Take two metal tubes A and B. Keep one end of each tube on a metal plate. Place a wrist watch at the open end of the tube A and interpose a cardboard between A and B. Now at a particular inclination of the tube B with the cardboard, ticking of the watch is clearly heard. The angle of reflection made by the tube B with the cardboard is equal to the angle of incidence made by the tube A with the cardboard.
(i) Whispering gallery :
The famous whispering gallery at St. Paul’s Cathedral is a circular shaped chamber whose walls repeatedly reflect sound waves round the gallery, so that a person talking quietly at one end can be heard distinctly at the other end. This is due to multiple reflections of sound waves from the curved walls.
(ii) Stethoscope :
Stethoscope is an instrument used by physicians to listen to the sounds produced by various parts of the body. It consists of a long tube made of rubber or metal. When sound pulses pass through one end of the tube, the pulses get concentrated to the other end due to several reflections on the inner surface of the tube. Using this doctors hear the patients’ heart beat as concentrated rays.
(iii) Echo :
Echoes are sound waves reflected from a reflecting surface at a distance from the listener. Due to persistence of hearing, we keep hearing the sound for 101th of a second, even after the sounding source has stopped vibrating. Assuming the velocity of sound as 340 ms–1, if the sound reaches the obstacle and returns after 0.1 second, the total distance covered is 34 m. No echo is heard if the reflecting obstacle is less than 17 m away from the source.
This is explained with a rubber bag filled with carbon-di-oxide as shown in Fig. 7.9. The velocity of sound in carbon-di-oxide is less than that in air and hence the bag acts as a lens. If a whistle is used as a source S, the sound passes through the lens and converges at O which is located with the help of flame. The flame will be disturbed only at the point O.
When sound travels from one medium to another, it undergoes refraction.
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(a) 100 m/s (b) 1000 m/s
(c) 200 m/s (d) 2000 m/s
We know that, v = √T/m
Here, m = mass per unit length = ρs
So, v = √T/ρs
= √(1000/10010
10-6)
= 103 m/s
Therefore, from the above observation we conclude that, option (b) is correct.
The main factor which effects the speed of a sound wave is the ____.
(a) amplitude of the sound wave (b) intensity of the sound
(c) loudness of the sound (d) properties of the medium
As a wave travels into a medium in which its speed increases, its wavelength would ____.
(a) decrease (b) increase
(c) remain the same (d) not affected
As a wave passes across a boundary into a new medium, which characteristic of the wave would NOT change?
(a) speed (b) frequency
(c) wavelength (d) wave number
A periodic and repeating disturbance in a lake creates waves which emanate outward from its source to produce circular wave patterns. If the frequency of the source is 2.00 Hz and the wave speed is 5.00m/s then the distance between adjacent wave crests is ___ meter.
(a) 0.200 (b) 0.400
(c) 1.25 (d) 2.50
Many wave properties are dependent upon other wave properties. Yet, one wave property is independent of all other wave properties. Which one of the following properties of a wave is independent of all the others?
(a) wavelength (b) frequency
(c) period (d) velocity
Q.1 | Q.2 | Q.3 | Q.4 | Q.5 |
d |
b |
b |
d |
d |
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