Question

A tangent galvanometer has $28$ turns and radius of the coil $22cm$. When a current of $0.2A$ is passed it gives a deflection of ${45}^0$. Evaluate horizontal component of the Earth's field.

• A. $1.6\times {10}^{-5}T$
• B. $2.6\times {10}^{-5}T$
• C. $1.6\times {10}^{-6}T$
• D. $1.6\times {10}^{-4}T$

Answer 1

The correct option is A $1.6\times {10}^{-5}T$

$i=k\tan \theta$ or $i=\frac{2r{B}_H}{{\mu }_{0}n}\tan \theta$ or
$B_H=\frac{i{\mu }_{0}n}{2r\tan \theta }=\frac{0.2\times 4\pi \times {10}^{-7}\times 28}{2\times 22\times {10}^{-2}}$
$B_H=1.6\times {10}^{-5}T$