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:

The induced emf is produced when there is a change in magnetic flux through the coil. By Faraday's law: $$\varepsilon = -\frac{d\Phi}{dt}$$

A. Moving the coil with uniform speed inside uniform magnetic field:

The flux through the coil remains constant (same B, same area, same orientation), so no emf is induced. ✘

B. Moving the coil with non-uniform speed inside uniform magnetic field:

Even with non-uniform speed, if the coil remains entirely within the uniform field, the flux doesn't change. No emf is induced. ✘

C. Rotating the coil inside the uniform magnetic field:

Rotation changes the angle between the area vector and B, so $$\Phi = BA\cos\theta$$ changes with time. Emf is induced. ✔

D. Changing the area of the coil inside the uniform magnetic field:

Since $$\Phi = BA$$, changing $$A$$ changes the flux. Emf is induced. ✔

The correct answer is C and D only.