Question

Half-life of a radioactive substance is 20 minutes. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately –

• A. 10 min
• B. 20 min
• C. 30 min
• D. 40 min

Answer 1

Answer: (B)

20 min

Answer 2

t₁ = 3.32 × 20 × log₁₀ $\left( \frac { 100 } { 67 } \right)$

t₂ = 3.32 × 20 × log₁₀ $\left( \frac { 100 } { 33 } \right)$

Dt = t₂ – t₁ = 20 min