Refraction at plane surface and Prism Questions used for discussion

Refraction at plane surface and Prism Questions used for discussion 1. A ray of light is incident on the surface of separation of a medium with a velocity of light (c=x10 8 ms -1 ) at an angle 45 0 and is refracted in the medium at an angle 0 0. What will be the velocity of light in the medium: (1) 1.96X10 8 ms -1 ().1X10 8 ms -1 ().18X10 8 ms -1 (4).X10 8 ms -1. A ray of light is travelling from medium A to medium B. The angle of incidence is i and that of refraction is r. Graph between sin(i) and sin(r) is as shown in Figure below. We can conclude the following (i) Speed of light in medium B is three-fourth of that in medium A. (ii) Total internal reflection cannot take place. (iii) Refractive index of medium B is greater than that of medium A. Correct conclusions are (1)Only (i) and (ii) () Only (ii) and (iii) () (i), (ii) and (iii) (4) Only (i) and (iii). Given refractive index of glass with respect to air is a n g = / and that of water with respect to air a n w = 4/, the refractive index of glass with respect to water is (1) 8/9 () 9/8 () (4) 1/ 4. A vessel of height h is filled with a liquid of refractive index n 1 to a height h/ and the upper half of the vessel is filled with a liquid of refractive index n. The apparent depth of the vessel as seen along the normal is (1) n1n h n + n 1 h n1n () n 1 + n h n 1 + n () n1n n 1n (4) h n 1 + n

5. A ray of light passes through four transparent media with refractive indices 1 and 4 as shown in fig. The surfaces of all media are parallel. If the emergent ray CD is parallel to the incident ray AB, we must have µ 1 µ µ A A C D µ 4 (1) 1 = () = () = 4 (4) 4 = 1 6. An ink dot on a paper placed on a table top is viewed from a distance of 0 cm above it with the help of a telescope. A 16 cm thick glass slab is placed on the ink dot. By what distance the telescope should be raised to refocus the ink dot? The refractive index of glass is 1.6. (1) cm () 4 cm () 5 cm (4) 6 cm 7. Consider the situation shown in the figure. The bottom of the vessel is a plane mirror, S is a small fish located at a height of H/ from the plane of the mirror, T is a human eye located at a height of H from the surface of water. The distances at which the fish sees the images of the eye (with respect to its position) are T 1 (1) H n + above and H n + below H 1 () H 1 + above and H 1 + below n n 1 () above and H n + H n + below H S (H/) (4) H + above and H + below n n 8. A, B and C are three optical media of respective critical angles C 1, C and C. Total internal reflection of light can occur from A to B and also from B to C but not from C to A. Then the correct relation between critical angles is: (1) C 1 >C >C () C 1 = C = C () C > C 1 > C (4) C 1 <C <C 9. What is the critical angle, C for calcite (=1.5) immersed in oil (=1.1)? (1) C = tan ( 1.1 1.5) 1 () C = cos ( 1.1 1.5) () C = sin ( 1.5 1.1) (4) C = sin ( 1.1 1.5)

10. The minimum angle of deviation of a prism of refractive index 1.7 is equal to its refracting angle. What is the angle of prism? (1) 40 0 () 45 0 () 60 0 (4) 0 0 11. A ray of light is incident on one refracting face of a prism of angle 75 0. It passes through the prism and is incident on the other face at critical angle. If the refractive index of the material of the prism is, then the angle of incidence on the first face is: (1) 0 0 () 45 0 () 60 0 (4) 75 0 1. The dispersive power of the material of the prism for which refractive index for violet and red colours are n v = 1.54, n r = 1.514 respectively is 1) 0.05 ) 0.04 ) 0.019 4) 0.015 1. A crown glass prism of 6 0 is cemented with a flint glass prism to form a pair which produces dispersion without deviation. If the refractive index of the crown glass prism is 1.5 and that of flint glass 1.66, then the angle of flint glass pair should be 4.7 0 () 5.7 0 () 6.7 0 (4) 7.7 0 14. Light appears to travel in straight line because 1) The frequency of light is very small ) Light consists of very small particles ) The wavelength of light is very small 4) The velocity of light is different for different colours. 15. When light is refracted through a prism, maximum deviation occurs when the following conditions are satisfied (i) the ray is incident grazing the first face (ii) the ray emerges out grazing its second face

