Question

The coercivity of a small magnet where the ferromagnet gets demagnetised is $3\times {10}^{3}A{m}^{-1}$. The current required to be passed in a solenoid of length $10cm$ and number of turns $100$, so that the magnet gets demagnetised when inside the solenoid, is:

• A. $6A$
• B. $30mA$
• C. $60mA$
• D. $3A$

Answer 1

The correct option is D $3A$

Given that,

Solenoid of length $l=10cm$

Number of turns $n=100$

$H=3\times {10}^{3}A{m}^{-1}$

We know that,

$n=\frac{N}{l}$

$I=\frac{H}{n}$

$I=\frac{3\times {10}^3\times 0.1}{100}$

$I=3A$

Hence, the current is $3A$