A current can be produced in a coil of wire .

a. as a core of iron is being thrust through the coil
b. when a magnet rests in the coil
c. when a core of iron rests in the coil
d. as a magnet is being thrust through the coil

The space between two 15-in.-long concentric cylinders is filled with glycerin (viscosity = 8.5 × 10-3 lb·s/ft2). the inner cylinder has a radius of 1 in. and the gap width between cylinders is 0.1 in. determine (a) the torque and (b) the power required to rotate the inner cylinder at 180 rev/min. the outer cylinder is fixed. assume the velocity distribution in the gap to be linear.