Physics 2012 JAMB Past Questions - Question 47: A piece of radio active material contains 1000 atoms .If its half life is 20 seconds ,the time taken for 125 atoms to remain is

Correct Answer

C

Explanation

To determine the time taken for 125 atoms to remain, we can use the concept of half-life.

The half-life of a radioactive material is the time it takes for half of the atoms to decay. In this case, the half-life is 20 seconds.

Since the initial number of atoms is 1000, we can calculate the number of half-lives it takes for the number of atoms to reduce to 125.

Number of half-lives = log(base 2) (initial number of atoms / final number of atoms)

Number of half-lives = log(base 2) (1000 / 125)

Number of half-lives = log(base 2) 8

Number of half-lives = 3

Therefore, it takes 3 half-lives for the number of atoms to reduce from 1000 to 125.

Since each half-life is 20 seconds, the total time taken would be:

Total time = Number of half-lives * Half-life

Total time = 3 * 20 seconds

Total time = 60 seconds

So, the time taken for 125 atoms to remain is 60 seconds.