In a moving coil galvanometer, two moving coils $M_{1}$ and $M_{2}$ have the following particulars : $R_{1}=5 \Omega, N_{1}=15, A_{1}=3.6 \times 10^{-3} m^{2}, B_{1}=0.25 T$
$R_{2}=7 \Omega, N_{2}=21, A_{2}=1.8 \times 10^{-3} \mathrm{~m}^{2}, B_{2}=0.50 \mathrm{~T}$
Assuming that torsional constant of the springs are same for both coils, what will be the ratio of voltage sensitivity of $M_{1}$ and $M_{2}$ ?