Physics Waves MDCAT 2010
PMDC Verified Question 120 of 125
Two waves of same amplitude are traveling in the same direction and are out of phase, their resultant wave is:
A
Zero
B
Equal to sum of their amplitudes
C
Equal to difference of their amplitudes
D
Equal to half of their amplitude
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Zero
Concept:

When two waves superimpose, their resultant displacement is the algebraic sum of their individual displacements (Principle of Superposition).

Solution:

  • "Out of phase" implies a phase difference of 180\( ^\circ \) (or \( \pi \) radians), meaning the crest of one wave perfectly aligns with the trough of the other.


  • If they have the same amplitude (\( A \)), they perfectly cancel each other out: \( y_{\text{net}} = A + (-A) = 0 \).


  • This is completely destructive interference.


Why other options are incorrect:

Option B describes constructive interference (in-phase waves). Option C is technically correct mathematically (\( A - A = 0 \)), but "Zero" is the direct and standard physical description of the resultant amplitude.

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