Chapter 12 Sound Solutions
Question - 11 : - Distinguish between loudness and intensity of sound.
Answer - 11 : - The loudness depends on energy per unit area of the wave and on the response of the ear but intensity depends only on the energy per unit area of the wave and is independent of the response of the ear.
Question - 12 : - In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature ?
Answer - 12 : -
Sound travels fastest in iron as compared to water and air.
An echo is returned in 3 s. mat is the distance of the reflecting surface from the source, given the speed of sound is 342 m s-1
Question - 13 : - Why are the ceilings of concert halls curved ?
Answer - 13 : - The ceilings of concert halls are curved because sound after reflection from it reaches all the corners of the hall and is audible to each person in the hall.
Question - 14 : - What is the audible range of the average human ear ?
Answer - 14 : - An average human ear can hear sound waves between frequencies 20 Hz to 20,000 Hz.
Question - 15 : - What is the range of frequencies associated with (a) Infra sound ? (b) Ultrasound ?
Answer - 15 : -
(a) Infra sound : Sound waves between the Frequencies 1 and 20 Hz.
(b) Ultrasound : Sound waves of the frequencies above 20,000 Hz.
Question - 16 : - What is sound and how is it produced ?
Answer - 16 : - Sound is mechanical energy which produces a sensation of hearing. When an Object is set into vibrations, sound is produced.
Question - 17 : - Cite an experiment to show that sound needs a material medium for its propagation.
Answer - 17 : - Take an electric circuit which consists of a cell, a switch and an electric bell arranged inside a bell jar, which stands on the platform of an evacuating pump. The switch of the bell is pressed to close the electric circuit. When there is air within the bell jar, sound is heard. Air is now pumped out of the bell jar. When the air is completely removed from the bell jar, no sound is heard as it is obvious from fig. because the medium of air which has to carry energy from the bell to the bell jar is removed. It shows that sound needs material medium for its propagation.
Question - 18 : - Why is sound wave called a longitudinal wave ?
Answer - 18 : - Sound wave is called longitudinal wave because the particles of the medium vibrate in the direction of the propagation of wave.
Question - 19 : - Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a darkroom ?
Answer - 19 : - The characteristic of sound is quality or timbre.
Question - 20 : - Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why ?
Answer - 20 : - Speed of sound is 330 m/sec in air medium at 0┬░C. Whereas speed of light is 3 x 108m/sec. When we compare the speed of light with that of speed of sound, speed of light is greater than that of speed of sound. Therefore thunder is heard a few seconds after the flash is seen.