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.

**About the exam:**

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.

**Important Questions and Preparation Tips – Work, Power and Energy**

**Important Concepts:**

**Important Questions and Preparation Tips – Centre of Mass**

**Some previous years solved questions are given below:**

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**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).

**Important Questions and Preparation Tips – Rotational Motion**

**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).

**Important Questions and Preparation Tips – Gravitation**

**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 0^{th} layer enters the 1^{st} layer at an angle of incidence of 30°. After undergoing the m^{th} 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).

**Important Questions and Preparation Tips – Simple Harmonic Motion**

**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).

**Important Questions and Preparation Tips – Laws of Motion**

**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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