1
JEE Main 2020 (Online) 7th January Evening Slot
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
The activity of a radioactive sample falls from 700 s–1 to 500 s–1 in 30 minutes. Its half life is close to:
A
62 min
B
66 min
C
72 min
D
52 min
2
JEE Main 2020 (Online) 7th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
The time period of revolution of electron in its ground state orbit in a hydrogen atom is 1.6 $$ \times $$ 10-16 s. The frequency of revolution of the electron in its first excited state (in s-1) is :
A
5.6 $$ \times $$ 1012
B
1.6 $$ \times $$ 1014
C
7.8 $$ \times $$ 1014
D
6.2 $$ \times $$ 1015
3
JEE Main 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Consider an electron in a hydrogen atom revolving in its second excited state (having radius 4.65 $$\mathop A\limits^o $$). The de-Broglie wavelength of this electron is :
A
6.6 $$\mathop A\limits^o $$
B
3.5 $$\mathop A\limits^o $$
C
9.7 $$\mathop A\limits^o $$
D
12.9 $$\mathop A\limits^o $$
4
JEE Main 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
The electron in a hydrogen atom first jumps from the third excited state to the second excited state and subsequently to the first excited state. The ratio of the respective wavelengths, $${{{\lambda _1}} \over {{\lambda _2}}}$$, of the photons emitted in this process is :
A
$${{22} \over 5}$$
B
$${7 \over 5}$$
C
$${9 \over 7}$$
D
$${{20} \over 7}$$
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