Physics

Problem

A moving-coil galvanometer has a coil of 50 turns, width

2.0\,\text{cm}

and height

1.0\,\text{cm}

. It is suspended in a radial magnetic field of

0.10\,\text{T}

. When a current of

1.0\,\text{mA}

passes through the coil, the deflection produced is

30^{\circ}

. The torsional constant

k

of the suspension fibre (restoring torque per radian) is closest to a)

9.6\times10^{-7}\,\text{N\,m\,rad}^{-1}

9.5\times10^{-6}\,\text{N\,m\,rad}^{-1}

1.9\times10^{-6}\,\text{N\,m\,rad}^{-1}

3.8\times10^{-6}\,\text{N\,m\,rad}^{-1}