Lenz’s law is expressed by the following formula (here e = induced e.m.f., $\mathrm{\varphi }$ = magnetic flux in one turn and N = number of turns)

• A

  $\mathrm{e}=-\mathrm{\varphi }\frac{\mathrm{dN}}{\mathrm{dt}}$

• B

  $\mathrm{e}=-\mathrm{N}\frac{\mathrm{d\varphi }}{\mathrm{dt}}$

• C

  $\mathrm{e}=-\frac{\mathrm{d}}{\mathrm{dt}}\left(\frac{\mathrm{\varphi }}{\mathrm{N}}\right)$

• D

  $\mathrm{e}=\mathrm{N}\frac{\mathrm{d\varphi }}{\mathrm{dt}}$