JEE Main 2019 (Online) 9th January Morning Slot | Atoms and Nuclei Question 141 | Physics

JEE Main 2019 (Online) 9th January Morning Slot

MCQ (Single Correct Answer)

-1

A sample of radioactive material A, that has an activity of 10 mCi(1 Ci = 3.7 $$ \times $$ 10¹⁰ decays/s), has twice the number of nuclei as another sample of a different radioactive materail B which has an activity of 20 mCi. The correct choices for half-lives of A and B would then be respectively :

5 days and 10 days

10 days and 40 days

20 days and 5 days

20 days and 10 days

JEE Main 2018 (Online) 16th April Morning Slot

MCQ (Single Correct Answer)

-1

Both the nucleus and the atom of some element arein their respective first excited states. They get de-excted by emitting photons of wavelengths ^{$$\lambda $$}N, ^{$$\lambda $$}A respectively. The ratio $${{{}^\lambda N} \over {{}^\lambda A}}$$is closest to :

10^$$-$$6

10^$$-$$10

10^$$-$$1

JEE Main 2018 (Online) 16th April Morning Slot

MCQ (Single Correct Answer)

-1

At some instant, a radioactive sample S₁ having an activity 5 $$\mu $$Ci has twice the number of nuclei as another sample S₂ which has an activity of 10 $$\mu $$Ci. The half lives of S₁ and S₂ are :

20 years and 5 years, respectively

20 years and 10years, respectively

5 years and 20 years, respectively

10 years and 20 years, respectively

JEE Main 2018 (Offline)

MCQ (Single Correct Answer)

-1

An electron from various excited states of hydrogen atom emit radiation to come to the ground state. Let $${\lambda _n}$$, $${\lambda _g}$$ be the de Broglie wavelength of the electron in the n^th state and the ground state respectively. Let $${\Lambda _n}$$ be the wavelength of the emitted photon in the transition from the n^th state to the ground state. For large n, (A, B are constants)

$${\Lambda _n} \approx A + {B \over {\lambda _n^2}}$$

$${\Lambda _n} \approx A + B{\lambda _n}$$

$$\Lambda _n^2 \approx A + B\lambda _n^2$$

$$\Lambda _n^2 \approx \lambda$$

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