JEE Main 2019 (Online) 10th January Morning Slot | Atoms and Nuclei Question 139 | Physics

JEE Main 2019 (Online) 10th January Morning Slot

MCQ (Single Correct Answer)

-1

Using a nuclear counter the count rate of emitted particles from a radioactive source is measured. At t = 0 it was 1600 counts per second and t = 8 seconds it was 100 counts per second. The count rate observed, as counts per second, at t = 6 seconds is close to -

200

150

400

360

JEE Main 2019 (Online) 9th January Evening Slot

MCQ (Single Correct Answer)

-1

At a given instant, say t = 0, two radioactive substance A and B have equal activities. the ratio $${{{R_B}} \over {{R_A}}}$$ of their activities after time t itself decays with time t as e^$$-$$3t. If the half-life of A is ln², the half-life of B is :

4ln2

$${{\ln 2} \over 2}$$

$${{\ln 2} \over 4}$$

2ln2

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

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