1
JEE Main 2019 (Online) 9th January Evening Slot
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
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 :
A
4ln2
B
$${{\ln 2} \over 2}$$
C
$${{\ln 2} \over 4}$$
D
2ln2
2
JEE Main 2019 (Online) 9th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
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 :
A
5 days and 10 days
B
10 days and 40 days
C
20 days and 5 days
D
20 days and 10 days
3
JEE Main 2018 (Online) 16th April Morning Slot
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
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 :
A
20 years and 5 years, respectively
B
20 years and 10years, respectively
C
5 years and 20 years, respectively
D
10 years and 20 years, respectively
4
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Change Language
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 nth state and the ground state respectively. Let $${\Lambda _n}$$ be the wavelength of the emitted photon in the transition from the nth state to the ground state. For large n, (A, B are constants)
A
$${\Lambda _n} \approx A + {B \over {\lambda _n^2}}$$
B
$${\Lambda _n} \approx A + B{\lambda _n}$$
C
$$\Lambda _n^2 \approx A + B\lambda _n^2$$
D
$$\Lambda _n^2 \approx \lambda$$
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