If 10% of a radioactive material decays in 5 days, then the amount of the original material left after 20 days is approximately:

 

  • Option 1)

    60%

     

  • Option 2)

     65%

     

  • Option 3)

    70%

  • Option 4)

    75%

     

 

Answers (2)
V Vakul

As we learnt in concept

Number of nuclei after disintegration -

N=N_{0}e^{-\lambda t} or A=A_{0}e^{-\lambda t}

- wherein

Number of nucleor activity at a time is exponentional function

 

Initially \: N_1=0.90N_0 = N_0.e^{-\lambda t_1}

t_1= 5days

\Rightarrow e^{-5\lambda }=0.90 ............(1)

at \: t=t_2 =20 \:days

N=N_0.e^{-20\lambda }=N_0(e^{-5\lambda })^4

N=N_0.({0.90 })^4=0.65 N_0

\therefore 65 % original matter will left after 20 days.


Option 1)

60%

 

Incorrect

Option 2)

 65%

 

Correct

Option 3)

70%

Incorrect

Option 4)

75%

 

Incorrect

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