Question

2. What are the units of half life? How many half lives have expired when a radioactive object decays

to 12.5% of its original radioactivity?

Answer 1

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Answer:

As we know half life is the time required for any quantity to reduce their 50 % of its initial value. The units of half life is Time.

To calculate the half life we use this formula-

N(t) =N(0) (1/2)ⁿ

Suppose initial quantity is 100, after a radioactive objective decay the value become 12.5 % of initial

N₀ = 100

N_t = 12.5

12.5 = 100 (1/2)ⁿ

12.5/100 = (1/2)ⁿ

(1/8) = (1/2)ⁿ

(1/2)³= (1/2)ⁿ

On comparing this n =3

Three half lives have expired to decay 12.5 % from its orignal radioactivity.