Question

exam lesson name: light and sound
exam number: 700699rr
exam guidelines
exam instructions
question 7 of 20 :
select the best answer for the question.

1. if two waves with equal amplitudes and wavelengths travel through a medium in such a way that a particular particle of the medium is at the crest of one wave and at the trough of the other wave at the same time, what will happen to that particle?

a. the particle will move halfway to the crest due to reinforcement.
b. the particle will remain stationary due to interference.
c. the particle will vibrate with double amplitude due to resonance.
d. the particle will cause beats as a result of the wave combination.
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Explanation:

This question is about wave interference. When two waves with equal amplitudes and wavelengths have a particle at the crest of one and the trough of the other, they interfere destructively. Destructive interference occurs when the displacements of the waves are in opposite directions, leading to cancellation. So the particle, being affected by equal and opposite forces (from the two waves), will remain stationary. Option A is incorrect as reinforcement (constructive interference) would require the particle to be at similar positions (both crests or both troughs) of the two waves. Option C is incorrect because resonance is about a system vibrating at its natural frequency due to an external force, not this wave - particle interaction. Option D is incorrect as beats are formed by the interference of waves with slightly different frequencies, not equal wavelengths and amplitudes in this scenario.

Answer:

B. The particle will remain stationary due to interference.