Question

The coil in a tangent galvanometer is $16cm$ in radius. Find the number of turns that should be wound on it, if a current of $4cm$ produces ${45}^{\circ }$ deflection. Horizontal component of Earth's field is $0.36\times {10}^{-4}T$.

• A. $129$
• B. $179$
• C. $229$
• D. $279$

Answer 1

The correct option is C $229$

In a tanget galvanometer

$N\left(\frac{{\mu }_{0}I}{2r}\right)=B_{H}tan\theta$

$N=\frac{B_{H}tan\theta \ast 2r}{{\mu }_{0}I}$

$r=16cm=0.16m$

$I=0.004A$

$\therefore N=\frac{0.36\ast {10}^{-4}tan{45}^{\circ }\ast 2\ast 0.16}{4\pi \ast {10}^{-7}\ast 0.004}$

$=229$ turns (approx)