A tangent galvanometer shows a deflection of 45° when 10 mA of current is passed through it. If the horizontal component of the earth’s magnetic field is ${\mathrm{B}}_{\mathrm{H}}=\mathrm{\pi }\times {10}^{-6}\mathrm{T}$ and radius of coil is 10 cm, find the number of turns in the coil