The coercive force for a certain permanent magnet is 4.0 × 104 A m–1. This magnet is placed inside a long solenoid of 40 turns/cm and a current is passed in the solenoid to demagnetize it completely. Find the current.
Given:
Coercive force for magnet =4.0× 104Am-1
No. of turns per cm inside solenoid=40
No. of turns per m inside the solenoid =4000 turns/m
We know that,
Coercive force is defined by
Coercive force: the value of magnetic intensity (H) needed to make magnetization(I) zero is known as coercive force .
Therefore, magnetic intensity H=4.0× 104Am-1
Magnetic field produced by solenoid at the centre (B) is given by
…(i)
Where,
n=no. of turns per unit length
I=current in the solenoid
μ0=absolute permeability of vacuum
also magnetizing field intensity (H) in the absence of any material is given by
Where
B=net magnetic field
Putting the value of eqn.(i)
Putting the values of n and H
Therefore, current is given by 10A