 # WBJEE: Important Questions and Preparation Tips – Ray Optics

Find chapter notes of chapter Ray Optics for WBJEE Entrance Examination 2018. When exams are around the corner, all students want to cover more and more syllabus in less time. Students can do this by revising only chapter notes of the concerned subject. These chapter notes contain important formulae, concepts and previous years solved questions.

Oct 23, 2017 15:46 IST WBJEE 2018: Ray Optics

In this article we bring to you chapter notes of chapter Ray Optics for WBJEE Entrance Examination 2018. About 2-3 questions are always asked from this chapter in WBJEE Entrance Examination.

These chapter notes include all important concepts and formulae of all topics of chapter Ray Optics like reflection, refraction, Snell’s law, Laws of refraction, mirror equation, magnification, Total Internal reflection, combination of lens, refraction through a prism etc. Some solved questions from previous year WBJEE Examination are also included in these chapter notes which will help you to understand the difficulty level of the coming WBJEE Examination 2018.

These notes can be used as a quick revision material to study important concepts instead of revising the complete chapter just before the examination.

West Bengal Joint Entrance Examination (WBJEE) is a state level common entrance test organized by West Bengal Joint Entrance Examinations Board for admission to the Undergraduate Level Engineering and Medical Courses through a common entrance test in the State of West Bengal.

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Some previous years solved questions are given below:

Question 1:

A luminous object is separated from a screen by distance d. A convex lens is placed between the object and the screen such that it forms a distinct image on the screen. The maximum possible focal length of this convex lens is

(A) 4d

(B) 2d

(C) d/2

(D) d/4

Solution 1:

From the lens displacement method we can deduce that, the maximum possible focal length of the convex lens is d/4.

Hence, the correct option is (D).

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Question 2:

An object is placed 30 cm away from a convex lens of focal length 10 cm and a sharp image is formed on a screen. Now a concave lens is placed in contact with the convex lens. The screen now has to be moved by 45 cm to get a sharp image again. The magnitude of focal length of the concave lens is (in cm)

(A) 72

(B) 60

(C) 36

(D) 20

Solution 2: Hence, the correct option is (D).

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Question 3:

A glass slab consists of thin u iform layers of progressively decreasing refractive indices RI (see figure) such that the RI of any layer is μ-mΔμ. Here μ and Δμ denote the RI of 0th layer and the difference in RI between any two consecutive layers, respectively. The integer m = 0, 1, 2, 3..... denotes the numbers of the successive layers. A ray of light from the 0th layer enters the 1st layer at an angle of incidence of 30°. After undergoing the mth refraction, the ray emerges parallel to the interface. If μ = 1.5 and Δμ = 0.015, the value of m is (A) 20

(B) 30

(C) 40

(D) 50

Solution 3:

By using Snell’s law: Hence, the correct option is (D).

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Question 4:

A ray of light strikes a glass plate at an angle of 60°. If the reflected and refracted rays are perpendicular to each other. the refractive index of glass is Solution 4: Hence, the correct option is (D).

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Question 5:

Light travels through a glass plate of thickness t and having refractive Index µ If c be the velocity of light in vacuum. time taken by the light to travel through this thickness of
glass is Solution 5: Hence, the correct option is (C).

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