Question

The half-life of a radioactive substance is 30 minutes. the time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is

Answer 1

The half-life of a radioactive substance is 30 minutes. The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is

(1) 15 
(2) 30
(3) 40 
(4) 60

Answer 2

Answer:

The time taken is 60 minutes.

Explanation:

The given situation suggest the half-life of a radioactive substance which decays and time for time span in between two decay percentage is calculated as follows -

Given is that 40 % decay and 85 % decay with half-life as 30 min

As we know that, at 40 % decay, 60 % will be remaining

At 85 % decay, 15 percent will be remaining.

Remaining =  $\frac{15}{60}=\frac{1}{4}=\left(\frac{1}{2}\right)^{2}$

Thereby $(1 / 2)^{2}$ implies n = 2

$\begin{array}{l}{2=\mathrm{T} / \mathrm{t}_{1 / 2}} \\ {2=\mathrm{T} / 30} \\ {\mathrm{T}=2 \times 30} \\ \bold{{T=60 \text { minutes. }}}\end{array}$