Q. A tangent galvanometer shows a deflection $45{^\circ}$ when $10\ mA$ current passes through it. If the horizontal component of the earth’s field is $3.6 \times 10^{- 5}T$ and radius of the coil is $10\ cm$. The number of turns in the coil is
A) 5700 turns
B) 57 turns
C) 570 turns
D) 5.7 turns
Explanation
(c) $K = \frac{2rB_{H}}{\mu_{0}n}$
or $n = \frac{2rB_{H}}{\mu_{0}K} = \frac{2 \times 0.1 \times 3.6 \times 10^{- 5}}{4\pi \times 10^{- 7} \times 10 \times 10^{- 3}} = \frac{1.8 \times 10^{3}}{3.14} = 570$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.