Magnetic effect of electric current

Oersted’s Experiment

1. Every current carrying conductor has

associated magnetic field and

2. Direction of the magnetic field at a point is

perpendicular to

a. Length of the conductor and

b. The line joining the conductor and the

given point.

Features of Magnetic Field

1. Strength of the magnetic field at a point

near a current carrying conductor is

inversely proportional to the distance of the

point from the conductor.

2. Strength of the magnetic field at a point

near a current carrying conductor is directly

proportional

to the magnitude of current flowing through

the conductor.

3. Direction of the magnetic field at a point

near a current carrying conductor depends

on the direction of the current flowing

through the conductor. If the direction of the

conductor is reversed, direction of the

magnetic field reverses.

Right Hand Rule

‘imagine the current carrying conductor to be

held in your right hand, with the thumb

outstretched and the fingers curled round it. In

this situation, if the thumb indicates the

direction of current, the curled fingers indicate

the direction of the magnetic field around it.’

Magnetic Induction

The vector quantity used to describe the

magnetic field is called magnetic induction (B).

“Magnetic induction at a point is the magnetic

flux density at that point.”

Hence the unit of magnetic induction is

weber/m2 (Wb/m2).

Biot Savart’s Law or Laplace’s Law

The magnitude of magnetic induction at a point neat a current carrying conductor due to small element of the conductor of length dℓ carrying current I, at distance r from the element is directly proportional to a. current I flowing through the element

b. length of the element dℓ c. sine of angle θ between the element and

the line joining the midpoint of the element to the given point and inversely proportional to square of the distance between the midpoint of the element and the given point. The figure shows a conductor carrying current I. According to Biot - Savart’s law the small

magnetic induction dB a P is given as

is a constant whose value is 10 –7 Wb / Am

In vector form

According to right hand rule, the direction of

dB is perpendicular to plane of paper

directed inwards.

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