Question

In Cavendish Experiment, the angle of rotation is measured by the deflection of a light beam reflected from a mirror attached to the vertical suspension. Why?

• A. The deflection of the light is an effective technique for dampening the motion.
• B. The deflection of the light is convenient.
• C. The deflection of the light is an effective technique for amplifying the motion.
• D. None of these

Answer 1

Answer: (C)

The deflection of the light is an effective technique for amplifying the motion.

By keeping the mirror at the suspension and we are able to notice the angle better because let the rod moves by an angle $\theta$ due to the reflection of light on the scale, the difference would be $2\times \theta$ so that we can observe the small change in the angle rotated. It is a method for amplifying the angle in the motion so that it's motion is easily noticed.