Question
In a radioactive material the activity at time t1 is R1 and at a later time t2, it is R2. If the dacay constant of the material is λ, then
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R1 = R2 e-λ(t1 -t2 )
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R1 = R2 eλ(t1 -t2 )
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R1 = R2 e(t2 /t1 )
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R1 = R2
Solution
A.
R1 = R2 e-λ(t1 -t2 )
The decay rate R of radioactive materials the number of decays per second.
From radioactive decay law.
Thus, 
or 
...(i)
where 
is the activity of the radioactive material at time t = 0.
At time t1, 
...(ii)
At time t2, 
...(iii)
Dividing Eq. (ii) by (iii), we have,
