Q 12-05-034JEE MainJEE Main 2024 (8 Apr, Shift 2)Easy
The coercivity of a magnet is $5\times10^3\ \text{A/m}$. The amount of current required to be passed in a solenoid of length $30\ \text{cm}$ and number of turns 150, so that the magnet gets demagnetised when inside the solenoid, is ______ A.
Numerical value type. Enter your answer.
Answer: 10
The solenoid must produce $H = nI$ equal to the coercivity, with $n = \dfrac{150}{0.3} = 500\ \text{m}^{-1}$:
$$I = \frac{5\times10^3}{500} = 10\ \text{A}$$
Solution by Sreeraj P, M.Sc Physics