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Ray Optics and Optical Instruments  Digital www.allendigital.in [ 105 ] REFLECTION OF LIGHT AT PLANE SURFACE 1. When a ray of light is incident normally on a plane mirror then the angle of reflection will be (1) 0° (2) 90° (3) 180° (4) – 90° 2. A ray is incident at 30° angle on plane mirror. What will be deviation after reflection from mirror. (1) 120° (2) 60° (3) 30° (4) 45° 3. Two plane mirrors are lying perpendicular to each other, there is lamp in between mirrors. Then number of images of lamp will be (1) 3 (2) 4 (3) 5 (4) 6 4. A man runs towards stationary plane mirror at a speed of 15 m/s. What is the speed of his image with respect to mirror :– (1) 7.5 m/s (2) 15 m/s (3) 30 m/s (4) 45 m/s 5. Figure shows two plane mirrors parallel to each other and an object O placed between them. Then the distance of the first three images from the mirror M2 will be :(in cm) 5cm 15cm O M1 M2 (1) 5, 10, 15 (2) 5, 15, 30 (3) 5, 25, 35 (4) 5, 15, 25 6. A ray gets successively reflection from two mirrors inclined at an angle of 40°. If the angle of incidence on the first mirror is 30° then the net deviation of this ray after two reflections. (1) 40° (2) 280° (3) 90° (4) 240° 7. A tall man of height 6 feet, want to see his full image. Then required minimum length of the mirror will be :- (1) 12 feet (2) 3 feet (3) 6 feet (4) Any length 8. A man is 180 cm tall and his eyes are 10 cm below the top of his head. In order to see his entire height right from toe to head, he uses a plane mirror kept at a distance of 1 m from him. The minimum length of the plane mirror required is (1) 180 cm (2) 90 cm (3) 85 cm (4)170 cm 9. Two plane mirrors are at 45° to each other. If an object is placed between them then the number of images will be (1) 5 (2) 9 (3) 7 (4) 8 REFLECTION AT SPHERICAL SURFACE 10. The focal length of a concave mirror is 50 cm. where an object be placed so that its image is two times magnified, real and inverted - (1) 75 cm (2) 72 cm (3) 63 cm (4) 50 cm 11. An object of height 7.5 cm is placed in front of a convex mirror of radius of curvature 25 cm at a distance of 40 cm. The height of the image should be - (1) 2.3 cm (2) 1.78 cm (3) 1 cm (4) 0.8 cm 12. A square of side 3 cm is placed at a distance of 25 cm from a concave mirror of focal length 10 cm. The centre of the square is at the axis of the mirror and the plane is normal to the axis. The area enclosed by the image of the wire is - (1) 4 cm2 (2) 6 cm2 (3) 16 cm2 (4)36 cm2 13. The focal length of a concave mirror is 12 cm. Where should an object of height 4 cm be placed, so that a real image of 1 cm height is formed ? (1) 48 cm (2) 3 cm (3) 60 cm (4) 15 cm 14. An object is lying at a distance of 90 cm from a concave mirror of focal length 30 cm. The position and nature of image formed by it will be (1) 45 cm, of the size of object (2) 90 cm, smaller than object (3) 30 cm, bigger than object (4) – 45 cm smaller than object 15. An object of height 1.5 cm is situated at a distance of 15 cm from a concave mirror. The concave mirror forms its real image of height 3.0 cm. The focal length of concave mirror will be (1) – 10 cm (2) – 20 cm (3) 20 cm (4) 30 cm Exercise - I
NEET : Physics [ 106 ] www.allendigital.in  Digital 16. A boy stands straight infront of a mirror at a distance of 30 cm away from it. He sees his erect image whose height is 1/5th of his real height. The mirror he is using is - (1) Plane mirror (2) Convex mirror (3) Concave mirror (4) None 17. A point object is moving on the principal axis of a concave mirror of focal length 24 cm towards the mirror. When it is at a distance of 60 cm from the mirror, its velocity is 9 cm/sec. What is the velocity of the image at that instant - (1) 5 cm/sec. (2) 12 cm/sec (3) 4 cm/sec (4) 9 cm/sec 18. A concave mirror gives an image three times as large as the object placed at a distance of 20 cm from it. For the image to be real, the focal length should be - (1) –10 cm (2) –15 cm (3) –20 cm (4) –30 cm 19. The minimum distance between the object and its real image for concave mirror is (1) f (2) 2f (3) 4f (4) Zero 20. A convex mirror has a radius of curvature of 22 cm. If an object is placed 14 cm away from the mirror then its image is formed at- (1) 6.2 cm on the front side of the mirror (2) 6.2 cm on the back side of the mirror. (3) 51.3 cm on the front of the mirror. (4) 51.3 cm on the back side of the mirror. 