Question

The coil in a tangent galvanometer is 16 cm in radius. If a current of 20 mA is to produce a deflection of $\text{4}{\text{5}}^{\text{o}},$ then the number of turns wound on it, is (Take horizontal component of earths magnetic field $=0.36\times {10}^{-4}T$ and ${\mu }_0=4\pi \times {10}^{-7}Wb{A}^{-1}{m}^{-1}$ )

• A. 229
• B. 458
• C. 689
• D. 916

Answer 1

Answer: (B)

Current in coil of tangent galvanometer $i=\frac{2rH}{{\mu }_{0}n}\tan \theta$ $\Rightarrow$ $n=\frac{2rH}{{\mu }_{0}i}\tan \theta$ $\therefore$ $n=\frac{2\times 16\times {10}^{-2}\times 0.36\times {10}^{-4}}{4\pi \times {10}^{-7}\times 20\times {10}^{-3}}\tan {45}^o$ $=458$