NEET Physics Nuclei Questions Solved

Watch Physics > Nuclei Videos
play button

In a radioactive material the activity at time t1 is R1 and at a later time t2, it is R2. If the decay constant of the material is λ, then

(a) R1=R2e-λt1-t2                                    (b) R1=R2eλt1-t2

(c) R1=R2t2t1                                          (d) R1=R2

(a) The decay rate R of a radioactive material is the number of decays per seconds.

From radioactive decaylaw,


or    -dNdt=λN

i.e. Rate of reaction is directly proportional to the initial concentration of reactants.

Thus,     R=-dNdt     or   RN

or         R=λN   or R=λN0e-λt                     ...(i)

where R0=λN0 is the activity of the radioactive material at time t=0.

At time t1,           R1=R0 e-λt1                      ...(ii)

At time t2,             R2=R0 e-λt2                      ...(iii)

Dividing Eq. (ii) by Eq. (iii), we have 


or    R1=R2 e-λt1-t2

Difficulty Level:

  • 64%
  • 27%
  • 8%
  • 4%
Crack NEET with Online Course - Free Trial (Offer Valid Till September 21, 2019)