badge image

Enroll For Free Now & Improve Your Performance.

User Icon
User Icon
User Icon
User Icon
User Icon

Thank you for registering.

One of our academic counsellors will contact you within 1 working day.

Please check your email for login details.

Use Coupon: CART20 and get 20% off on all online Study Material

Total Price: Rs.

There are no items in this cart.
Continue Shopping
Grade: 12


2 sample of diferent element (half lives t1 & t2) have same no. of nuclei at t=0. The time after which the activity are same is ? (ans:-{t1t2/0.693(t2-t1)}*ln[t2/t1]).

10 years ago

Answers : (2)

vikas askiitian expert
509 Points

let two be samples be X & Y & their half lives  t1 , t2 respectively...

activity(A) = N(lamda)                       (N is number of nuclie at any time)

(lamda is disintegration constant)

N = Noe-(lamda)t        .............1            (number of nuclie at any time)

No is the number of nuclie at t=0 .

activity of X after time t, initially both are having same number of nuclie...

 Ax = Noe-(lamda)xt(lamda)x   ....................2

 activity of Y after time t

 Ay = Noe-(lamda)yt (lamda)y .......................3

since both are having same activity so equating 2 & 3

 (lamda)x/(lamda)y = e t((lamda)x e-t(lamda)y

now using lamda = 0.693/t1/2 

 taking log both sides

  ln[t2/t1] = 0.693(1/t1 - 1/t2)t

 t =(t2t1)ln[t2/t1] / [0.693(t2-t1)]



10 years ago
Chetan Mandayam Nayakar
312 Points

Dear Rajan,

let k1 and k2 be the two decay constants.

k1=(ln2)/t1,and k2=(ln2)/t2, Let number of nuclei at t=0 be N

Activity at time 't'= kNe-kt

((ln2)/t1)Ne-(ln2)(t/t1)=((ln2)/t2)Ne-(ln2)(t/t2), solve for 't'

Please feel free to post as many doubts on our discussion forum as you can. If you find any question
Difficult to understand - post it here and we will get you the answer and detailed solution very quickly. We
are all IITians and here to help you in your IIT JEE preparation.

All the best Rajan !!!



Askiitians Experts


9 years ago
Think You Can Provide A Better Answer ?
Answer & Earn Cool Goodies

Course Features

  • 101 Video Lectures
  • Revision Notes
  • Previous Year Papers
  • Mind Map
  • Study Planner
  • NCERT Solutions
  • Discussion Forum
  • Test paper with Video Solution

Course Features

  • 110 Video Lectures
  • Revision Notes
  • Test paper with Video Solution
  • Mind Map
  • Study Planner
  • NCERT Solutions
  • Discussion Forum
  • Previous Year Exam Questions

Ask Experts

Have any Question? Ask Experts

Post Question

Answer ‘n’ Earn
Attractive Gift
To Win!!! Click Here for details