CAIE A-Level Physics 7.1.7 Wave Intensity and Amplitude

Practise relating intensity to power per area and amplitude squared, combining I = P/A with quantitative comparisons of waves and sources.

Exam points

calculate intensity using I = P/A with the relevant source or detector area
use intensity ∝ amplitude² to compare intensities or amplitudes
combine intensity, power, area and amplitude relationships quantitatively

[Maximum number: 2]

A longitudinal sound wave is travelling through a solid. The initial intensity of the wave is $I_{0}$ . The frequency of the wave remains constant and the amplitude falls to half of its original value.

Determine, in terms of $I_{0}$ , the final intensity of the wave.

$I \propto A^{2}$

C1

$I=(1 / 2)^{2} I_{0}$

intensity $=0.25 I_{0}$

A1

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7.1.7—Intensity = power/area and intensity ∝ (amplitude)2 question 1