The sounds of different people can easily be identified even without having seen them. Identify the characteristics of the sound wave and the factor on which it depends.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Loudness and wave amplitude
Note: The given answer is as per the official NTA Answer Key. However, the answer given by NTA appears to be incorrect: voices are told apart by the quality (timbre) of sound, which depends on the wave form, so Option (4) is the correct answer, as explained below. The question asks who is speaking; NTA’s key answers how loud the voice is.
A musical sound or a voice has three characteristics, and each depends on one feature of the sound wave:
Loudness — depends on the amplitude of the wave
Pitch (shrillness) — depends on the frequency of the wave
Quality or timbre — depends on the wave form, the shape of the wave
Two people may speak equally loudly and at the same pitch, and we still know who is speaking without seeing them. What tells the voices apart is their quality (timbre): each voice mixes its main note with other, weaker notes in its own way, which gives its wave a shape of its own.
Option (1) Quality and wavelength — Incorrect. For a given speed of sound, the wavelength is fixed by the frequency, which decides pitch, not quality.
Option (2) Loudness and wave amplitude — Correct as per NTA; however, it does not identify a voice. Loudness does depend on amplitude, but two voices of the same loudness are still told apart.
Option (3) Quality and wave frequency — Incorrect. Frequency decides the pitch of a sound, not its quality.
Option (4) Quality and wave form — Should have been correct. Quality is the characteristic that identifies a voice, and it depends on the wave form.