1
JEE Main 2021 (Online) 26th February Evening Shift
MCQ (Single Correct Answer)
+4
-1
The recoil speed of a hydrogen atom after it emits a photon in going from n = 5 state to n = 1 state will be :
A
4.34 m/s
B
2.19 m/s
C
3.25 m/s
D
4.17 m/s
2
JEE Main 2021 (Online) 26th February Morning Shift
MCQ (Single Correct Answer)
+4
-1
Given below are two statements : one is labeled as Assertion A and the other is labelled as Reason R.

Assertion A : An electron microscope can achieve better resolving power than an optical microscope.

Reason R : The de Broglie's wavelength of the electrons emitted from an electron gun is much less than wavelength of visible light.

In the light of the above statements, choose the correct answer from the options given below :
A
A is false but R is true.
B
Both A and R are true but R is NOT the correct explanation of A.
C
Both A and R are true and R is the correct explanation of A.
D
A is true but R is false.
3
JEE Main 2021 (Online) 25th February Evening Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
An electron of mass me and a proton of mass mp = 1836 me are moving with the same speed. The ratio of their de Broglie wavelength $${{{}^\lambda electron} \over {{}^\lambda proton}}$$ will be :
A
1
B
1836
C
$${1 \over {1836}}$$
D
918
4
JEE Main 2021 (Online) 25th February Evening Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710 V. When the incident wavelength is changed to a new value, the stopping potential is 1.43 V. The new wavelength is :
A
400 nm
B
329 nm
C
309 nm
D
382 nm
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