Physics - Study Mode
[#806] Which of the following property of sound is affected by change in air temperature?
Correct Answer
(D) Wavelength
Explanation
Solution: The wavelength of sound changes with temperature. This is because the speed of sound changes with the temperature. Since the speed of sound is different at different temperature, this means the wavelength of sound at a given frequency is a variable depending on the speed of sound. For example, the wavelength of a 100 cycle tone in air at 68ºF would be 11.27 feet while the same tone in fresh water at 68ºF would have a wavelength of 48.05 feet.
[#807] The velocity of sound in moist air is more than in dry air because the moist air has
Correct Answer
(A) Less density than dry air.
Explanation
Solution: The density of dry air is more than that of moist air (when moisture is removed from air, its density increases). The speed of sound in a medium is inversely proportional to the square root of its density. Therefore, the speed of sound in moist air is more than that in dry air.
[#808] Which one among the following doesn't have any effect on velocity of sound ?
Correct Answer
(A) Pressure
Explanation
Solution: Air pressure has almost no effect on sound speed. It has no effect at all in an ideal gas approximation, because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out. In an ideal gas, intermolecular gaps are always taken to be very large, regardless of pressure.
[#809] Velocity of sound in air does not change with the change of
Correct Answer
(B) Pressure of air
Explanation
Solution: Air pressure has no effect at all in an ideal gas approximation. This is because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out, leaving only the effect of temperature. Sound usually travels more slowly with greater altitude, due to reduced temperature.
[#810] The propagation of sound waves in a gas involves
Correct Answer
(A) Adiabatic compression and rarefaction
Explanation
Solution: An adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred only as work. Rarefaction is the reduction of an item’s density, the opposite of compression.