A bar magnet has coercivity `4xx10^(3) Am^(-1)`. It is desired to demagnetise it by inserting it inside a solenoid `12 cm` long and having `60` turns. The current that should be sent through the solenoid is

Options

A. 2A
B. 4A
C. 6A
D. 8A

Answer

D

Explanation

The bar magnet coercivity ` 4 xx 10^(3)A//m` i.e., it requires a magnetic intensity `H = 4 xx 10^(3)A//m` to get demagnetised. Let I be the current carried by solenoid having n number of turns per metre length, then by definition H = ni
Here, `H = 4 xx 10^(3)` amp turn /m.
`n = (N)/(l) = (60)/(0.12) = 500` turn/m
`therefore i = (H)/(n) = (4xx10^(3))/(500) = 8.0A`