1.

The analysis of a uranium reveals that ratio of mole of .^(206)Pband .^(238) U in sample is 0.2 . If effective decay constant of process .^(238)U rarr .^(206) Pb is lambda then age of rock is

Answer»

`(1)/(lambda) In (5)/(4)`
`(1)/(lambda) In ((5)/(1))`
`(1)/(lambda) ln(4)/(1)`
`(1)/(lambda) In ((6)/(5))`

Solution :`t=(1)/(lambda)In[(n_(PB+n_(U))/(n_(U)))] ""...(i)`
GIVEN `(n_(Pb))/(n_(U))=0.2=(1)/(5) rArr (n_(Pb+n_(U))/(n_(U)))=(1)/(5)+1=((6)/(5))"" ...(II)`
SUBSTITUTING (ii)in(i)
`t=(1)/(lambda) In ((6)/(5))`


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