Question

Calculate the time interval between 33% decay and 67% decay if half-life of a substance is 20 minutes.

पर्याय

• 20 minutes

• 40 minutes

• 60 minutes

• 13 minutes

Answer 1

20 minutes

Explanation:

Decay constant,

`lambda=0.693/"T"_(1//2) = 0.693/20=0.03465  "min"^-1`

Time of decay, `"t"=2.303/lambda"log""N"_0/"N"`

when 33% decay,

`t_1=2.303/0.03465"log"100/67=11.6  "min"`

And when 67% decay,

`t_2=2.303/0.03465"log"100/33=32  "min"`.

Hence time interval

Δt = t₂ - t₁ = 32 - 11.6 = 20.4 ≈ 20 min.