JEE Main 2021 · PhysicsNumerical answerNumerical valueEasyCalculation

JEE Main 25 July 2021, Shift 2, Physics Q27

Question 27 of 90 in this shift, Physics question 27 of 30, Section B.

The nuclear activity of a radioactive element becomes

\left(\frac{1}{8}\right)^{\text{th}}

of its initial value in 30 years. The half-life of radioactive element is __________ years.

Official answer

NTA final key.

Chapter: Nuclei
Topic: Radioactive Decay
Idea tested: Integer Half-Life Shortcuts

Same idea in other shifts

Asked 7× in all

27 Jul 2022, Shift 1 · Q48What is the half-life period of a radioactive material if its activity drops to 1/16 $^{th}$ of its initial value in 30 years?EasySingle correct
28 Jul 2022, Shift 1 · Q48The half life period of a radioactive substance is 60 days. The time taken for $\frac{7}{8}$ th of its original mass to disintegrate will…EasySingle correct
28 Jul 2022, Shift 1 · Q52A freshly prepared radioactive source of half life 2 hours 30 minutes emits radiation which is 64 times the permissible safe level. The…EasyNumerical value
28 Jul 2022, Shift 2 · Q18A radioactive sample decays $\frac{7}{8}$ times its original quantity in 15 minutes. The half-life of the sample isEasySingle correct
24 Jun 2022, Shift 2 · Q56A sample contains $10^{-2}$ kg each of two substances A and B with half lives 4 s and 8 s respectively. The ratio of their atomic weights…MediumNumerical value
25 Feb 2021, Shift 1 · Q19Two radioactive substances X and Y originally have $N_1$ and $N_2$ nuclei respectively. Half life of X is half of the half life of Y.…MediumSingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.