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