Acoustics and Sound Waves

The speed of sound in air at 25°C is approximately 346 m/s. Among the options, 330 m/s is the closest approximation. The speed of sound in air increases with temperature and is roughly 331 m/s at 0°C, increasing by about 0.6 m/s per degree Celsius.

The Mach number represents the ratio of an object's speed to the speed of sound in the surrounding medium. It is primarily used to characterize aircraft velocities, classifying flight regimes from subsonic (M<1) to supersonic (M>1).

The decibel (dB) is the standard unit for measuring sound intensity and amplitude. Coulomb measures electric charge. 'Hum' is not a standard unit. 'Cycles' refers to frequency (Hz), not amplitude. Sound amplitude determines loudness and is measured logarithmically in decibels.

The decibel (dB) measures the intensity or loudness of sound. Speed of light is measured in m/s. Radio wave frequency is measured in Hertz. Heat intensity can be measured in temperature units or calories/watts, not decibels. Decibels can also measure other logarithmic ratios (like signal power), but sound intensity is the most common educational context.

A fathom is a unit of depth measurement used primarily in nautical contexts to measure water depth (1 fathom = 6 feet). While it technically measures distance, in educational contexts it's specifically associated with depth. Sound uses decibels. Frequency uses Hertz. General distance uses meters or feet.

Sound waves in air are longitudinal waves - the particles oscillate parallel to the direction of wave propagation (compression and rarefaction). Only transverse waves can be polarized. Sound is NOT electromagnetic.

High Frequency (HF) RFID operates at 13.56 MHz, which is the international standard for HF RFID systems (ISO/IEC 14443, ISO/IEC 15693). Low Frequency (LF) uses 125 kHz, Ultra High Frequency (UHF) uses 915 MHz, and microwave uses 2.54 GHz.

DTMF stands for Dual Tone Multi-Frequency, the signaling system used in telephones where each key press generates two specific tones simultaneously. This enables reliable digit recognition over telephone networks.

High Frequency (HF) band is the ITU designation for 3 to 30 MHz radio frequencies. This band is used for shortwave radio broadcasting, amateur radio, and various communications services. The other options are incorrect: 100 kHz would be in the LF band, 1 GHz is in the UHF band, and 30-300 MHz is the VHF band.

Hearing aids amplify sound waves to help overcome conductive hearing loss, which occurs when sound cannot efficiently pass through the outer and middle ear. In nerve (sensorineural) deafness, the damage is to the inner ear or auditory nerve itself, so amplifying sound cannot help because the neural pathway for transmitting sound signals to the brain is impaired.

Yes, this is the correct answer. Sound needs medium to travel, which is not present in vacuum.

Decibel (dB) is a unit that is used to measure intensity of sound level.

Sound travels through the ear in this sequence: outer ear collects sound waves, ear canal directs them to the eardrum, eardrum vibrations are transmitted through the middle ear to the inner ear, and finally the inner ear converts vibrations to electrical signals for the brain. Option D correctly lists this order.

Sound cannot travel through vacuum.