When two or more waves meet, they superpose or combine at a particular point. The waves are said to interfere. This phenomenon is called interference.
When two pulses meet, they superpose. The resulting pulse has a bigger amplitude which is equal to the vector sum of the amplitudes of the individual pulses. This is called constructive interference.
If the pulses that combine are same amplitude but are out of phase, the resultant amplitude is zero. This is called destructive interference.
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