Department of Pre-University Education, Karnataka course PUC Karnataka Science Class 12
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# 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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ConceptRadioactivity Law of Radioactive Decay

#### Question

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.

#### 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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Solution 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 Concept: Radioactivity - Law of Radioactive Decay.
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