Torque in AC Machines: Why is Theta Same?

[Eng.FA]

hi

i have question related to

torque = force X r = Fr sin (theta)
and
torque = k (Br X Bs) = k BsBr sin (theta)

why does theta the same in both ??

 

[hariteja]

theta is not same in both.because in t=frsin(theta) theta will be 90 degrees considering normal dc motors or synchronous motors.because,net force acts in direction in which rotation is possible,that means only along the tangential direction to the rotoe cylinderical body.