Question

Lenz’s law is expressed by the following formula (here e = induced e.m.f., ∅ = magnetic flux in one turn and N = number of turns)
(a) $e=-\varnothing\frac{dN}{dt}$
(b) $e=-N \frac{d\varnothing}{dt}$
(c) $e=- \frac{d}{dt} (\frac{\varnothing}{N})$
(d) $e=N \frac{d\varnothing}{dt}$

Answer 1

according to Lenz's law, induced electromotive force (emf ) is the negative of rate of change of magnetic flux with respect to time.

mathematically, $\xi_{in}=-\frac{d\phi}{dt}$

if e denotes the induced emf

$\phi$ denotes magnetic flux in one turns

N denotes the number of turns .

so, total magnetic flux changes = N$\phi$

then, e = -$\frac{d(N\phi)}{dt}$

but N is constant.

so, e = -N$\frac{d\phi}{dt}$

hence, option (b) is correct choice.