Question

When the shaft is transmitting torque, which of the following phenomenon can cause visibility of light in the eyepiece?

(a) Moving eyepiece equal to the lag amount

(b) Moving eyepiece lesser than the lag amount

(c) Moving eyepiece greater than the lag amount

(d) Independent of eyepiece position

The question was posed to me in exam.

This key question is from Bevis Gibson Flash Light Torsion Dynamometer in portion Brakes and Dynamometers of Machine Dynamics

Answer 1

The correct choice is (a) Moving eyepiece equal to the lag amount

For explanation I would say: During transmission of torque by the shaft, the light is not visible as is does not reach the eyepiece however if the eyepiece is moved to the same amount as the lag of the disc, then light can be seen on the eyepiece.