Free Waves MCQs with Answers

21. Mechanical waves cannot travel through outer space because they:

• A. Have low speed in vacuum
• B. Disperse in space due to long wavelength
• C. Lose frequency in the absence of air
• D. Lose transmission without interacting particles

Explanation: A mechanical wave propagates by particles of a medium pushing on their neighbours, so with no particles there is nothing to carry the disturbance and sound simply does not exist in a vacuum. Electromagnetic waves need no medium, which is why light crosses space while sound cannot. The frequency of a wave is set by its source and is not lost.

22. The energy of a simple harmonic oscillation depends upon the

• A. Frequency
• B. Time period
• C. Wavelength
• D. Amplitude

Explanation: This is the option marked correct in the official UHS answer key, and the total energy of a simple harmonic oscillator is proportional to the square of the amplitude, so doubling the amplitude quadruples the energy. Strictly the energy also depends on the square of the frequency, since the expression is half m omega squared A squared, but amplitude is the variable the question is pointing at. The energy stays constant through the cycle, merely exchanging between kinetic and potential forms.

23. If two speakers emit sound at same frequency and phase, maximum loudness occurs when path difference equals:

• A. half a wavelength
• B. one whole wavelength
• C. a quarter of a wavelength
• D. three quarters of a wavelength

Explanation: A path difference of a whole number of wavelengths brings the two waves back into phase so their crests coincide, giving constructive interference and maximum loudness. An odd number of half wavelengths puts them in antiphase and produces a quiet point instead. The Greek symbol for wavelength did not print cleanly in the original paper.