What angle we take between magnetic field and plane of loop....discuss the cases when induced emf is zero in a rotating frame.
Ans) We know that Magnetic Flux through a given area is given as 

?=B.A= BAcosθ

Let θ=wt, where w is frequency of source

Now, the Induced emf will be zero if:

1. Magnetic field B is zero,

2. Area of the conductor is zero.

3. Angle between Magnetic field and Area Vector is 90o

Also the angle between the Magnetic field and plane of loop is taken as anticlockwise angle or positive angle