Magnetics 5 Question 8
8. The coercivity of a small magnet where the ferromagnet gets demagnetised is $3 \times 10^{3} Am^{-1}$. 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
(2014 Main)
(a) $30 mA$
(b) $60 mA$
(c) $3 A$
(d) $6 A$
Show Answer
Answer:
Correct Answer: 8. (c)
Solution:
- For solenoid, the magnetic field needed to be magnetised the magnet.
$$ B=\mu _0 n I $$
where, $n=100, l=10 cm=\frac{10}{100} m=0.1 m$
$\Rightarrow \quad 3 \times 10^{3}=\frac{100}{0.1} \times I \Rightarrow I=3 A$
