Question

The coercivity of a small magnet where the ferromagnet gets demagnetized 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 demagnetized when inside the solenoid, is:

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

Answer 1

The correct option is A $3A$

Coercivity refers to the intensity of magnetic fields $\left(B\right)$ where the magnet gets demagnetised

For solenoid we have, $B={\mu }_{0}nI$

(${\mu }_0=$ absolute permeability, $n=$ no. of turns per unit length, $B=$ Magnetic field in solenoid , I= current through each turn)

$\Rightarrow {\mu }_{0}H={\mu }_{0}nI$ ($H=$ intensity of magnetic field)

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

$\Rightarrow I=\frac{3\times {10}^{3}A/m}{\frac{100}{0.1m}}=3A$

So current needed to be passed through solenoid $=3A$