a b c d

a

$ \text{magnetic field due to larger circular loop }B = \frac{\mu_0 I}{2R} = \frac{\mu_0 I_0 cos\omega t}{2b} $ $ \text{Induced Emf } \xi = -A \frac{dB}{dt} = \pi a^2 \frac{\mu_0 I_0 \omega sin\omega t}{2b} $