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UPSC Prelims 1992 · Environment · Species Watch
The bats are able to fly in dark since their wings produce
- (a) Infrared rays
- (b) Ultrasonic waves
- (c) Sound waves
- (d) Ultraviolet rays
Show the answer and explanation
Answer: (b) Ultrasonic waves
Bats make ultrasonic calls (too high for us to hear) and listen to the echoes — echolocation.
The idea
A bat “sees” with sound. It sends out very high-pitched calls and listens for the echo. From the time the echo takes and the way it changes, the bat knows where an object is, how big it is and how it is moving.
Bat gives out an ultrasonic call → Sound hits an insect or a wall → Echo returns to the bat’s ears → Brain builds a sound picture → Bat turns or catches the insect
Why the others are wrong
(c) Ultrasound is sound, but “ultrasonic” is the precise answer.
The trap
Ultrasound is a kind of sound, so (c) is not absurd. UPSC wants the precise term. (Bats make these calls with the larynx, not the wings.)
Also know
Ultrasound is sound above about 20,000 hertz, beyond human hearing. Dolphins and toothed whales use the same method under water. Ships’ sonar copies it.
🔒 Echolocation: bats, dolphins — ultrasonic sound + echo.