Question

A simple pendulum is hollow from within and its time period is T. How is the time period of pendulum affected when :

1. 1/4 of bob is filled with mercury
2. 3/4 of bob is filled with mercury
3. The bob is completely filled with mercury?

Answer 1

1. When 1/4 of the bob is filled with mercury, the effective length of the pendulum increases, so the time period increases, as T ∝ `sqrt l`.
2. When 3/4 of the bob is filled with mercury, the effective length of the pendulum decreases, so the time period also decreases, as T ∝ `sqrt l`.
3. When the bob is completely filled with mercury, there is no change in the effective length of the pendulum; hence, there is no change in the time period (it remains T).