Q: How can excessive reverberation be reduced in halls?
A: By using sound-absorbent materials like compressed fibreboard, rough plaster, or draperies on walls and ceiling.
Q: What is sound and how is it produced?
A: Sound is a form of energy that produces a sensation of hearing. It is produced by vibrating objects.
Q: What is a medium in sound propagation?
A: A medium is the matter or substance through which sound is transmitted. It can be solid, liquid or gas.
Q: What is a compression in a sound wave?
A: A compression is a region of high pressure and density where particles of the medium are crowded together.
Q: What is wavelength in sound waves?
A: Wavelength is the distance between two consecutive compressions or two consecutive rarefactions in a sound wave.
Q: What type of wave is sound?
A: Sound is a longitudinal wave where particles move parallel to the direction of wave propagation.
Q: What is frequency in sound waves?
A: Frequency is the number of complete oscillations per unit time. Its SI unit is hertz (Hz).
Q: What determines the loudness of sound?
A: The amplitude (height) of the sound wave determines its loudness.
Q: What determines the pitch of sound?
A: The frequency of the sound wave determines its pitch – higher frequency means higher pitch.
Q: What is the audible range for humans?
A: The audible range for humans is approximately 20 Hz to 20,000 Hz.
Q: What is an echo?
A: An echo is the reflection of sound heard distinctly after the original sound.
Q: What is the minimum distance needed for an echo?
A: The minimum distance needed is 17.2 meters from the source to the reflecting surface.
Q: What is reverberation?
A: Reverberation is the persistence of sound due to repeated reflections from surfaces.
Q: What is infrasound?
A: Infrasound refers to sound waves with frequencies below 20 Hz.
Q: What is ultrasound?
A: Ultrasound refers to sound waves with frequencies above 20,000 Hz.
Q: How does temperature affect sound speed?
A: Speed of sound increases with increase in temperature of the medium.
Q: In which medium does sound travel fastest?
A: Among common materials, sound travels fastest in solids, followed by liquids, and then gases.
Q: What is a stethoscope based on?
A: A stethoscope works on the principle of multiple reflection of sound.
Q: Why are concert hall ceilings curved?
A: Ceilings are curved to reflect sound uniformly to all parts of the hall.
Q: What is the time lag needed to hear a distinct echo?
A: A minimum time interval of 0.1 seconds is needed to hear a distinct echo.
Q: What is the relation between speed, wavelength and frequency of sound?
A: Speed = wavelength × frequency (v = λν)
Class 9 Work and Energy Extra Question Answer
