Question

What are waxing and waning in the phenomenon of beats? Show that waxing and waning occur periodically.

Answer 1

Hint: The rise in maximum intensity is called the waxing of sound and the minimum intensity of sound is called waning of sound. These two phenomena occur when two of the sound waves interfere together. When the two interfering sound waves are of equal frequencies the resultant phenomenon is termed as beats.

Complete answer:
The phenomenon of superimpose of two waves is known as interference. The beat occurs due to this phenomenon. At some point the amplitude may increase or decrease periodically. Thus the rise in maximum intensity is called the waxing of sound and the minimum intensity of sound is called waning of sound. The interference in case of beats occurs due to the interference of two sound waves of nearly equal frequency. The term beat frequency is the number of beats in a second. The frequency difference between the two waves is the beat frequency.

The phenomenon of beats is used in the case of a sonometer. That is, a beat is heard when a vibrating tuning fork is placed in a sonometer wire in case that the frequencies are equal. This phenomenon is also used in case of some musical instruments also.

Note:
Sound wave is a longitudinal wave. That is, it has both compression and rarefactions. The pulsing sound in beats is due to the rise and fall in intensities. The rise in maximum intensity is called the waxing of sound and the minimum intensity of sound is called waning of sound. These two phenomena occur when two of the sound waves interfere together. When the two interfering sound waves are of equal frequencies the resultant phenomenon is termed as beats.