# Assertion Reason Physics Chapter 9 Ray Optics and Optical Instruments

Questions of Assertion Reason of Physics Chapter 9 Ray Optics and Optical Instruments CBSE Class 12 are very simple to understand as this chapter deals with Ray Optics and Optical Instruments. To solve assertion reason type questions of Physics, a deeper understanding of concept about Reflection of Light by Spherical Mirrors, Refraction, Total Internal Reflection, Refraction at Spherical Surfaces and by Lenses, Refraction through a Prism and Optical Instruments 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 9 Ray Optics and Optical Instruments

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: Plane mirror may form real image.
Reason: Plane mirror forms virtual image, if object is real.

Ans.1. (b)
Both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

Question.2.
Assertion: The focal length of the convex mirror will increase, if the mirror is placed in water.
Reason: The focal length of a convex mirror of radius R is equal to , f = R/2.

Ans.2. (d)
Focal length of the spherical mirror does not depend on the medium in which it placed.

Question.3.
Assertion: The image formed by a concave mirror is certainly real if the object is virtual.
Reason: The image formed by a concave mirror is certainly virtual if the object is real.

Ans.3. (c)
The image of real object may be real in case of concave mirror.

Question.4.
Assertion: The image of an extended object placed perpendicular to the principal axis of a mirror, will be erect if the object is real but the image is virtual.
Reason: The image of an extended object, placed perpendicular to the principal axis of a mirror, will be erect if the object is virtual but the image is real.

Ans.4. (b)
Both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

Question.5.
Assertion: An object is placed at a distance off from a convex mirror of focal length f its image will form at infinity.
Reason: The distance of image in convex mirror can never be infinity.

Ans.5. (d)
Both the Assertion and Reason are incorrect.

Question.6.
Assertion: The image of a point object situated at the centre of hemispherical lens is also at the centre.
Reason: For hemisphere Snell’s law is not valid.

Ans.6. (c)
The rays from centre of hemisphere cut at the centre after refraction – Snell’s law is valid in each case of refraction.

Question.7.
Assertion: The focal length of an equiconvex lens of radius of curvature R made of material of refractive index μ = 1.5, is R.
Reason: The focal length of the lens will be R/2.

Ans.7. (c)
Assertion is correct but Reason is incorrect.

Question.8.
Assertion: If the rays are diverging after emerging from a lens; the lens must be concave.
Reason: The convex lens can give diverging rays.

Ans.8. (d)
If the rays cross focal point of convex lens, they become diverging.

Question.9.
Assertion: The resolving power of a telescope is more if the diameter of the objective lens is more.
Reason: Objective lens of large diameter collects more light.

Ans.9. (a)
RP α diameter of objective.

Question.10.
Assertion: The optical instruments are used to increase the size of the image of the object.
Reason: The optical instruments are used to increase the visual angle.

Ans.10. (d)
Both the Assertion and Reason are incorrect.