What is the minimum distance required to hear a distinct echo? (Assuming speed of sound in air is 344 m/s)
A. 17.2 meters
B. 34.4 meters
C. 10 meters
D. 25.6 meters
Answer: Option A
Solution (By JKExamLibrary)
The human ear retains the sensation of sound for about 0.1 seconds (persistence of hearing). To hear a distinct echo, the reflected sound must reach the ear after at least 0.1 s. Distance traveled by sound = Speed × Time = 344 m/s × 0.1 s = 34.4 m. Since this is the total distance (go and return), the minimum distance to the obstacle is 34.4 / 2 = 17.2 meters.
Explanation:
The eye lens is a convex (converging) lens. It converges light rays to form a real and inverted image on the retina. The brain processes this signal and flips it so we perceive the world as erect. All other statements are functionally correct. The cornea does indeed do about two-thirds of the focusing.
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