A radioactive source has a half-life of 80 s. How long it will take to decay 7/8th of the source?
Correct answer: C. 240 sec
- A. 10 sec
- B. 70 sec
- C. 240 sec
- D. 640 sec
Explanation
With each half-life, half the sample decays, ⅞ of the sample is the same as three half-lives. As the sample goes from 1 to ½ to ¼ to ⅛, halving each time, so 3x80= 240s
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