How to Prepare NSEP for Ray Optics

How To Prepare NSEP For Ray Optics

Edited By Ramraj Saini | Updated on Nov 14, 2022 03:29 PM IST

Optics is part of NCERT Class 12, Physics syllabus. The unit Optics is divided into two chapters, Ray Optics And Optical Instruments and Wave Optics. Total weightage of the unit Optics in Past six years is 14 per cent out of which 11 per cent questions are from Ray Optics. Read on to know the syllabus, formulas, some previous year NSEP questions and study materials for Ray Optics

How To Prepare NSEP For Ray Optics

NSEP Syllabus For Ray Optics

The topics that fall under NSEP syllabus for Ray Optics are: Reflection of light, spherical mirrors, mirror formula, refraction of light, total internal reflection(TIR) and its applications, optical fibres, refraction at spherical surfaces, lenses, thin lens formula, lensmaker's formula, power of a lens, magnification,, combination of thin lenses in contact, prism, refraction through prism, scattering of light and its application, optical instruments: microscopes and astronomical telescopes (reflecting and refracting) and their magnifying powers.

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Ray Optics Important Formulas

The formulas from Ray Optics Chapter are listed here. These may be helpful in solving NSEP questions and NSEP previous year papers.

Formula

Description

1/v+1/u=1/f-Mirror Equation

v-object distance

u- image distance from the pole of the mirror.

f- focal length

f=R/2, R-radius of curvature

Magnification -

$h_{i}=$ height of the image

$h_{o}=$ height of the object

If a prism of refractive index n2is placed in a medium with refractive index n1. then

$\boldsymbol{\frac{n_2}{n_1} = \frac{\sin \left ( \frac{D _{m}+A}{2} \right )}{\sin \left ( A/2 \right )}}$

A- angle of the prism

Dm- angle of minimum deviation

Thin lens formula

$\frac{1}{v}-\frac{1}{u}= \frac{1}{f}$

Lens makers formula

$\boldsymbol{\frac{1}{f}= \left ( \frac{\mu _{2}}{\mu _{1}}-1 \right )\left ( \frac{1}{R_{1}}- \frac{1}{R_{2}}\right )}$

$\mu _{1}=$ the refractive index of the medium $\mu _{2}=$ the refractive index of the lens

$R_{1}\, and \, R_{2}$ are the radius of curvature

Power of a lens

$\boldsymbol{P=\frac{1}{f}}$

P -power

f - focal length in metres

For a a simple microscope $m=1+ \frac{D}{f}$

For a compound microscope $m=m_e \times m_0$

D = 25 cm is the least distance of distinct vision

is magnification of the eyepiece.

is magnification of the objective.

Incase of a telescope

$m=\frac{\beta}{\alpha}=\frac{f_o}{f_e}$

? is the angle subtended by eyepiece at the image

ɑ is the angle subtended at the eye by the object

NSEP Previous Year Questions From Ray Optics

Questions from the topic reflection, refraction and optical instruments are covered here. All the topics of Ray Optics are important and questions can be expected from any of the topics. So preparing the entire chapter is a must. There is no possibility of skipping.

Q-1-A small fish, 4 cm below the surface of a lake, is viewed through a thin converging lens of focal length 30 cm held 2 cm above the water surface. Refractive index of water is 1.33. The image of the fish from the lens is at a distance of (NSEP 2017)

(a) 10 cm (b) 8 cm (c) 6 cm (d) 4 cm

Q-2- A horizontal ray of light passes through a prism of refractive index 1.5 and apex angle 4o and then strikes a vertical plane mirror placed to the right of the prism. If after reflection, the ray is to be horizontal, then the mirror must be rotated through an angle (NSEP 2017)

(a) 1 o clockwise (b) 1 o anticlockwise (c) 2 o clockwise (d) 2 o anticlockwise

Q-3- Rays from an object immersed in water (µ = 1.33) traverse a spherical air bubble of radius R. If the object is located far away from the bubble, its image as seen by the observer located on the other side of the bubble will be(NSEP 2017)

Ray-Optics

(a) virtual, erect and diminished (b) real, inverted and magnified (c) virtual, erect and magnified (d) real, inverted and diminished

Q-4- The aperture diameter of a plano-convex lens is 6 cm and its thickness is 3 mm. If the speed of light through its material is v = 2 108 m/s, the focal length of the lens is(NSEP 2018)

(a) 40 cm. (b) 35 cm. (c) 30 cm. (d) 20 cm.

Q-5-A thin hollow equiconvex lens, silvered at the back, converges a beam of light parallel to the principal axis at a distance 0.2 m. When filled with water (n=4/3 ), the same beam will be converged at a distance of (NSEP 2018)

(a) 0.40 m. (b) 0.20 m. (c) 0.12 m. (d) none of the above

Q-6- Q-2- A converging lens of focal length 40 cm is fixed at 40 cm in front of a screen. An object placed 120 cm from the fixed lens is required to be focused on the screen by introducing another identical lens in between. The second lens should be placed at a distance x from the object where x is(NSEP 2018: One or more option correct)

(a) 40 cm. (b) 50 cm. (c) 140 cm. (d) 150 cm.

Q-7- The optical powers of the objective and the eyepiece of a compound microscope are 100 D and 20 D respectively. The microscope magnification is equal to 50 when the final image is formed at d = 25 cm i.e., the least distance of distinct vision. If the separation between the objective and the eyepiece is increased by 2 cm, the magnification of the microscope will be(NSEP 2021)

(a) 62 (b) 50 (c) 38 (d) 25

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