Acoustics and Sound Waves

Ultrasonic sound is defined as sound waves with frequencies above 20 kHz (20,000 Hz), which is the upper limit of human hearing. The human audible range is 20 Hz to 20 kHz, so anything above 20 kHz is ultrasonic. Ultrasound is used in medical imaging, cleaning, and various industrial applications.

Infrasonic sound refers to sound waves with frequencies below 20 Hz, which is below the lower limit of human hearing. While humans cannot hear infrasound, it can still be felt as vibrations or pressure changes. Some animals like elephants and whales can use infrasound for communication over long distances.

RADAR (Radio Detection and Ranging) uses electromagnetic waves (radio waves) to detect objects, while SONAR (Sound Navigation and Ranging) uses sound waves for underwater detection. The order in option B is RADAR first, then SONAR - electromagnetic wave for RADAR and sound wave for SONAR. This order matches the question sequence.

The cracking sound from knuckles is indeed caused by gas bubbles in the synovial fluid collapsing. When you pull or bend your finger, you create negative pressure that causes dissolved gases (mostly nitrogen and carbon dioxide) to form bubbles. When these bubbles burst, they create the characteristic cracking sound. It takes about 20 minutes for the gas to redissolve, which is why you can't crack the same knuckle repeatedly.

The African elephant is not the loudest animal. The sperm whale produces clicks reaching 230 dB, making it the loudest animal. The pistol shrimp creates cavitation bubbles at 218 dB. Among terrestrial animals, the howler monkey and elephant are loud, but not at 188 dB specifically for elephants.

The study of fingerprints is called Dermatoglyphics, not Acoustics. Acoustics is the study of sound. Therefore the statement is false and option B is correctly marked.

Sound waves are mechanical waves that require particles to vibrate, so they need a material medium (solid, liquid, or gas) to travel. Light, microwaves, and radio waves are electromagnetic waves that can propagate through vacuum as they do not require any medium.

Cats can hear ultrasonic frequencies up to approximately 64,000 Hz, far beyond the human range of about 20,000 Hz. This ability helps them detect prey movements and communicate with kittens.

Decibels use a logarithmic scale, so adding sound sources doesn't add decibel values linearly. Two identical 90 dB sources combine to approximately 93 dB, not 180 dB.

The decibel (dB) scale measures sound intensity on a logarithmic scale, comparing a given sound pressure level to a reference value. It is used to quantify the loudness of sounds, with 0 dB representing the threshold of human hearing and normal conversation around 60 dB. The logarithmic nature means every 10 dB increase represents a tenfold increase in sound intensity.

The Hum is an unexplained low-frequency phenomenon reported in various locations worldwide. The Taos Hum (New Mexico, USA) is the most famous case, first widely reported in the early 1990s. Similar hums have been documented in the UK (Bristol Hum) and other places. The phenomenon is known as 'The Hum' or by location names (Taos Hum, Bristol Hum), not 'Tao's Hum'.

When you speak, you hear your voice through two pathways: air conduction (sound waves through air) and bone conduction (vibrations through skull bones). Bone conduction enhances lower frequencies, making your voice sound fuller to yourself. A recording only captures the air-conducted sound, which lacks this bass boost and thus sounds thinner and higher-pitched.

Light travels at approximately 300,000 kilometers per second, while sound travels at only 343 meters per second in air. This means light is nearly one million times faster than sound. When you're far from the action, the light arrives almost instantly, but the sound takes noticeable time to travel the same distance.

This is actually a myth - duck quacks DO echo. However, for this trivia question based on common misconception, C is the expected answer per the claim.