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Question: Answered & Verified by Expert
A radioactive element disintegrates at a rate proportional to the quantity of substance $\mathrm{Q}$ present at any time $\mathrm{t}$. What is the differential equation of the disintegration?
MathematicsDifferential EquationsNDANDA 2007 (Phase 2)
Options:
  • A $\frac{\mathrm{dQ}}{\mathrm{dt}}=-\mathrm{Q}$
  • B $\frac{\mathrm{dQ}}{\mathrm{dt}}=-\mathrm{kQ}, \mathrm{k} < 0$
  • C $\frac{d Q}{d t}=-k Q, k>0$
  • D $\frac{\mathrm{dQ}}{\mathrm{dt}}=\mathrm{Q} \quad$
Solution:
1328 Upvotes Verified Answer
The correct answer is: $\frac{d Q}{d t}=-k Q, k>0$
A radioactive element disintegrates at a rate proportional to the quantity of substance $Q$ present at any time $\mathrm{t}$.
$\Rightarrow \quad \frac{\mathrm{dQ}}{\mathrm{dt}} \propto-\mathrm{Q}$
$\Rightarrow \frac{\mathrm{dQ}}{\mathrm{dt}}=-\mathrm{kQ}, \mathrm{k}>0$ is a constant.
This is required differential equation.

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