Question

Find the number of Half-Life elapsed before which 93.5 75% of a radioactive sample has decayed

Answer 1

four half lifes elapsed before which 93.75% of the radioactive sample has decayed.

we have to find the number of half life elapsed before which 93.75 % of a radioactive sample has decayed.

half life is the time taken to decay half amount of radioactive substance.

let N is initial amount of radioactive substance.

remaining amount of radioactive substance = N - 93.75% of N = 6.25%

during 1st half life period ⇒N/2 ( 50% )

during 2nd half life period ⇒N/4 ( 25% )

during 3rd half life period ⇒N/8 ( 12.5 % )

during 4th half life period ⇒N/16 (6.25 %)

here it is clear that after 4th half life, 6.25% of radioactive substance remains undecayed.

therefore four half lifes elapsed before which 93.75% of the radioactive sample has decayed.