Why Does Torque Change in a Rotating Coil Even if the Force Remains Constant?

[delsoo]

Homework Statement

for this question, since area of cutting of magnetic field change, so magnetic flux change, f is unchanged . but i don't understand why the torque will change since the force is unchanged, since torque=FORCE X DISTANCE FROM THE ROTATING PIVOT

Homework Equations

The Attempt at a Solution

 

[dauto]

Distance between the line of action of the force and the pivot is changing.

 

[delsoo]

Can you explain.further. I can't see and understand the situation.

 

[TSny]

but i don't understand why the torque will change since the force is unchanged, since torque=FORCE X DISTANCE FROM THE ROTATING PIVOT

Careful. Torque is generally not equal to the product of the force, F, and the distance, r, between the axis of rotation and the point of application of the force. As dauto is pointing out, torque is the product of force and "lever arm", d.