Question

A vibrating body produces sound. However no sound is heard when a simple pendulum oscillates in air. Why?

• A. Frequency of vibration of pendulum is very high.
• B. Frequency of vibration of pendulum is more than 20 Hz
• C. Frequency of vibration of pendulum is less than 20 Hz
• D. Frequency of vibration of pendulum is exactly equal to 20 Hz.

Answer 1

The correct option is C Frequency of vibration of pendulum is less than 20 Hz

Sound is heard only if the body vibrates with a frequency of at least 20 Hz. Frequency of vibration of the pendulum is less than 20 Hz. Hence no sound is heard when the pendulum vibrates or oscillates in air.