JEE Main 2017 (Offline) | Atoms and Nuclei Question 206 | Physics

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 :

$$t = {T \over {\log (1.3)}}$$

$$t = T\log (1.3)$$

$$t = {T \over 2}{{\log 2} \over {\log 1.3}}$$

$$t = T{{\log 1.3} \over {\log 2}}$$

JEE Main 2016 (Online) 9th April Morning Slot

MCQ (Single Correct Answer)

-1

A hydrogen atom makes a transition from n = 2 to n = 1 and emits a photon. This photon strikes a doubly ionized lithium atom (z = 3) in excited state and completely removes the orbiting electron. The least quantum number for the excited state of the ion for the process is :

JEE Main 2016 (Offline)

MCQ (Single Correct Answer)

-1

Out of Syllabus

Half-lives of two radioactive elements $$A$$ and $$B$$ are $$20$$ minutes and $$40$$ minutes, respectively. Initially, the samples have equal number of nuclei. After $$80$$ minutes, the ratio of decayed number of $$A$$ and $$B$$ nuclei will be:

$$1:4$$

$$5:4$$

$$1:16$$

$$4:1$$

JEE Main 2015 (Offline)

MCQ (Single Correct Answer)

-1

As an electron makes a transition from an excited state to the ground state of a hydrogen - like atom/ion :

kinetic energy decreases, potential energy increases but total energy remains same

kinetic energy and total energy decrease but potential energy increases

its kinetic energy increases but potential energy and total energy decrease

kinetic energy, potential energy and total energy decrease