Karnataka Board PUCPUC Science 2nd PUC Class 12

When Charcoal is Prepared from a Living Tree, It Shows a Disintegration Rate of 15.3 Disintegrations of 14c per Gram per Minute. a Sample from an Ancient Piece of Charcoal - Physics

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Sum

When charcoal is prepared from a living tree, it shows a disintegration rate of 15.3 disintegrations of 14C per gram per minute. A sample from an ancient piece of charcoal shows 14C activity to be 12.3 disintegrations per gram per minute. How old is this sample? Half-life of 14C is 5730 y.

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Solution

Given:
Initial activity of charcoal, A0 = 15.3 disintegrations per gram per minute
Half-life of charcoal, `T_"1/2"` = 5730 years
Final activity of charcoal after a few years, A = 12.3 disintegrations per gram per minute

Disintegration constant, `lambda = 0.693/T_"1/2" = 0.693/5370 "y"^-1`

Let the sample take a time of t years for the activity to reach 12.3 disintegrations per gram per minute.

Activity of the sample, `A = A_0e^(-lambdat)`

`A = A_0e^(-0.693/5730 xx t)`

⇒`"In" 12.3/15.3 = (-0.693)/5730 t`

⇒ `0.218253 = 0.693/5730 t`

⇒ t = 1804.3 years

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Chapter 24: The Nucleus - Exercises [Page 443]

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HC Verma Class 11, Class 12 Concepts of Physics Vol. 2
Chapter 24 The Nucleus
Exercises | Q 33 | Page 443

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