Modern Physics - NEET Physics Questions
← All Chapters

Modern Physics

Question 21: moderate

Consider the following nuclear reactions and select the correct statements from the options that
follow.

(A) Free neutron has higher mass than proton, therefore reaction I is possible
(B) Free proton has less mass than neutron, therefore reaction II is not possible for the free
proton
(C) Inside a nucleus, both decays (reaction I and II) are possible
(D) Inside a nucleus, reaction I is not possible but reaction II is possible.

1. A, B, C are correct
2. A, C, D are correct
3. A, B, D are correct
4. B, C, D are correct
View Answer
Question 22: moderate

Mark the incorrect statement :

1. Following alpha or beta decay a nucleus reaches its ground state after emitting nuclear gamma rays.
2. A proton can not decay to a neutron in a nuclei because such decay has negative Q value of reaction.
3. A positron can capture electron resulting in gamma rays photon only.
4. In positive beta decay the emitted positron shows continuous distribution of kinetic energy.
View Answer
Question 23: moderate

The correct graph between the maximum energy of a photoelectron and the inverse of wavelength of the incident radiation is given by the curve

1. A
2. B
3. C
4. None of the above
View Answer
Question 24: difficult

A photon and an electron have equal energy E. \[\lambda_{photon}/\lambda_{electron}\] is proportional to

1. √E
2. 1/√E
3. 1/E
4. Does not depend upon E
View Answer
Question 25: difficult

Ultraviolet light of wavelength 300 nm and intensity 1.0 watt/m² falls on the surface of a photosensitive material. If 1% of the incident photons produce photoelectrons, then the number of photoelectrons emitted from an area of 1.0 cm² of the surface is nearly

1. \[9.61\times 10^{14}per sec\]
2. \[4.12\times 10^{13}per sec\]
3. \[1.51\times 10^{12}per sec\]
4. \[2.13\times 10^{11}per sec\]
View Answer
Question 26: moderate

A photon of wavelength 6630 Å is incident on a totally reflecting surface. The momentum delivered by the photon is equal to

1. \[6.63\times 10^{-27}kg-m/sec\]
2. \[2\times 10^{-27}kg-m/sec\]
3. \[10^{-27}kg-m/sec\]
4. \[3\times 10^{-27}kg-m/sec\]
View Answer
Question 27: difficult

Photoelectric emission is observed from a metallic surface for frequencies ν1 and ν2 of the incident light rays (ν1 > ν2). If the maximum value of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of 1 : k, then the threshold frequency of the metallic surface is :

1. \[\frac{\nu_{1}-\nu_{2}}{k-1}\]
2. \[\frac{k\nu_{1}-\nu_{2}}{k-1}\]
3. \[\frac{k\nu_{2}-\nu_{1}}{k-1}\]
4. \[\frac{\nu_{2}-\nu_{1}}{k}\]
View Answer
Question 28: moderate

The ratio of de-Broglie wavelengths of molecules of hydrogen and helium which are at temperature 27°C and 127° respectively is :

1. 1/2
2. \[\sqrt{\frac{3}{8}}\]
3. \[\sqrt{\frac{8}{3}}\]
4. 1
View Answer
Question 29: moderate

What is energy released in the β-decay of \[^{32}P\longrightarrow ^{32}S\] ?

\[\left( Given:atomic masses:-31.97391amu for ^{32}P and 31.97207amu for ^{32}S \right)\]

1. –1.2 Mev
2. +1.7 Mev
3. +2.1 Mev
4. –0.9 Mev
View Answer
Question 30: difficult

The figure shows the variation of photo current with anode potential for a photo-sensitive surface for three different radiations. Let Ia, Ib, and Ic be the intensities and fa, fb and fc be the frequencies for the curves a, b and c respectively :

1. \[f_{a}=f_{b} and I_{a}\neq I_{b}\]
2. \[f_{a}=f_{c} and I_{a}= I_{c}\]
3. \[f_{a}=f_{b} and I_{a}= I_{b}\]
4. \[f_{b}=f_{c} and I_{b}= I_{c}\]
View Answer