Sound is a form of mechanical wave produced by vibrating objects and transmitted through a medium. This topic covers sound waves, echo, resonance, Doppler effect and the characteristics of sound. It is an important topic for Physics and competitive examinations.
In Stethoscope, the sound of the patient's heartbeat reaches the doctor's ears by:
Correct Answer:
(B) Multiple reflection of sound
Stethoscopes work by the principle of multiple reflection of sound. When a doctor or nurse places a stethoscope diaphragm on a patient's chest, sound waves traveling through the patient's body cause the flat surface of the diaphragm to vibrate and because the vibrating object is attached to a tube, the sound waves are channeled in a specific direction. Each wave bounces, or reflects, off the inside walls of the rubber tube, a process called multiple reflection. In this way, each wave, in succession, reaches the ear tips, or rubber nubs on the ends of the device, and finally the listener's eardrums.
Ques: 2
Assertion (A) : A jet aircraft moving at Mach number equal to 1 travel faster at an altitude of 15 km than while moving at Mach number equal to 1 near the sea level.
Reason (R) : The velocity of sound depends on the temperature of the surrounding medium.
Codes:
(A) and (R) are true, and (R) is the correct explanation of
(A).
Correct Answer:
(D)
is false, but (R) is true.
Speed of supersonic bodies is indicated by the Mach number. The Mach number of an airplane is the ratio of the speed of a body to the speed of sound in a particular medium, usually the atmosphere of the earth. As we know that the speed of sound increases with increase in temperature, the speed of sound at higher altitude (15 km above sea level) decreases due to decrease in temperature. Thus, statement (1) is false. The velocity of a sound wave travelling through the air does not vary with the air pressure but depends on the temperature of the air. Thus reason (R) is correct.
Ques: 3
A worker was working on the rail track. A boy at a distance holds his ear near the rail track. This boy was able to hear sound of the blow of workman twice. It is because of:
Correct Answer:
(A) The speed of sound is greater in steel than in air.
The speed of sound is greater in steel than in air, as sound reaches first by rail track and then by air. Therefore, the boy hears the sound twice.
Ques: 4
Which of the following statements is/are true in relation to sound waves?
Statement I: Speed of sound decreases when we go from solid to gaseous state.
Statement II: In any medium as we decrease the temperature, the speed of sound increases.
Statement III: Speed of sound is less in aluminium medium than in glass medium.
Correct Answer:
(C) Only Statement I is true.
The Speed of sound depends upon the nature of medium through which it propagates. Speed of sound is maximum in solids while minimum in gases. Speed of sound is less in glass medium than in aluminum medium. Increase in temperature results to increase in the speed of sound in any medium. Hence, among the given statement, only statement I is true.
Ques: 5
When a sound wave goes from one medium to another, the quantity that remains unchanged is:
Correct Answer:
(A) Frequency
When a sound wave goes from one medium to another, its frequency usually remains the same (because it is like a driven oscillation and maintains the frequency of the original source) while its speed and wavelength are changed. The amplitude of sound is also changed as it decreases with distance from its source.
Ques: 6
When the same tone is played on a sitar and a flute, the sound produced can be distinguished from each other because of the difference in:
Correct Answer:
(C) quality only
Musical sound can differ from each other with respect to the following three characteristics:
Loudness (intensity)
Pitch (shrillness)
quality (timber)
But quality (timber) is that characteristic of a musical sound which enables us to distinguish between two sounds even if they have the same pitch and loudness.
Ques: 7
Assertion (A) : Reverberation mainly feels in large churches and in other large buildings.
Reason (R) : The walls, roof and ground may cause multiple sound reflections.
Code:
(A) and (R) are true, and (R) is the correct explanation of
(A).
Correct Answer:
(A) and (R) are true, but (R) is not the correct explanation of
Reverberation is a result of multiple reflections. A sound wave in an enclosed or semi-enclosed environment (like large church or in other big building) will be broken up as it is bounced back and forth among the reflecting surfaces. Reverberation is an effect which is multiplicity of echoes whose speed of repetition is to be quick for them and to be perceived as separate from one another.
Ques: 8
When T.V. is switched on:
Correct Answer:
(A) Audio and video both start simultaneously.
When T.V. is switched on, audio and video start simultaneously. In old models of television, audio was heard immediately but the video starts as it needs some warm up time. But in modern televisions, audio synchronizer is used to correct this sync error.