Options (1)Only in case (i) () Only in case (ii) () In both the cases (4) Not under these cases 16. A man is swimming underwater with undisturbed surface. Looking up at a bright sky through the water, he will see (1)a bright patch directly above whose angular size is independent of the depth of the swimmer ()a shining surface of the water () just darkness (4) a bright patch directly above whose angular size depends upon the depth of the swimmer Extra questions 17. A bulb is placed at a depth of 7 in water and a floating opaque disc is placed over the bulb so that the bulb is not visible from the surface. The radius of the disc should be at least : (given refractive index of water is 4/) (1) 4m () 6m () 7m (4) 1m 18. A prism ABC of angle 0 0 has its face AC silvered. A ray of light incident at an angle of 45 0 at the face AB is found to retrace its path. The refractive index of the material of the prism is (1) 1.5 () () (4) /

19. The difference between angle of minimum deviation of violet and red rays in the spectrum of white light is 0. If the angle of minimum deviation of mean ray is 40 0, the dispersive power of the material of the prism is (1) 0.04 () 0.05 () 0.5 (4) 0.05 0. In a prism, the angle of incidence for which the emergent ray grazes the boundary is given by (i 1 ) min. Consider the following changes. (a) if the angle of incidence is greater than (i 1 ) min (b) at an angle greater than (i 1 ) min if the angle of prism is changed (c) at an angle greater than (i 1 ) min if the refractive index of material is changed The light will come out of the prism (1) Only in case of (a) () Only in case of (b) () Only in case (C) (4) In case of (a), (b) and (c)

Practice questions 1. Velocities of light in water and glass have which of the following relations? (1) The velocities in both the media are equal to that in vacuum. () The velocities in both the media are the same but less than that in vacuum. () The velocity in water is more than that in glass but less than that in vacuum. (4) The velocity in water is less than that in both glass and vacuum.. Light travels through a glass plate of thickness d and refractive index n. If c is the velocity of light in vacuum, the time taken by light to travel this thickness of glass is (1) d/nc () dnc () nd/c (4) dc/n. A ray of light from a denser medium strikes a rarer medium at angle of incidence i (fig). The reflected and refracted rays make an angle of 90 with each other. The angles of reflection and refraction are r and r '. The refractive index is (1) tan(r) () cot(i) () ssec(r) (4) cosec(i) A DENSER BARER N i B r r' N C D 4. A ray of light of wavelength 70 nm is refracted into a medium of refractive index 1.5. The wavelength of light in the medium is (1) 1080 nm () 70 nm () 480 nm (4) 600 nm 5. A ray of light travelling from air to water. (Refractive index of water = 4/). The angle of incidence is 5. The deviation of the ray is (1) 0 () 16 1 sin 50 sin 50 () 50 sin (4) sin 1 1.5 50 1.5 6. A glass slab of thickness 4 cm contains the same number of waves as 5 cm water can contain, when both are traversed by the same monochromatic light. If the refractive index of water is 4/, refractive index of glass is (1) 5/ () 5/4 () 16/15 (4) 1.5

7. A light beam passing from air into a liquid suffers a deviation of 15 at the interface when incident at an angle of 60. The refractive index of the liquid is (1) () () 8. A ray of light passes through a slab (n = 1.5) of thickness d. The angle of refraction 60. If the speed of light in vacuum is c, then the time taken to cross the slab will be (1) d () c 4d (4) c d () c d c (4) 9. Red, yellow and blue light are made to incident on a glass slab of thickness t, one after the other at an angle of incidence θ (θ is small). Then the lateral shift produced is (1) maximum for red () minimum for red () same for red, yellow and blue (4) minimum for violet 10. A tank contains a glass slab 8 cm thick and of refractive index 1.6. Above this a thin beaker containing oil to a height of 4.5 cm is placed. Upon this water to a height of 6 cm 4 floats. (refractive index = ). To an observer looking along the normal, a mark at the bottom of the glass slab appears to be raised by 6 cm from the bottom of the slab. The refractive index of oil is (1) 0.8 () 1. () 1.5 (4) 1.8 11. A bubble lies in a glass slab at an apparent depth of 10 cm. If the refractive index of glass be 1.5, the real depth of the bubble is 10 (1) cm 1.5 1.5 () cm 10 () 11.5cm (4) 15.0cm

