Previous Year Question
Pendulum clocks become slow in summer because
days in summer are large.
of the friction in the coil.
the length of the pendulum increases.
the weight of the pendulum changes.
Correct Answer: C
Detailed Solution
The time period of a simple pendulum is—
Thus, . Therefore, when the length of the pendulum increases, its time period also increases.
During summer, an increase in temperature causes thermal expansion of the pendulum rod, slightly increasing its effective length.
As the length increases, each oscillation takes slightly more time to complete. Therefore, the pendulum completes fewer oscillations in a given amount of real time, causing the clock to lose time.
The linear expansion of the rod can approximately be expressed as—
Thus, when temperature increases, , which consequently increases the time period.
A change in the weight of the pendulum is not responsible because the time period of an ideal simple pendulum does not depend on the mass of the bob.