Stationary waves result from wave interference

Steps:

• Recall that stationary waves have fixed nodes and antinodes, unlike progressive waves that travel.
• Identify formation: two progressive waves of same frequency and amplitude meet while traveling in opposite directions.
• Apply wave principles: their combination produces interference patterns with no net energy propagation.
• Match to options: select the principle describing this wave addition.

Why C is correct:

• Superposition principle states that the resultant wave is the algebraic sum of two progressive waves, forming standing (stationary) waves when oppositely directed.

Why the others are wrong:

• A: Diffraction explains wave bending around obstacles, not wave combination.
• B: Polarisation restricts vibration direction in transverse waves, unrelated to stationary formation.
• D: Doppler effect describes frequency shifts from relative motion, not wave interference.

Final answer: C