JEE PYQ: Magnetism And Matter Question 12
Question 12 - 2019 (12 Apr 2019 Shift 1)
A magnetic compass needle oscillates 30 times per minute at a place where the dip is $45°$, and 40 times per minute where the dip is $30°$. If $B_1$ and $B_2$ are respectively the total magnetic field due to the earth and the two places, then the ratio $B_1/B_2$ is best given by:
(1) 1.8
(2) 0.7
(3) 3.6
(4) 0.46
Show Answer
Answer: (4) 0.46
Solution
$T = 2\pi\sqrt{\frac{I}{MB_h}}$, so $\frac{T_1^2}{T_2^2} = \frac{B_{h2}}{B_{h1}}$. Computing: $\frac{B_1}{B_2} = \frac{9}{8\sqrt{6}} = 0.46$.
BETA
