Sound — Set 3
Physics · ध्वनि · Questions 21–30 of 60
In humid air compared to dry air at the same temperature, the speed of sound is generally?
Correct Answer: D. Slightly higher
Humid air has a lower average molecular mass than dry air. Lower mass per particle can make sound travel slightly faster at the same temperature. The effect is small but measurable in air.
For a stretched string under the same tension, a longer length generally produces?
Correct Answer: D. A lower pitch
A longer vibrating string has a lower fundamental frequency. Lower frequency is perceived as lower pitch. That is why longer strings on instruments are used for deeper notes.
In an open organ pipe, the displacement at both ends is typically?
Correct Answer: A. A node and an antinode
In an open pipe, air is free to move at both ends. This makes displacement antinodes at both open ends. Pressure nodes occur where displacement is maximum.
In a pipe closed at one end, the displacement pattern at the ends is typically?
Correct Answer: A. Node at closed end and antinode at open end
At the closed end, the air cannot move, so displacement is zero. At the open end, air can move freely, so displacement is maximum. This creates a node at the closed end and an antinode at the open end.
Standing waves are formed mainly by?
Correct Answer: B. Superposition of two identical waves traveling in opposite directions
Standing waves form when two waves of the same frequency move oppositely and overlap. The interference creates fixed nodes and antinodes in space. This pattern appears in strings and air columns during resonance.
In a standing wave, a node is a point where?
Correct Answer: A. Displacement is always zero
The correct answer is 'Displacement is always zero'. A node is a point that does not move in a standing wave. It occurs due to постоян destructive interference at that location. The distance between consecutive nodes is half a wavelength.
Resonance in musical instruments is useful because it?
Correct Answer: D. Stops energy transfer from source
The correct answer is 'Stops energy transfer from source'. Resonance allows a system to respond strongly at certain frequencies. This increases the vibration amplitude and makes the sound louder. Sound boxes and air columns use resonance to enhance musical tones.
Sound in liquids and gases cannot be polarized mainly because it is?
Correct Answer: A. Always reflected fully
The correct answer is 'Always reflected fully'. Polarization is a property of transverse waves. In fluids, sound is primarily longitudinal with particle motion along the direction of travel. Therefore sound in liquids and gases cannot be polarized.
When a sound wave enters a different medium, which quantity usually remains unchanged?
Correct Answer: A. Frequency
The frequency is fixed by the source and usually does not change at a boundary. Speed depends on the medium, so it can change after entering a new medium. Wavelength then adjusts because v equals f times wavelength.
If the speed of sound increases while frequency stays the same, the wavelength will?
Correct Answer: A. Increase
Wavelength equals speed divided by frequency for a given wave. If frequency is constant and speed increases, the wavelength must increase. This is why sound has different wavelengths in different media.