1
JEE Main 2020 (Online) 7th January Evening Slot
MCQ (Single Correct Answer)
+4
-1
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 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
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 $$\mathop A\limits^o $$
3
JEE Main 2019 (Online) 12th April Morning Slot
MCQ (Single Correct Answer)
+4
-1
The stopping potential V0 (in volt) as a function of frequency ($$\upsilon $$) for a sodium emitter, is shown in the figure. The work function of sodium, from the data plotted in the figure, will be:
(Given: Planck’s constant (h) = 6.63 × 10–34 Js, electron charges e = 1.6 × 10–19 C) JEE Main 2019 (Online) 12th April Morning Slot Physics - Dual Nature of Radiation Question 99 English
A
1.95 eV
B
2.12 eV
C
1.82 eV
D
1.66 eV
4
JEE Main 2019 (Online) 10th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
A 2 mW laser operates at wavelength of 500 nm. The number of photons that will be emitted per second is : [Given Planck's constant h = 6.6 × 10–34 Js, speed of light c = 3.0 × 108 m/s]
A
5 × 1015
B
1.5 × 1016
C
1 × 1016
D
1 × 1016
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