This document contains 15 important theory questions about refraction of light at spherical surfaces and lenses. It includes questions about sign convention in optics, the optical center of a lens, focal length of concave and convex lenses, lens maker's formula, derivation of expressions for refraction at single spherical surfaces and thin lens combinations, linear magnification by a lens, location of a virtual image formed by a convex lens based on focal length, dependence of focal length on wavelength, definition and unit of power of a lens, definition of 1 dioptre, formula for combined power of two lenses in contact, and laws governing image formation by lenses. The questions cover key concepts like derivation, definition, diagrams, formulas, and image formation.

1. IMPORTANT THEORY QUESTIONS
Refraction of Light at Spherical Surfaces : Lenses
Prepared by : Mukesh N Tekwani
Email: scitechgen@outlook.com
Sr
No Question
Marks Keyword(s)
1 What is the coordinate geometry sign convention for optics? 2 Sign
convention
2 Define the term ‘optical centre of a lens’. 2 Optical centre
3 What is meant by focal length of a concave lens? 2 Focal length
4 Derive the relation n2/v - n1/u = (n2 - n1)/r 5 Derive
5 Derive lens maker’s formula 1/f = (n - 1) (1/R1 - 1/R2) 5 Derive
6 Starting with an expression for refraction at a single spherical surface,
obtain an expression for lens maker’s formula.
3 Lens Maker’s
formula
7 Obtain an expression for refraction at a single convex spherical surface i.e.,
the relation between n1 (rarer medium), n2 (denser medium), the object
distance u, the image distance v and radius of curvature.
3 Derive
8 Two thin lenses (convex and concave) of focal lengths f1 and f2 are placed
in contact. Show that 1/f = 1 / f1 - 1 / f2. Discuss the nature of the combined
lens when f1 > f2, f1 < f2, and f1 = f2 .
5 Derive
9 Define linear magnification produced by a lens. Derive an expression for
linear magnification in terms of object distance, image distance and focal
length.
3 Define, Derive
10 A convex lens forms a virtual image of an object. In terms of focal length,
where is the object?
1 Diagram
11 How does focal length of a convex lens change with increase in wavelength
of incident light?
1 Focal length
12 Define the term ‘power of a lens’. State the unit of power of a lens. 2 Define
13 What is 1 dioptre? 1 Define
14 If P1 and P2 are the powers of two lenses, then what is the combined power
of both lenses kept in contact.
1 Formula
15 State the laws by which image formation by lenses takes place. 5 Image
formation
(c)M
ukesh
N
Tekw
ani