KVPY SX SB Exam 2018 Question Paper

Question : 36 of 120

Marks: +1, -0

The graph shows the log of activity (log R) of a radioactive material as a function of time t in minutes.

The half-life (in minutes) for the decay is closest to

Solution:

R = λN_0 e^{–λt}

lnR = ln

(λN_0) (e^{– λt})

lnR =

-λt + \ln (λN_0)

comparing y = – mx + C
m = λ
By graph

M ={8-6}/{16-8}=1/4=λ

T_{1\/2}={\ln/λ}=0.693/{1\/4}=0.277

Closest value in 3.0.

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