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 $10\, cm$ and number of turns $100$, so that the magnet gets demagnetised when inside the solenoid, is

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

Answer 1

Answer: (C)

$B=\mu_{0} \,n \,i $
$\frac{B}{\mu_{0}}=n i $
$3 \times 10^{3}=\frac{N I}{L}=\frac{100 \times i}{10 \times 10^{-2}} $
$I=3 \,A $