Answer:
1. Answer: (a) 720 m/s
Explanation: Here : Length of column = 40cm =0.4m
Frequency of tuning fork = 450Hz
Using the formula n= v/4l
or v =450 × 4 × 0.4v
= 720m/s
2. Answer: (b) Increases
Explanation: Frequency ∝ v/L. Now v and L both increase with temperature but increase of v is much more than the increase of L which is negligible . Thus frequency increases with temperature.
3. Answer: (a) Directly proportional to amplitude of the wave
Explanation: The loudness of a sound wave is determined from its amplitude. While loudness is only associated with sound waves, all types of waves have an amplitude. Waves on a calm ocean may be less than 1 foot high.
4. Answer: (a)Two sources which emit radiation of nearly the same frequency
Explanation: To demonstrate the phenomena of interference, we require two sources which emit radiation of the same frequency and have a definite phase relationship.
5. Answer: (d) Stationary wave
Explanation: The stationary or standing wave is a superposition of two waves of equal amplitude and frequency moving in opposite direction to each other and so there is no movement of the particles of the medium. That’s why there is no transfer of energy in the case of standing waves.
6. Answer: (a) Stationary longitudinal waves
Explanation: In a resonating air column, longitudinal standing waves are formed. A standing wave is formed when two waves of same amplitude and same frequency, moving with same speed but opposite in direction interfere. A standing wave does not propagate in any direction and it oscillates at one place.
7. Answer: (a) Compression with a phase change of p
Explanation: Therefore, a compression which is travelling towards the wall is reflected as a compression in the direction opposite to the wall and a rarefaction incident on the wall is reflected as a rarefaction.
8. Answer: (a) frequency
Explanation: The physical quantity that remain unchanged when a sound wave goes from one medium to another is frequency.
9. Answer: (a) both longitudinal and transverse elastic waves
Explanation: Sound travels in rocks in the form of both longitudinal and transverse waves, but in air, sound travels only in the form of longitudinal waves'.
10. Answer: (a) All of the above
Explanation: The properties of a medium necessary for wave propagation are its elasticity, low resistance and inertia.
11. Answer: (a) Mach number
Explanation: Mach number is defined as the ratio of speed of a body to the speed of sound in air.
12. Answer: (a) both energy and momentum
Explanation: Sound waves transfer both energy and momentum.
13. Answer: (c) Statement-1 is true, Statement-2 is true; Statement-2 is not a correct explanation for statement-1
Explanation: Laplace corrected Sir Newton's formula for velocity of sound in a gas , by saying that ,when sound wave propagates in a gas , change in pressure and volume in compressions and rarefactions is not an isothermal change but an adiabatic change , and we know that in an adiabatic change there is no exchange of heat between gas and surrounding ( air) , therefore statement -1 is true . On the other hand velocity of sound in a gas (or air) is not related with the conductivity of gas as by the relation given by Laplace .
14. Answer: (a) Neither pressure nor density
Explanation: Pressure and density do not change at an anti-node in a stationary wave.
Only amplitude changes.
15. Answer: (a) Speed of sound waves is more
Explanation: Humidity affects the sound waves. Since Humidity contains more water vapour the medium becomes denser. Consequently the sound would travel faster, means frequency increases.
16. Answer: (b) four nodes and three antinodes
Explanation: It is known that when closed pipe vibrates in fundamental mode, there are one node and one antinode. When it vibrates in first overtone, there are two nodes and two antinodes. When it vibrates in second overtone, there are three nodes and three antinodes. When it vibrates in third overtone, there are four nodes and four antinodes.
17. Answer: (a) 3
Explanation: One cycle of up and down vibration for transverse waves on the string is two cycles of string tension increase and decrease. The tension is maximum both at the loops’ maximum up position and again at maximum down position. Therefore, in longitudinal drive mode, since the string tension increases and decreases once per tuning fork vibration, it takes one tuning fork vibration to move the string loop to maximum up position and one to move it to maximum down position. This is two tuning fork vibrations for one up and down string vibration, so the tuning fork frequency is half the string frequency. Hence, the number of loops in longitudinal mode(tuning fork) is half of that of transverse mode(string).
18. Answer: (c) Both light and sound waves
Explanation: The Doppler effect occurs when the motion of wave source and observer is relative. As we know light and sound, both are waves. Thus Dopler effect is applicable to both sound and light waves.
19. Answer: (c) the frequency as heard by him is 600 Hz
Explanation: Since there is no no relative motion between the listener and source, hence actual frequency will be heard by listener.
20. Answer: (d) Will not change
Explanation: The apparent change in the frequency of the source due to a relative motion between the source and observer is known as Doppler's effect. In the given case there is no relative motion between source and observer, since both are at rest, hence frequency of sound heard by the observer will remain unchanged.
21. Answer: (a) The listener is moving towards the source
Explanation: Since apparent frequency is lesser than the actual frequency, hence the relative separation between source and listener should be increasing.
22. Answer: (a) Harmonics present
Explanation: The quality of sound depends upon the number of harmonics present. Due to different number of harmonics present in two sounds, the shape of the resultant wave is also different.
23. Answer: (a) Mosquito
Explanation: Pitch of mosquito is higher among all given options.
24. Answer: (c) Different quality and different intensity
Explanation: The pitch depends upon the frequency of the source. As the two waves have different amplitude, therefore, they having different intensity. while quality depends on a number of harmonics/overtone produced and their relative intensity. Assuming that their frequencies are the same.
25. Answer: (d) maximum at the nodes
Explanation: In a stationary wave strain is maximum at the node because two opposite forces act at the node.
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