A conducting circular loop is placed in a uniform magnetic field of $0.4 \mathrm{T}$ with its plane perpendicular to the field. Somehow, the radius of the loop starts expanding at a constant rate of $1 \mathrm{mm} {\mathrm{s}}^{-1}$. The magnitude of induced emf in the loop at an instant when the radius of the loop is $2 \mathrm{cm}$ will be _______ $\mathrm{\mu V}$.

Hence, the correct answer is 50.