A variable air capacitor like the one shown in the photograph on page 759 has a capacitance that changes between 0.02 and 0.12 F as

A variable air capacitor like the one shown in the photograph on page 759 has a capacitance that changes between 0.02 and 0.12 μF as the shaft is rotated through an angle of 180o. A voltage of 100 V is maintained between the capacitor plates. Initially the capacitor is in its minimum capacitance position.

(a) How much work must be done to rotate the shaft to the maximum capacitance position?

(b) The shapes of the plates are designed so that the capacitance is a linear function of rotation angle. How much torque must be applied to rotate the capacitor to hold it in the position corresponding to C = 0.07 μF?