A radioactive sample has a half-life of 5 years. What fraction of the original active nuclei will remain undecayed after 15 years? MCQ with Answer and Explanation
A radioactive sample has a half-life of 5 years. What fraction of the original active nuclei will remain undecayed after 15 years?
A. 1/8
B. 1/3
C. 1/15
D. 1/2
Answer: Option A
Solution (By JKSSB Mock Tests)
The number of half-lives (n) that have passed is total time / half-life = 15 / 5 = 3 half-lives. The fraction of the sample remaining undecayed is given strictly by the formula (1/2)^n. Therefore, the fraction remaining is (1/2)^3 = 1/2 * 1/2 * 1/2 = 1/8.
Explanation:
Myopia (nearsightedness): image formed before retina, corrected with concave lens. Hypermetropia: cannot see near objects. Presbyopia age-related. Cataract lens opacity.
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