Question

A tangent galvanometer has a coil of 25 turns and radius of 15 cm. The horizontal component of the earth's magnetic field is $3\times {10}^{-5}T$. The current required to produce a deflection of ${45}^0$ in it, is

• A. 0.14 A
• B. 0.29 A
• C. $3.6\times {10}^{-5}A$
• D. 1.2 A

Answer 1

The correct option is B 0.29 A

For a tangent galvanometer, if deflection is $\theta$, then current reading is given by

$i=ktan\theta$

Where, reduction factor of galvanometer

$k=\frac{2r{B}_H}{{\mu }_{0}n}$

(r = radius of coil, n = no.of turns)

$\Rightarrow i=\frac{2r{B}_H}{{\mu }_{0}n}tan\theta$

$\Rightarrow i=\frac{2\times 15\times {10}^{-2}\times 3\times {10}^{-5}}{4\pi \times {10}^{-7}\times 25}tan{45}^0$

$i=0.29A$

Hence, the correct option is (A)