The induced emf can be produced in a coil by

A) moving the coil with uniform speed inside uniform magnetic field

B) moving the coil with non-uniform speed inside uniform magnetic field

C) rotating the coil inside the uniform magnetic field

D) changing the area of the coil inside the uniform magnetic field

Choose the correct answer from the options given below:

Induced emf is generated due to change in flux linked. 

$\text{ W.K.T. (flux) }\varphi =\overline{B}\cdot \overline{A}=BA\cos \theta$
$\Rightarrow \text{ flux is changed either }\mathrm{B}\text{ (or) A (or) }\theta \text{ (angle between }\overrightarrow{B}\mathrm{\&}\overrightarrow{A}\text{ ) varies with time when }$

$\overrightarrow{B}\text{ changes }\Rightarrow \varphi =BA\cos \theta ,A\cos \theta =\text{ constant }$

$emf=-\frac{d\varphi }{dt}=\left(-\frac{dB}{dt}\right)A\dots ..\mathrm{case}\left(\mathrm{i}\right)$

$\text{ When }\overrightarrow{A}\text{ changes emf }=-B\left(\frac{dA}{dt}\right)\text{.....case(ii) }$

$\text{ When }\theta \text{ changes, emf=}-BA\left(\frac{d\cos \theta }{dt}\right)$

So, in the given question in A & B there are no changes in the above factors.

In C & D we had case (ii) & case (iii) as discussed above

 $\therefore$emf is generated $\Rightarrow$ in option C & D only.