JEE PYQ: Magnetic Effects Of Current Question 18
Question 18 - 2020 (04 Sep 2020 Shift 2)
A circular coil has moment of inertia $0.8$ kg m$^2$ around any diameter and is carrying current to produce a magnetic moment of $20$ Am$^2$. The coil is kept initially in a vertical position and it can rotate freely around a horizontal diameter. When a uniform magnetic field of $4$ T is applied along the vertical, it starts rotating around its horizontal diameter. The angular speed the coil acquires after rotating by $60°$ will be:
(1) $10$ rad s$^{-1}$
(2) $10\pi$ rad s$^{-1}$
(3) $20\pi$ rad s$^{-1}$
(4) $20$ rad s$^{-1}$
Show Answer
Answer: (1) $10$ rad s$^{-1}$
Solution
Energy conservation: $\frac{1}{2}(0.8)\omega^2 = 20 \times 4 \times (1 - \cos 60°) = 40$. $\omega = 10$ rad/s.
BETA
