Echo minimum distance for distinct hearing (speed sound = 340 m/s, persistence = 0.1 s): MCQ with Answer and Explanation

Echo minimum distance for distinct hearing (speed sound = 340 m/s, persistence = 0.1 s):
A. 34 m
B. 8.5 m
C. 68 m
D. 17 m
Answer: Option D
Solution (By JKSSB Mock Tests)
Time for to-and-fro: t = 2d/v ≥ 0.1 s ⇒ d ≥ vt/2 = 340×0.1/2 = 17 m. Minimum distance for brain to distinguish echo from original sound. Memory tip: 'd_min = v×persistence/2'. Application of sound reflection with human perception limit, common in competitive exam numericals.

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The work done in moving a charge of 2 C between two points with potential difference of 12 V is:
A. 24 J
B. 6 J
C. 14 J
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Correct Answer: Option A


Explanation:
Work done W = charge (Q) × potential difference (V). Thus W = 2 C × 12 V = 24 J. This follows from definition of voltage: 1 volt = 1 joule per coulomb. The work done equals the change in electrical potential energy. This fundamental relationship is crucial in electricity. Memory tip: W = QV is analogous to mechanical work = force × distance. Such direct formula applications are common in competitive exams to test basic concept retention. Always verify units: coulomb × volt = joule, confirming dimensional consistency.

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Correct Answer: Option D


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Correct Answer: Option A


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