Refraction of light at spherical surfaces of lenses

Important questions for ISCE Board exam (Physics) of Feb 2020
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1. IMPORTANT THEORY QUESTIONS

Refraction of Light at Spherical Surfaces : Lenses

Prepared by : Mukesh N Tekwani
Email: [email protected]

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 n
2 /v - n
1 /u = (n
2 - n
1 )/r 5 Derive
5 Derive lens maker’s formula 1/f = (n - 1) (1/R
1 - 1/R
2 ) 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 n
1 (rarer medium), n
2 (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 f
1 and f
2 are placed
in contact. Show that 1/f = 1 / f
1 - 1 / f
2 . Discuss the nature of the combined
lens when f
1 > f
2 , f
1 < f
2 , and f
1 = f
2 .
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 P
1 and P
2 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) Mukesh N Tekwani