Final answer:
The amplitude of the resultant wave when two identical waves with amplitude X interfere constructively is 2X. This is because the principle of superposition states that the resultant displacement is the sum of the individual displacements. Option c is the correct answer.
Step-by-step explanation:
When two identical waves with an amplitude X superimpose in a manner that allows for pure constructive interference, the resulting wave will have an amplitude that is the sum of the amplitudes of each wave. Constructive interference occurs when the crests of two waves align with each other, effectively doubling their individual effects.
In this scenario, since both waves have an amplitude of X, the amplitude of the resultant wave will be 2X. This phenomenon of amplitude addition is due to the principle of superposition, where the resultant displacement at a point is the sum of the displacments from each wave at that point.
Hence, the correct option for the amplitude of the resultant wave, when two identical waves interfere constructively, is (c) 2X.