Deduce the relation between n , u , v , R for refraction at a spherical surface, where the symbols have their usual meaning.

The following figure shows the formation of image I of an object O on the principal axis of a convex surface with the centre of curvature C . Since the aperture is small the length of N M will be taken to be nearly equal to the length of the perpendicular from the point N on the principal axis. For small angles tan ∠ N O M ≈ ∠ N O M = M N O M tan ∠ N C M ≈ ∠ N C M = M N M C tan ∠ N I M ≈ ∠ N I M = M N M I Here i = ∠ N O M + ∠ N C M = M N O M + M N M C and r = ∠ N C M - ∠ N I M = M N M C - M N M I According to snell's law n 1 sin i = n 2 sin r For small angles, it can be written as n 1 i = n 2 r n 1 M N O M + M N M C = n 2 M N M C - M N M I ⇒ n 1 1 O M + 1 M C = n 2 1 M C - 1 M I ⇒ n 1 O M + n 1 M C = n 2 M C - n 2 M I ⇒ n 1 O M + n 2 M I = n 2 M C - n 1 M C ⇒ n 1 O M + n 2 M I = n 2 - n 1 M C According to the Cartesian sign convention O M = - u , M I = + v , M C = + R ⇒ n 1 - u + n 2 v = n 2 - n 1 R n 2 v - n 1 u = n 2 - n 1 R

For which position of the object, magnification of convex lens is -1 (minus one)?

Magnification ( m ) for lens = h h ' . In a convex lens, when object is in front of the lens at 2 F 1 , an inverted image of the same size as of object is formed at 2 F 2 . Since, the top of the axis is + ve and the bottom of the axis is - ve, we have m as negative. Therefore, m = - 1 .

What is myopia? How to rectify it?

Myopia also known as near or short-sightedness is a defect of vision. A person suffering from myopia can see the nearby objects clearly but is unable to see the far off objects distinctly. Thus, the image of a far lying object is formed in front of the retina and not on it. Myopia is caused: (a) Due to the elongation of the eyeball and (b) Due to a decrease in the focal length of the eye lens. Myopia can be rectified using a concave lens of suitable focal length.

Two lenses of power + 1 . 5 D and - 0 . 5 D are kept in contact on their principal axis. What is the effective power of combination?

The power of the lens is additive in nature. The effective power is given by the sum of powers of two lenses. It is given by : P = P 1 + P 2 P = + 1 . 5 D - 0 . 5 D P = 1 . 0 D So, the effective power of the combination is 1 D .

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Karnataka Board-2019>Q 5

MEDIUM

12th Karnataka Board

IMPORTANT

Earn 100

Draw the ray diagram for formation of image in a simple microscope.

Important Questions on Ray Optics and Optical Instruments

HARD

12th Karnataka Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Karnataka Board-2019>Q 6

Derive “Lens maker’s” formula.

MEDIUM

12th Karnataka Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Karnataka Board-2020>Q 7

Why does sky appear blue?

HARD

12th Karnataka Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Karnataka Board-2020>Q 8

Mention a method to increase the resolving power of a microscope.

MEDIUM

12th Karnataka Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Karnataka Board-2020>Q 9

Arrive at the relation between the focal length and radius of curvature of a spherical concave mirror.

HARD

12th Karnataka Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Karnataka Board-2020>Q 10

At what angle should a ray of light be incident on the face of an equilateral prism, so that it just suffers total internal reflection at the other face? The refractive index of the material of the prism is $1.5$ .

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