The amplification of two waves occurs because of which of the following?
Choose one answer.
a. destructive interference
b. standing interference
c. antinode interference
d. constructive interference

Question

The amplification of two waves occurs because of which of the following?
Choose one answer.
	 a. destructive interference	
	 b. standing interference	
	 c. antinode interference	
	 d. constructive interference

anonymous · Answer

d

kropot72 · Answer

If two waves have equal frequency and amplitude and travel with the same speed in the same direction, the crest of one wave will correspond to the crest of the other and likewise for the troughs provided there is no phase difference between the waves. The resultant amplitude is twice that of either wave alone and the waves are said to interfere constructively. Therefore answer d is the correct choice.

anonymous · Answer

$$S=S1+S2+2\sqrt{S1*S2}*\cos(\alpha); $$

anonymous · Answer

S-intensity

anonymous · Answer

As Vladislav and kropot72 said, the answer is constructive interference. 
When we deal with interference, we see the vector sum of the displacements caused by the interfering waves at a point. To explain it in simple language, if that sum is zero, then we have a case of destructive interference. If it is non-zero, then the result is constructive interference.

vincent-lyon.fr · Answer

though I would not call this phenomenon "amplification" as total energy is conserved in the process.