Question

A bar magnet has coercivity 6 x 10³ Am^-1. It is desired to demagnetise it by inserting it inside a solenoid 10 cm long and having 40 turns. The current that should be sent through the solenoid is ____________.

Options

• 2 A

• 4 A

• 6 A

• 15 A

Answer 1

A bar magnet has coercivity 6 x 10³ Am^-1. It is desired to demagnetise it by inserting it inside a solenoid 10 cm long and having 40 turns. The current that should be sent through the solenoid is 15 A.

Explanation:

The bar magnet has coercivity 6 x 10³ Am^-1 i.e., it requires a magnetic intensity H = 6 x 10³ Am^-1 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" = 6 xx 10^3  "Am"^-1`

`"n" ="N"/"l"`

` = 40/0.10 `

`= 400  "turn metre"^-1`

`Rightarrow "i" = "H"/"n" `

`= (6 xx 10^3)/400`

` = 15  "A"`