21. The focal length of a spherical mirror is :- (1) Maximum for red light (2) Maximum for blue light (3) Maximum for white light (4) Same for all lights 22. A point object is placed at a distance of 10 cm and its real image is formed at a distance of 20 cm from a concave mirror. If the object is moved by 0.1 cm towards the mirror, the image will shift by about. (1) 0.4 cm away from the mirror (2) 0.4 cm towards the mirror (3) 0.8 cm away from the mirror (4) 0.8 cm towards the mirror 23. The focal length of a convex mirror is 20 cm its radius of curvature will be (1) 10 cm (2) 20 cm (3) 30 cm (4) 40 cm 24. A diminished virtual image can be formed only in (1) Plane mirror (2) A concave mirror (3) A convex mirror (4) None REFRACTION AT PLANE SURFACE : SNELL'S LAWS TIR 25. The colour are characterised by which of following character of light- (1) Frequency (2) Amplitude (3) Wavelength (4) Velocity 26. The wavelength of light in two liquids 'x' and 'y' is 3500 Å and 7000Å, then the critical angle will be (1) 60° (2) 45° (3) 30° (4) 15° 27. A microscope is focused on a mark, then a glass slab of refractive index 1.5 and thickness of 6 cm is placed on the mark to get the mark again in focus, the microscope should be moved (1) 4 cm (2) 2 cm (3) 6 cm (4) 8 cm 28. Velocity of light in glass, whose refractive index w.r.t. air is 1.5, is 2 × 108 m/Sec. In a certain liquid the velocity of light is found to be 2.5 × 108 m/Sec. The refractive index of liquid w.r.t. air is (1) 0.64 (2) 0.80 (3) 1.20 (4) 1.44 29. A point source of light is place 4 m below the surface of water of refractive index 5/3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut-off all light coming out of water is. (1) 2 m (2) 6 m (3) 4 m (4) 3 m 30. When a ray of light enters a medium of refractive index μ, it is observed that the angle of refraction is half of the angle of incidence is than angle of incidence is (1) 2 cos–1(μ/2) (2) cos–1(μ/2) (3) 2 cos–1(μ) (4) 2 sin–1(μ/2)
Ray Optics and Optical Instruments  Digital www.allendigital.in [ 107 ] 31. White lightis incident on the interface of glass and air as shown in the figure. If green light is just totally internally reflected then the emerging ray in air contains Air Green Glass White (1) Yellow, orange, red (2) Violet, indigo, blue (3) All colours (4) All colours except green 32. A plane glass slab is kept over various coloured letters; the letter which appears least raised is (1) blue (2) voilet (3) green (4) red 33. A bubble in glass slab ( = 1.5) when viewed from one side appears at 5 cm and 2cm from other side, then thickness of slab is:- (1) 3.75 cm (2) 3 cm (3) 10.5 cm. (4)2.5 cm 34. A ray of light travelling in air have wavelength  , frequency n, velocity V and intensity I. If this ray enters into water than these parameters are ' , n', v' and I' respectively. Which relation is correct from following- (1)  = ' (2) n = n' (3) v = v' (4) I = I' 35. Light travels through a glass plate of thickness t and having refractive index n. If c is the velocity of light in vacuum. the time taken by the light to travel this thickness of glass is (1) t nc (2) tnc (3) nt c (4) tc n 36. A ray of light propagates from glass (refractive index = 3/2) to water (refractive index = 4/3). The value of the critical angle (1) sin–1 (1/2) (2) sin–1 8 9         (3) sin–1 (8/9) (4) sin–1 (5/7) 37. Relation between critical angles of water and glass is (1) Cw> Cg (2) Cw< Cg (3) Cw= Cg (4) Cw= Cg = 0 38. Critical angle of light passing from glass to air is minimum for (1) Red (2) Green (3) Yellow (4) Violet 39. Which of the following is used in optical fibres (1) T.I.R. (2) Scattering (3) Diffraction (4) Refraction 40. Brilliance of diamond is due to (1) Shape (2) Cutting (3) Reflection (4) T.I.R. 41. 