An indispensable device for any electronic workbench is a variable transformer or variac. Most variacs use a rotating contact to select a certain number of windings on the secondary coil, usually a solenoid in the shape of a toroid like that in Figure P22.88. Both the primary and secondary coils have 800 windings, but the rotor can connect to any of the individual loops of the secondary coil so that the output voltage is “tapped off” in as few as 100 turns on the secondary coil.
(a) If the AC voltage across the primary is 120 V, what are the maximum and minimum voltage outputs from this device?
(b) What is the smallest increment of change in voltage possible?
(c) The dial on the variac needs calibration. What angle of rotation of the contact corresponds to 25 V? Assume the rotation angle varies from 0° (at the minimum output voltage) to 360° (at the maximum output voltage).