For a moving coil galvanometer, the deflection in the coil is $0.05 \mathrm{rad}$ when a current of $10 \mathrm{mA}$ is passed through it. If the torsional constant of suspension wire is $4.0\times {10}^{-5}\mathrm{Nm}{\mathrm{rad}}^{-1}$ , the magnitude field is $0.01 \mathrm{T}$ and the number of turns in the coil is $200$, the area of each turn ($\mathrm{in} {\mathrm{cm}}^2$) is