\(\Delta \phi=(\Delta \mathrm{B}) \mathrm{A}\)

\(\mathrm{B}_{\mathrm{i}}=5000 \mathrm{~T},\)

\(\mathrm{~B}_{\mathrm{r}}=3000 \mathrm{~T}\)

\(\mathrm{~d}=0.02 \mathrm{~m}\)

\(\mathrm{r}=0.01 \mathrm{~m}\)

\(\Delta \phi=(\Delta \mathrm{B}) \mathrm{A}\)

\(=(2000) \pi(0.01)^2=0.2 \pi\)

\(\varepsilon=\mathrm{N}\left(\frac{\Delta \phi}{\mathrm{t}}\right) \Rightarrow 22=\mathrm{N}\left(\frac{0.2 \pi}{2}\right)\)

\(\mathrm{N}=70\)