Half life of a radioactive substance is T. The time taken for all the nuclei to disintegrate will be
(a) 2T           (b) T2
(c) 4T           (d) Uncertain

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Radioactivity
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The half life of polonium is 140 days. After how many days, 16 gm polonium will be reduced to 1 gm (or 15g will decay) 
(a) 700 days            (b) 280 days
(c) 560 days            (d) 420 days

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Radioactivity
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A radioactive element emits 200 particles per second. After three hours 25 particles per second are emitted. The half life period of element will be
(a) 50 minutes            (b) 60 minutes
(c) 70 minutes            (d) 80 minutes

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The half life of the isotope Na1124 is 15 hrs. How much time does it take for 78th of a sample of this isotope to decay

(a) 75 hrs               (b) 65 hrs
(c) 55 hrs               (d) 45 hrs

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If the half life of a radioactive sample is 10 hours,
its mean life is 
(a) 14.4 hours               (b) 7.2 hours
(c) 20 hours                  (d) 6.93 hours

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Radioactivity
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If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in 4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm 
(a) In 8 minutes              (b) In 12 minutes
(c) In 16 minutes             (d) In 20 minutes

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16 gm sample of a radioactive element is taken from Bombay to Delhi in 2 hour and it was found that 1 gm of the element remained (undisintegrated). Half life of the element is 
(a) 2 hour           (b) 1 hour
(c) 12 hour         (d) 14hour

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Radioactivity
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Unit of radioactivity is Rutherford. Its value is

(a) 3.7×1010 disintegrations/sec
(b) 3.7×106 disintegrations/sec
(c) 1.0×1010disintegrations/sec
(d) 1.0×106 disintegrations/sec

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Radioactivity
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A radioactive substance has a half life of 60 minutes. After 3 hours, the fraction of atom that have decayed would be

(a) 12.5%               (b) 87.5%
(c) 8.5%                 (d) 25.1%

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An element used for radioactive carbon dating for more than 5600 years is 
(a) C-14          (b) U-234
(c) U-238        (d) Po-94

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Radioactivity
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