Page 1 - Worksheet 2

WORK SHEET -2, PHYSICS

CLASS 12, CHAPTER 9 (RAY OPTICS AND OPTICAL INSTRUMENTS)

REFRACTION OF LIGHT

1 A converging lens is used to form an image on a screen. When the upper half of the
lens is covered by an opaque screen.
(a) half the image will disappear.
(b) incomplete image will be formed.
(c) intensity of image will decrease but complete image is formed.
(d) intensity of image will increase but image is not distinct.
2 In optical fibres, the refractive index of the core is
(a) greater than that of the cladding.
(b) equal to that of the cladding.
(c) smaller than that of the cladding.
(d) independent of that of cladding
3 Air bubble in water behaves as
(a) sometimes concave, sometimes convex lens
(b) concave lens
(c) convex lens
(d) always refracting surface
4 We combine two lenses, one is convex and other is concave having focal lengths /,
and f2 and their combined focal length is F. Combination of the lenses will behave
like concave lens, if
(a) f 1 > f 2
(b) f 1 = f 2
(c) f 1 < f 2.
(d) f 1 ≤ f 2
5 The focal length of a biconvex lens of radii of each surface 50 cm and refractive
index 1.5, is
(a) 40.4 cm
(b) 75 cm
(c) 50 cm
(d) 80 cm
6 A metal coin is at bottom of a beaker filled with a liquid of refractive index = 4/3 to
height of 6 cm. To an observer looking from above the surface of liquid, coin will
appear at a depth
(a) 1.5 cm
(b) 6.75 cm
(c) 4.5 cm
(d) 7.5 cm
7 A convex lens of refractive index 32 has a power of 2.5 D in air. If it is placed in a
liquid of refractive index 2 then the new power of the lens is