Eemf = Ke*w*If

Where If is field current of the motor, w is the angular velocity and Ke is a constant. But from my understanding,

Emf = K*d(BA)/d(t).

But if B is constant under the magnatic field, then as the motor rotates the change in the area field is: A = Area*cos( Φ ) = Area*cos(wt)

So taking the derivative of this equation

Emf = K*B*Area*w*Sin(wt); which is not a constant.:mellow:

Can anyone explain this???