A conducting circular loop is placed in a uniform magnetic field...

Key Idea According to Faraday's second law of electromagnetic induction the induced emf is given by rate of change of magnetic flux linked with the circuit. Here, $B=0.04 \mathrm{~T}$ and $\frac{-\mathrm{dr}}{\mathrm{dt}}=2 \mathrm{mms}^{-1}$ Induced emf, \mathrm{e}=\frac{-\mathrm{d} \phi}{\mathrm{dt}}=\frac{-\mathrm{BdA}}{\mathrm{dt}}=-\mathrm{B} \frac{\mathrm{d}\left(\pi \mathrm{r}^2\right)}{\mathrm{dt}}$=-$\mathrm{B} \pi$2$\mathrm{r} \frac{\mathrm{dr}}{\mathrm{dt}}$Now, if$\mathrm{r}=2 \mathrm{~cm} $$\begin{aligned}\mathrm{e}& =-0.04 \times \pi \times2 \times2 \times10^{-2} \times2 \times10^{-3} \\ & =3.2 \pi \mu \mathrm{V} \end{aligned}$$