1) The coercivity of a small magnet where the ferromagnet gets demagnetised is $3\times 10^{3}Am^{-1}$. The current required to be passed ina solenoid of length 10cm and number of turns 100, so that the magnet gets demagnetised when inside the solenoid is A) 30mA B) 60mA C) 3A D) 6A Answer: Option CExplanation: For solenoid, the magnetic field needed to be magnetised the magnet. $B=\mu_{0}nI$ [where, n=100,I=10cm= $\frac{10}{100}m=0.1m$] $\Rightarrow 3\times 10^{3}=\frac{100}{0.1}\times I$ I=3A
