Acoustics and Sound Waves

Sound travels fastest in solids because particles are closely packed, allowing faster transmission of vibrations. Speed of sound decreases from solids (~6000 m/s in steel) to liquids (~1500 m/s in water) to gases (~343 m/s in air). Sound cannot travel in vacuum.

Echoes are produced when sound waves reflect off a hard surface and return to the listener after a delay. The sound must travel a minimum distance to create a perceptible echo. Refraction, polarisation, and diffraction are other wave phenomena but do not cause echoes.

The shell resonates ambient sound from the environment, primarily blood flow and other internal noises. This creates the ocean-like effect. It's not actual ocean sound but resonance of the ear cavity itself.

Fever FM is an Indian FM radio station that operates at 104.0 MHz in several major cities including Delhi. This frequency is part of the higher end of the FM band and is consistently used by Fever FM. The other options include frequencies for Radio Mirchi (98.3) and Meow (104.8).

Meow 104.8 FM is an Indian radio station that broadcasts at 104.8 MHz, primarily in the Delhi region. The station's name directly references its frequency, making it easy to remember. The other options include frequencies for Fever FM (104.0) and FM Rainbow (102.6).

Sound travels approximately 1,500 meters per second in water compared to about 340 meters per second in air. The ratio is roughly 4.4:1, so '4 times faster' is the closest approximation among the options. This difference occurs because water is denser and less compressible than air, allowing sound waves to propagate more efficiently.

The pain threshold for human hearing is around 120-130 dB, which causes discomfort or pain in the ear. Normal conversation is 60-70 dB. Prolonged exposure above 85 dB can damage hearing. The "dba" appears to be a typo for "dB" but the numerical range is correct.

Sound is produced by the vibration of air molecules or any medium. These vibrations create pressure waves that our ears detect as sound. 'Photons of sound' is incorrect - photons are particles of light, not sound. Loudness is measured in decibels, not bels, making option C inaccurate.

Wavelength is defined as the distance between two consecutive crests or troughs of a wave. It represents the spatial period of the wave. Loudness is related to amplitude, frequency is the number of wave cycles per second, and amplitude is the maximum displacement from equilibrium.

Frequency is measured in both hertz and cycles per second - these are equivalent units. One hertz equals one cycle per second. This is a case where both naming conventions are valid and used interchangeably in physics.

Normal conversation typically measures around 60 decibels. 100 dB would be extremely loud (like a chainsaw or motorcycle), 50 dB is quieter than normal speech, and 80 dB is closer to heavy traffic or a noisy restaurant. The 60 dB range accurately represents typical human conversation levels.

Sounds with frequencies higher than 20,000 hertz are called ultrasonic. This is above the upper limit of human hearing. Infrasonic refers to sounds below 20 Hz, supersonic refers to objects moving faster than the speed of sound, and sonic boom is the shockwave created when an object breaks the sound barrier.

At sea level and 25°C, the speed of sound in air is approximately 346 meters per second. Among the given choices, 330 m/s is the closest standard approximation often used in physics problems for air at slightly cooler temperatures (0-20°C).

Sound actually travels FASTER in humid air because water vapor is less dense than dry air (the molecular weight of H₂O is 18 vs N₂=28, O₂=32). Lower density means faster sound propagation, making statement C the incorrect one.

Supersonic refers to speeds faster than the speed of sound (Mach 1, about 1235 km/h). 'Super' means above or beyond, so supersonic means beyond sound speed. Light speed is much faster, gravity is a force not a speed, and warp speed is science fiction.