Wave speed relates wavelength and period linearly for sound in air

Steps:

• Recall wave speed formula: v = λ / T, where λ is wavelength and T is period.
• For sound in air, v is constant at a given temperature.
• Rearrange to λ = v T, showing direct proportionality.
• A graph of λ (P) vs. T (Q) yields a straight line through origin.

Why D is correct:

• Wavelength equals speed times period (λ = v T); with constant v, λ varies linearly with T.

Why the others are wrong:

• A: Intensity proportional to amplitude squared (I ∝ A²), so nonlinear.
• B: Wavelength inversely proportional to frequency (λ = v / f), so hyperbolic curve.
• C: Speed constant for sound in air, independent of frequency.

Final answer: D