'Mirage' is a phenomenon due to (1) Reflection of light (2) Refraction of light (3) T.I.R. of light (4) Diffraction of light 42. An object is immersed in a fluid. In order that the object becomes invisible, it should. (1) Bahave as a perfect reflector (2) Absorb all light falling on it (3) Have refractive index one (4) Have refractive index exactly matching with that of the surrounding fluid PRISM & DISPERSION 43. The angle of a glass prism is 4.5° and its refractive index is 1.52. The angle of minimum deviation will be – (1) 1.5° (2) 2.3° (3) 4.5° (4) 2° 44 A ray of light passes through equilateral Prism ( =1.5) such that angle of incidence is equal to angle of emergence and the later is equal to 3/4th of Prism angle. The angle of deviation is (1) 60° (2) 30° (3) 45° (4) 120° 45. Prism angle of glass prism is 10°. It's refractive index of red and violet colour is 1.51 and 1.52 respectively. Then its dispersive power will be. (1) 0.015 (2) 0.020 (3) 0.011 (4) 0.019 46. If the refractive indices of crown glass for red, yellow and violet colours are 1.5140, 1.5170 and 1.5318 respectively and for flint glass these are 1.6434, 1.6499 and 1.6852 respectively, then the dispersive powers for crown and flint glass are respectively. (1) 0.034 and 0.064 (2) 0.064 and 0.034 (3) 1.00 and 0.064 (4) 0.034 and 1.0
NEET : Physics [ 108 ] www.allendigital.in  Digital 47. A thin Prism P1 with angle 4° and made from glass of refractive index 1.54 is combined with another thin Prism P2 made from glass of refractive index 1.72 to produce dispersion without deviation. The angle of Prism P2 is (1) 5.33° (2) 4° (3) 3° (4) 2.6° 48. The angle of minimum deviation measured with a prism is 30° and the angle of prism is 60°. The refractive index of prism material is - (1) 2 (2) 2 (3) 3 2 (4) 4 3 49. Angle of prism is A and its one surface is silvered. Light rays falling at an angle of incidence 2A on first surface return back through the same path after suffering reflection at second silvered surface. Refractive index of the material of prism is (1) 2 sin A (2) 2 cos A (3) 1 2 cosA (4) tanA 50. A ray falls on a prism ABC (AB = BC) and travels as shown in figure. The minimum refractive index of the prism material should be A C B 90° 90° (1) 4 3 (2) 2 (3) 1.5 (4) 3 51. For a prism, graph between angle of deviation () and angle of incidence will be (1) y x  O i (2) y x  O i (3) y x  O i (4) y x  O i 52. Three prisms 1,2 and 3 have the prism angle A = 60°, but their refractive indices are respectively 1.4, 1.5 and 1.6. If  1,  2, 3, be their respective angles of deviation then :– (1) 3 > 2 >  1 (2) 1 > 2 > 3 (3) 1 = 2 = 3 (4) 2 > 1 > 3 53. Rainbow is formed due to :- (1) Scattering & refraction (2) Internal reflection & dispersion (3) Reflection only (4) Diffraction and dispersion 54. The refractive index of the material of a prism is 2 and its refracting angle is 30°. One of the refracting surfaces of the prism is silvered. A beam of monochromatic light entering the prism from the other face will retrace its path after reflection from the silvered surface if its angle of incidence on the prism is :– (1) 60° (2) 0° (3) 30° (4) 45° REFRACTION AT SPHERICAL SURFACES 55. A point object O is placed in front of a glass rod having spherical end of radius of curvature 30 cm. The image formed would be O Air 15cm Glass 30cm (1) 30 cm left (2) infinity (3) 1 cm to the right (4) 18 cm to the left 56. A spherical surface of radius of curvature R separates air (refractive index 1.0) from glass (refractive index 1.5). The centre of curvature is in glass. A point object P placed in air is found to have a real image Q in the glass. The line PQ cuts the surface at a point O and PO = OQ. The distance PO is equal to (1) R (2) 3 R (3) 2 R (4) 5 R LENSES 57. Two convex lens of focal length 20 cm and 25 cm are placed in contact with each other, then power of this combination is – (1) + 1 D (2) + 9 D (3) – 1 D (4) – 9 D