What are the differences between beat and interference? For two waves, if it can be seen that after an interval of time no sound is heard, which option is liable for this incident? One option is interference of sound, and another is beat. I know that beat is one kind of interference. But sometimes I fail to make difference between them. If interference is liable for that incident, how will you explain the action of interference behind this? If I say that beat is not liable for this, what is the reason behind this? 
 A: Beats cannot extinguish sound completely, but destructive interference of two waves of the same frequency and intensity, however in opposition of phase, yes can. Beats are the effect of superposition of waves of different frequencies. Thus, while you listen, sometimes they fit in phase, which increases the total amplitude and thereby increases much the intensity, and sometimes they are in opposition of phase, which diminishes the total amplitude and thereby reduces the intensity down to zero.

The arrow in the pictures indicates the direction of propagation of the sound. The two superposing waves are colored, one in orange, and one in blue. The pictures represent the amplitudes along the propagation direction, at a given instant of time. One can see that for equal frequency and intensity the amplitudes of the two waves are always opposite, s.t. the total will be zero. For different frequencies, the amplitudes are at some positions, opposite and cancel mutually, and at other positions they are equal and interfere constructively. For obtaining the evolution in time at a certain point in space, just consider the two pictures moving in the indicated direction, and passing through the desired point.
A: I would say, with "ordinary" interference, we have an interference pattern in space, whereas with beats, we have an "interference pattern" in time.
