Wave on String & Sound Wave - NEET Previous Year Questions with Complete Solutions

Waves typically contributes 2 to 3 questions in NEET Physics, worth 8 to 12 marks. Based on NTA question papers from 2015 to 2023, Doppler effect and standing waves on strings appear most consistently. Solving 5–7 years of PYQs from this chapter covers the vast majority of patterns NTA repeats.

Wave on String is moderate in difficulty. The formulas are limited, but NTA tests conceptual understanding — especially around harmonics, resonance conditions, and the effect of changing tension or linear density. Students who understand the physics behind v = √(T/μ) rather than memorising it find this chapter straightforward.

The formula is f′ = f × (v ± v₀) / (v ∓ vₛ), where v is the speed of sound, v₀ is the observer's speed, and vₛ is the source's speed. Use the upper sign (+ for observer, − for source) when motion is toward each other, and the lower sign when moving apart. Always define your positive direction first.

Interference is a spatial phenomenon caused by two waves from different paths combining at a point. Beats are a temporal phenomenon caused by two sources of slightly different frequencies — the resultant amplitude fluctuates periodically at a rate equal to |f₁ − f₂|. They are related concepts but not the same, and NTA sometimes uses this distinction to construct trap options.

Open pipes support all harmonics (1st, 2nd, 3rd…). Closed pipes support only odd harmonics (1st, 3rd, 5th…). A simple memory cue: "Open = all, Closed = odd." The fundamental frequency of a closed pipe of the same length is half that of an open pipe, because only a quarter wavelength fits in the closed pipe at resonance.