(a) Ceiling of good conference halls and concert halls are curved so that the sound waves after reflecting from these walls reaches every part of the hall and can be easily heard by the listeners.
(b) We hear sound produced by the humming bees while that of moving pendulum is not heard. This is because the frequency of vibration of wings of bees is in the audible range of Humans (20Hz to 20 kHz) whereas frequency of vibrations of pendulum is less than 20 Hz so cannot be heard.
(c) Sound waves are mechanical waves as they need material medium for propagation which is the characteristic of the mechanical waves.
(d) We sometimes hear the echo of a sound produced because the distance between the source of the sound and the obstacle is at least 17.2.
(e) People in their old age suffering from hearing loss, wear hearing aids because hearing aid amplifies the electrical signal and converts it into sound which can then be heard much clearly by the old people.
(f) People in their old age suffering from hearing loss, wear hearing aids. This is because hearing aid amplifies the electrical signal and converts it into sound which can then be heard much clearly by the old people.
