NTA Abhyas JEE Main2020PhysicsNuclear PhysicsPractice
Nucleus A decays into B with a decay constant λ 1 and B further decays into C with a decay constant λ 2 . Initially, at t = 0 , the number of nuclei of A and B were 3 N 0 and N 0 respectively. If at t = t 0 number of nuclei of B becomes constant and equal to 2 N 0 , then
Options
- At 0 = 1 λ 1 ln 3 λ 1 2 λ 2
- Bt 0 = 1 λ 1 ln λ 1 λ 2
- Ct 0 = 1 λ 1 ln 2 λ 1 3 λ 2
- Dt 0 = 1 λ 2 ln 3 λ 1 2 λ 2
Correct answer
A. t 0 = 1 λ 1 ln 3 λ 1 2 λ 2
Step-by-step solution
N A = 3 N 0 e – λ 1 t d N A d t = - 3 λ 1 N 0 e - λ 1 t d N B d t = 3 λ 1 N 0 e - λ 1 t - λ 2 N B At t = t 0 , d N B d t = 0 ⇒ 3 λ 1 N 0 e - λ 1 t - λ 2 N B = 0 ⇒ 3 λ 1 N 0 e - λ 1 t = λ 2 2 N 0 e λ 1 t 0 = 3 λ 1 2 λ 2 ⇒ t 0 = 1 λ 1 ln 3 λ 1 2 λ 2