manipal 8

Fleming's right hand rule

Right hand rule: If the first

finger of the right hand is

pointed in the direction of the

magnetic flux, and if the

thumb is pointed in the

direction of motion of the

conductor relative to the

magnetic field, then the

second finger, held at right

angles to both the thumb and

the first finger represents the

direction of emf.

Field

(First finger)

(thumb)

Motion

(second finger)Emf

ELE101/102 Dept of E&E,MIT Manipal 9

Induced emf

Statically induced emf: - The voltage

induced in the conductor due to change

in the magnetic field

Conductor is stationary

Magnetic Field is changing in a stationary

Magnetic System;

Ex: Transformer

Dynamically induced emf: - The

voltage induced in the conductor due to

relative motion of conductor and

magnetic field

Conductor is moving/stationary

Magnetic Field is stationary/moving sinBlve