what angle we take between magnetic field and plane of loop....discuss the cases when induced emf is zero in a rotating frame

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 90^o

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

Hope it helps you!!

Cheers!!!

angle between is 90 _degree.