Photoelectric EffectHard
Question
Two isotopes P and Q of atomic weight 10 and 20, respectively are mixed in equal amount by weight. After 20 days their weight ratio is found to be 1 : 4. Isotope P has a half-life of 10 days. The half-life of isotope Q is
Options
A.zero
B.5 days
C.20 days
D.inifinite
Solution
No. of nucleus of P, NP = 
× NA
No. of nucleus of Q, NQ =
No. of Isotope P after 20 days, NP′ =
Let no. of Isotope Q after 20 days be NQ′
∴
(given)
NQ′ = 2 × NP′ =
= NQ
Thus no change in number of Q. Hence its half life is infinity.
× NANo. of nucleus of Q, NQ =
No. of Isotope P after 20 days, NP′ =
Let no. of Isotope Q after 20 days be NQ′
∴
(given)NQ′ = 2 × NP′ =
= NQThus no change in number of Q. Hence its half life is infinity.
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