What are 'beats'? When do they occur ? Explain their use, if any.

Explanation

Two sound waves of nearly same frequency are travelling in the same direction and interfere to produce a regular waxing ( maximum )and waning (minimum ) in the intensity of the resultant sound waves at regular intervals of time is called beats.
It two vibrating bodies have slightly difference in frequencies , beats can occur.
No. of beats can be heard `Delta upsilon = upsilon_(1) - upsilon_(2)`
Importance `:` 1.It can be used to tune musical instruments.
2. Beats are used to detect dangerous gases.
Explanation for tuning musical instruments with beats `:`
Musicians use the beat phenomenon is tuning their musical instruments. If an instruement is sounded against a standard frequency and tuned until the beats disappear. Then the instrument is in tune with the standard frequency.