Acoustics and Sound Waves

Echolocation is a biological system where animals emit sound waves and interpret the echoes to navigate and find objects. Bats and dolphins are famous users of echolocation. Doppler effect describes frequency change, ultrasound is high-frequency sound used in imaging, and echomilekko is not a real term.

The loudest sound produced by any animal is NOT from the African Elephant. The sperm whale produces clicks that can reach 230 decibels. Even among terrestrial animals, the howler monkey or certain other species produce louder sounds than elephants. The claim is false.

Dog whistles produce ultrasonic sounds (above 20 kHz) which are beyond the range of human hearing but within dogs' hearing range. Dogs can hear frequencies up to about 45-65 kHz, much higher than humans. Infrasound (below 20 Hz) would not be useful for dog training as dogs also have limited sensitivity there.

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.

Tejas is India's indigenously developed lightweight multirole fighter aircraft under the Light Combat Aircraft (LCA) program. The other options are incorrect - it's not a mechanical wave, fuel device, or sound device.

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.