What is the maximum induced emf in a rotating coil generator?

[sona1177]

Homework Statement

In a rotating coil generator, the magnetic field between the poles of an electromagnet has the magnitude .40T. A circular coil between the poles has 120 turns and radius 4.0 cm. The coil rotates with frequency 5Hz. Find the maximum emf induced in the coil.

Homework Equations

Emf= change in magnetic flux/time

The Attempt at a Solution

Emf=change in magnetic flux/time=NBAcosθ/time. need emf max, so theta=1??
Emf max=NBA/time
Frequency = 1/t
so t =1/Frequency=1/5=.20

N,B, and A are all given in the problem (A = pi r^2). I plugged the numbers into my equation and got 1.21 but that is wrong.

I have used this equation for rectangular loops, why isn't it working here and how do i do it?

thanks

 

[supratim1]

what do you mean by theta = 1?

 

[supratim1]

you need to calculate total flux change/total time in one revolution.

can you tell me what should be the net change in flux in one complete revolution?

 

[ehild]

The change of flux is zero in one revolution. The magnitude of emf is equal to the time derivative of the flux.

ehild

 

[gneill]

Doesn't the flux through the area encompassed by the coil peak twice per revolution?