(i) Define resonant vibrations.

(ii) Which characteristic of sound, makes it possible to recognize a person by his voice without seeing him ?

(i) Resonant vibrations are vibrations of high amplitude which are produced when the natural frequency of vibrations of the vibrating body is equal to the frequency of forced vibration imposed on it.

(ii) Quality (or timbre) is the characteristic of sound that makes it possible to recognize a person by his voice without seeing him.