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 coercively `4xx10^(3) Am^(-1)` i.e., it requires a magnetic intensity `H=4xx10^(3) Am^(-1)` to get demagnetized. Let I be the current carried by solenoid having n number of turns per metre length, then by definition `H=ni`. Here `H=4xx10^(3) Amp turn metre^(-1)`
`n=N/l=60/0.12=500 turn metre^(-1)`
`implies i=H/n=(4xx10^(3))/500=8.0A`