# Assertion Reason Physics Chapter 11 Dual Nature of Radiation and Matter

Questions of Assertion Reason of Physics Chapter 11 Dual Nature of Radiation and Matter CBSE Class 12 are very simple to understand as this chapter deals with Dual Nature of Radiation and Matter. To solve assertion reason type questions of Physics, a deeper understanding of concept about Electron Emission, Photoelectric Effect, Experimental Study of Photoelectric Effect, Photoelectric Effect and Wave Theory of Light, Einstein’s Photoelectric Equation: Energy Quantum of Radiation, Particle Nature of Light: The Photon and Wave Nature of Matter is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.

How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.

How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.

In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:

Assertion (A)Reason (R)MCQ Options (Fixed for all questions)
If TrueTrue(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
If TrueTrue(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
If TrueFalse(c) Assertion (A) is true but reason (R) is false.
If FalseTrue(d) Assertion (A) is false but reason (R) is true.
If FalseFalse(e) Both Assertion and Reason are false.

Now, lets practice some Assertion Reason Questions of Physics: Chapter 11 Dual Nature of Radiation and Matter

For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.

Question.1.
Assertion: In process of photoelectric emission, all emitted electrons do not have same kinetic energy.
Reason: If radiation falling on photosensitive surface of a metal consists of different wave length then energy acquired by electrons absorbing photons of different wave lengths shall be different.

Ans.1. (b)
Both statement I and II are true; but even it radiation of single wavelength is incident on photosensitive surface, electrons of different KE will be emitted.

Question.2.
Assertion: Though light of a single frequency (monochromatic) is incident on a metal, the energies of emitted photoelectrons are different.
Reason: The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.

Ans.2. (a)
When a light of single frequency falls on the electrons of inner layer of metal, then this electron comes out of the metal surface after a large number of collisions with atom of it’s upper layer.

Question.3.
Assertion: The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.
Reason: The work function of the metal is its characteristics property.

Ans.3. (b)
The kinetic energy of emitted photoelectrons varies from zero to a maximum value. Work function depends on metal used.

Question.4.
Assertion: Photoelectric saturation current increases with the increase in frequency of incident light.
Reason: Energy of incident photons increases with increase in frequency and as a result photoelectric current increases.

Ans.4. (d)
Photoelectric saturation current is independent of frequency. It only depends on intensity of light.

Question.5.
Assertion: Photosensitivity of a metal is high if its work function is small.
Reason: Work function = hf_{o} where f_{o} is the threshold frequency.

Ans.5. (b)
Less work function means less energy is required for ejecting out the electrons.

Question.6.
Assertion: The photon behaves like a particle.
Reason: If E and P are the energy and momentum of the photon, then P=\frac{E}{c} .

Ans.6. (a)
Both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

Question.7.
Assertion: In an experiment on photoelectric effect, a photon is incident on an electron from one direction and the photoelectron is emitted almost in the opposite direction. It violate the principle of conservation of linear momentum.
Reason: It does not violate the principle of conservation of linear momentum.

Ans.7. (d)
Both the Assertion and Reason are incorrect.

Question.8.
Assertion: Two sources of equal intensity always emit equal number of photons in any time interval.
Reason: Two sources of equal intensity may emit equal number of photons in any time interval.

Ans.8. (d)
Total number of emitted photons depends on energy of each photon. The energy of photons of two sources may be different.

Question.9.
Assertion: Two photons of equal wavelength must have equal linear momentum.
Reason: Two photons of equal linear momentum will have equal wavelength.

Ans.9. (d)
To photons of equal wavelength will have equal momentum (magnitude), but direction of momentum may be different.

Question.10.
Assertion: The kinetic energy of photoelectrons emitted from metal surface does not depend on the intensity of incident photon.
Reason: The ejection of electrons from metallic surface is not possible with frequency of incident photons below the threshold frequency.

Ans.10. (b)
Both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.