JEE Main 2017 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 2 April 2017 (offline), Physics Q26

Question 26 of 90 in this shift, Physics question 26 of 30.

A radioactive nucleus A with a half life T, decays into a nucleus B. At

t=0

, there is no nucleus B. At sometime t, the ratio of the number of B to that of A is 0.3. Then, t is given by :

(1) $t=\frac{T}{2}\frac{\log 2}{\log 1.3}$
(2) $t=T\frac{\log 1.3}{\log 2}$ Official answer
(3) $t=T\log(1.3)$
(4) $t=\frac{T}{\log(1.3)}$

Official answer

Option 2

CBSE answer key (25/04/2017, used for result).

Chapter: Nuclei
Topic: Radioactive Decay
Idea tested: Statistical Decay Law

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Asked 5× in all

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Question text from the official JEE Main paper published by NTA (CBSE ran the 2017 exam); 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.