MULTIPLE CHOICE QUESTIONS

1. [2081 D] In which of the following medium, the velocity of sound is highest?
   a. Vacuum
   b. Water
   c. Hydrogen
   d. Steel
2. [2080 GIE ‘B’] If the speed of sound in air at 20^oC is 344 m/s, the change in speed for 1^oC change in air temperature is
   a. 0.273 m/s
   b. 0.425 m/s
   c. 0.587 m/s
   d. 0.873 m/s

Answers:

1.d

2.c

THEORETICAL QUESTIONS

New Course

1. [2082] Discuss the effect of temperature and pressure on velocity of sound in a gas.   [2]
2. [2081 GIE ‘A’] Explain the effect of temperature and humidity on the velocity of sound in air. [2]
3. [2081 B/C] What correction was made by Laplace over the Newton’s formula for velocity of sound in a gas? Obtain the corrected formula. [3]
4. [2080 R] Write down the Newton’s formula for the velocity of sound in a gas medium with its discrepancy. [1+1]
5. [2079 GIE A]

1. Discuss the effect of temperature and density of elastic medium on velocity of sound.        [2]
2. What are the assumptions of Newton and Laplace on deriving the formula for velocity of sound in gas? Explain. [3]

Old Course

SHORT ANSWER QUESTION

6. [2074 ‘S’] Velocity of sound in solids is more than that in liquids. Why?
   OR [2073 ‘C’] The velocity of sound in solid is generally greater than that in gas at STP, why? Give reason.
7. [2072 ‘C’] When sound waves travel through a medium, does the temperature at various point remain constant? Explain.

LONG ANSWER QUESTION

8. [2078 ‘C’] Explain why sound travels faster in metals than in air. Discuss the effect of temperature, pressure and density of a gaseous medium on velocity of sound.
9. [2076 GIE ‘B’] Discuss Newton’s formula for the velocity of sound in air and explain why and how this formula was modified by Laplace.
10. [2076 ‘B’] Does the propagation of sound wave cause change in thermodynamic condition of medium? Derive Laplace formula of velocity of sound in air.
11. [2075 ‘S’, 2074 ‘A’] Describe Newton’s formula for the velocity of sound in air. Explain why and how this formula is modified by Laplace.
12. [2074 ‘S’, 2073 ‘C’] What correction was made in Newton’s expression for the velocity of sound? Also explain, how change of temperature and pressure affect the velocity of sound.
    OR [2072 ‘S’] Write the Newton’s formula for the velocity of sound in air. Explain why and how this formula is modified by Laplace.
    OR [2072 ‘D’] Write down the Newton’s formula for the velocity of sound in air. Explain why this formula has to be modified. Discuss Laplace’s correction on it.

NUMERICAL PROBLEMS

New Course

1. [2081 B/C] Calculate the wavelength of wave in air at 25^oC if the frequency of sound wave is 256 Hz and velocity of sound at 0^oC is 330 [latex]ms^{-1}[/latex] [2] Ans: 1.35 m

Old Course

2. [2077 ‘D’] At what temperature, the velocity of sound in air is increased by 60% to that at 27^oC? (Ans: 495^oC)
3. [2076 ‘GIE- A’] In a stormy day, a person observes a lightning flash which is followed by a thunder 3 s later. How would you estimate the distance of the lightning flash from the person. (Velocity of sound = 340 m/s, velocity of light = 3 x 10⁸ m/s) Ans: 1020 m
4. [2076 ‘C’] A source of sound of frequency 550 Hz emits waves of wavelength 60 cm in air at 20^oC. What would be the wavelength of sound from the source in air at 0^oC? Ans: 0.579 m
5. [2075 ‘A’] What is the difference between the speed of longitudinal waves in air at 27^oC and at – 13^oC? What is the speed at 0^oC? Ans: 23.94 m/s, 330.693 m/s
6. [2075 ‘B’] At what temperature, the velocity of sound in air is increased by 50% to that at 27^oC? Ans: 402^oC
7. [2073 ‘D’] Calculate the bulk modulus of a liquid in which longitudinal waves with frequency of 250 Hz have the wavelength of 8 m if the density of liquid is 900 kgm^-3. Ans: 3.6 x 10⁹ N/m²
8. [2072 ‘E’] A source of sound produces a note of 512 Hz in air at 17^oC with wavelength 66.5 cm. Find the ratio of molar heat capacities at constant pressure to constant volume at NTP. (Densities of air and mercury at NTP are 1.293 kg/m³ and 13600 kg/m³ respectively). Ans: 1.4
9. A source of sound of frequency 512 Hz emits waves of wavelength 64.5 cm in air at 20^oC. What would be the velocity of sound at 0^oC? Ans: 318.77 m/s
10. In a stormy day, a boy observes a lightning flash which is followed by a thunder 3 sec later. How would you estimate the distance of the lightning strike from the boy? (Given velocity of sound on that day = 332 m/s, velocity of light c = [latex]3\times 10^8[/latex] m/s). Ans: 996 m
11. When a detonator is exploded on a railway line, an observer standing on the rail 2 km away hears two sounds. What is the time interval between them? (Young’s modulus of steel = [latex]2\times 10^{11}\ Nm^{-2}[/latex], density of steel = [latex]8\times 10^3\ kgm^{-2}[/latex], density of air = 1.4 [latex]kgm^{-3}[/latex], [latex]\gamma[/latex] – for air = 1.4, atmospheric pressure = [latex]10^5\ Nm^{-2})[/latex]. Ans: 5.92 s
12. A source of sound of frequency 512 Hz emits waves of wavelength 670 mm in air at 20^oC. What is the velocity of sound in air at this temperature? What would be the wavelength of sound from the source in air at 0^oC? Ans: 343.04 [latex]ms^{-1}[/latex], 0.646 m
13. A man standing at one end of a closed corridor 57 m long blow a short blast on a whistle. He found that the time from the blast to the sixth echo was 2 seconds. If the temperature was 17^oC, what was the velocity of sound at 0^oC? Ans: 331.8 [latex]ms^{-1}[/latex]
14. The interval between the flash of lighting and the sound of thunder is 2 seconds, when temperature is 10^oC. How far is the storm if the velocity of sound in air at 0^oC is 330 [latex]ms^{-1}[/latex]? Ans: 672 m