What is the function of the commutator in an
electric motor?
a. it decreases the current in the coil.
b. it reverses the current in the coil.
c. it reverses the poles of the permanent
magnet.
d. it weakens the field of the permanent
magnet.

At 20∘c, the hole in an aluminum ring is 2.800 cm in diameter. you need to slip this ring over a steel shaft that has a room-temperature diameter of 2.804 cm . 1. to what common temperature should the ring and the shaft be heated so that the ring will just fit onto the shaft? coefficients of linear thermal expansion of steel and aluminum are 12×10−6 k−1 and23×10−6 k−1 respectively.