The half-life of a certain radioactive substance is 12 hours. there are 19 grams present initially. a. express the amount of substance remaining as a function of time t. b. when will there be 8 grams remaining?

(a)

(b) 15 hours

Explanation:

half life, T = 12 hours

No = 19 g

(a) Let N be the amount remaining after time t.

Let λ be the decay constant.

The equation of radioactivity used here is given by

(b) N = 8 gram

Substitute the values in above equation

λ = 0.0577 per hour

So,

Take natural log on both the sides

- 0.0577 t = - 0.865

t = 15 hours

b) phosphorus pentoxide