The activity of a radioactive material is 2.56 × 10-3 Ci. If the half life of the material is 5 days, after how many days the activity will become 2 × 10-5 Ci ?

Question

The activity of a radioactive material is 2.56 × 10-3 Ci. If the half life of the material is 5 days, after how many days the activity will become 2 × 10-5 Ci ? (A) 30 days (B) 35 days (C) 40 days (D) 25 days

Tardigrade Admin · Accepted Answer

( A / A 0)=( N / N 0) (2 × 10-5/2.56 × 10-3)=( N / N 0) ( N / N 0)=(1/128) ⇒ N =( N 0/128) After 7 half life activity comes down to given value T =7 × 5 =35 days

Q. The activity of a radioactive material is $2.56 \times 1 0^{- 3} C i$ . If the half life of the material is $5$ days, after how many days the activity will become $2 \times 1 0^{- 5} C i$ ?

30 days

35 days

40 days

25 days

$\frac{A}{A _{0}} = \frac{N}{N _{0}}$
$\frac{2 \times 1 0 ^{- 5}}{2.56 \times 1 0 ^{- 3}} = \frac{N}{N _{0}}$
$\frac{N}{N _{0}} = \frac{1}{128} \Rightarrow N = \frac{N _{0}}{128}$
After $7$ half life activity comes down to given value $T = 7 \times 5$
$= 35$ days

Q. The activity of a radioactive material is 2.56×10−3Ci. If the half life of the material is 5 days, after how many days the activity will become 2×10−5Ci ?