The phenomenon of total internal reflection occurs when light travels from: MCQ with Answer and Explanation
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A bullet of mass 10 g moving at 300 m/s penetrates 10 cm into a wooden block. Average resistive force is
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The unit of luminous flux is
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The half-life of a radioactive substance is 10 days. After 30 days, the fraction remaining undecayed is:
Correct Answer: Option D
Explanation:
Number of half-lives n = total time / half-life = 30 days / 10 days = 3. Fraction remaining = (1/2)ⁿ = (1/2)³ = 1/8. This exponential decay law is fundamental in radioactivity. Memory tip: 'After n half-lives, fraction = 1/2ⁿ'. Competitive exams frequently test such calculations with varying time intervals. Always compute number of half-lives first. Note: Activity (decays per second) also reduces by same fraction. This problem assesses understanding of half-life concept beyond rote memorization.
Number of half-lives n = total time / half-life = 30 days / 10 days = 3. Fraction remaining = (1/2)ⁿ = (1/2)³ = 1/8. This exponential decay law is fundamental in radioactivity. Memory tip: 'After n half-lives, fraction = 1/2ⁿ'. Competitive exams frequently test such calculations with varying time intervals. Always compute number of half-lives first. Note: Activity (decays per second) also reduces by same fraction. This problem assesses understanding of half-life concept beyond rote memorization.
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