\begin{aligned}
& 2 \pi r=20 \Rightarrow r=10 / \pi=3.182 \mathrm{~m} . \\
& \mathrm{A}=\pi \mathrm{r}^2=100 / \pi=31.83 \mathrm{~m}^2 \text {. } \\
& \varepsilon=A \frac{d B}{d t} \Rightarrow P=\frac{\varepsilon^2}{R} \\
& P=\frac{A^2\left(\frac{d B}{d t}\right)^2}{R} \\
& =\frac{(31.83)^2\left(5 \times 10^{-3}\right)^2}{10} \\
& =2532.7 \times 10^{-6}=2.53 \mathrm{~mW} \\
&
\end{aligned}