1. A small object is placed at a distance of 0 cm from a glass block 10 cm thick. The farther side of the glass block is silvered. The image appears to be. cm behind the silvered face of the block. The refractive index of glass is (1) 1.49 () 1.51 () 1.59 (4) 1.48 1. Imagine that a fish inside water and a bird in the sky are looking at each other. Then, (1) to the fish the bird appears to be higher than it actually is () to the fish the bird appears to be lower than it actually is () to the bird the fish appears to be at lesser depth than it actually is (4) (1) and () 14. A ray of light travels from a denser to a rarer medium. The critical angle for two media is C. The maximum possible deviation of the ray will be (1) ( π C ) () ( π +C ) () C (4) ( π C ) 15. A ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence of 45. The ray undergoes total internal reflection. If n is the refractive index of the medium with respect to air, select the possible value(s) of n from the following (1) 1.6 () 1. () 1.4 (4) 1. 16. Two transparent media A and B are separated by a plane boundary. The speed of light in medium A is.0 8 8 10 m / s and in medium B is.5 10 m / s. The critical angle for which a ray of light from A to B is totally internally reflected is 1 (1) sin 1 () sin 1 4 () sin 1 4 (4) sin 1 5 9 17. If µ for water is 4/ and that of a given slab immersed in it is 5/, the value of the critical angle for a ray of light tending to go from glass to water is (1) sin 1 4 () sin 1 5 () sin 1 4 5 (4) none of these

18. Two media are separated by a plane surface. Speed of light in one medium is 10 1.5 10 cm sec. Deduce the critical angle for a ray going from the first medium into the second: (1) 1 sin 1 () 5 sin 1 () 6 5 sin 1 (4) 1 sin 1 1 19. A ray of light travelling from glass to air. (Refractive index of glass = 1.5). The angle of incidence is 50. The deviation of the ray is (1) 0 () 80 1 sin 50 () 50 sin 1.5 sin 50 (4) sin 1 50 1.5 0. A ray of light undergoes deviation of 0 when incident on an equilateral prism of 60 refractive index is. The angle made by ray inside the prism with the base of the prism (1) zero () 0 () 45 (4) 1. A ray of light is incident normally on one of the faces of a prism of apex angle 0 and 60 refractive index. The angle of deviation of the ray in degree is (1) 15 () 0 () 45 (4). The refractive index of an equilateral prism is. The angle of incidence at which the deviation is minimum would be (1) 0 45 () 60 () 0 (4) none of these

. A ray of light is incident on one face of an equilateral prism at an angle of 60 0. The deviation suffered by the ray is (the prism is in minimum deviation position) (1)45 0 () 60 0 ()0 0 (4) 15 0 4. A ray of light is incident normally on a face AB of a glass prism (n g = 1.5) as shown. A liquid of refractive index n is placed on the face AC of the prism. For a liquid A 60 0 C normally incident ray on the face AB, the limits of n for which total internal reflection takes place at the face AC is 90 B (1) n > () n < 4 () n > (4) n < 5. A ray of light is incident perpendicular to one of the faces of an equilateral prism. The ray emerges out of the second face when the refractive index of the prism material P is (1) () 1.15 () more than 1.15 (4) less than 1.15 B A r Q C 6. White light is passed through a prism of angle 5. If the refractive indices for the red and blue colours are 1.641 and 1.659 respectively, what is the angle of dispersion between them? (1) 5 () () 0. 09 (4) 0.9 7. If the deviation suffered the red yellow and blue light when it passé through a small angled prism is.84 0,.8 0 and.7 0 respectively then the dispersive power of the material of the prism is 1) 0.9 ) 0.7 ) 0.19 4) 0.6

8. The dispersive power of the material of the prism if n v = 1.54, n r = 1.514 is ) 0.05 ) 0.04 ) 0.019 4) 0.015 9. Dispersive power depends upon: (1) the shape of prism () angle of prism () height of prism (4) material of prism 0. A small angle of prism produces a minimum deviation of for a light ray. If the dotted half of the prism is knocked off, the same ray will (1) suffer a deviation of 4 A () suffer a deviation of () suffer a deviation of 1 (4) will not emerge out of prism B C 1. The deviation of a ray due to a small angled prism of refractive index 4n and angle A is δ 1 and that due to another small angled prism of refractive index n and angle A is δ. Given n = 1.5, δ 1 and δ are related as (1) δ = δ 1 () δ > δ 1 () δ < δ 1 (4) δ = δ 1. A thin prism P 1 with angle 4 and made from glass of refractive index 1.54 is combines with another thin prism P made from glass of refractive index 1.7 to produce dispersion without deviation. The angle of the prism P is (1) 5. () 4 () (4).6

. An achromatic prism is made by combination of two prisms P ( µ = 1. 5, µ 1 515 ) and P ( = 1. 666, µ 1 650 ) µ. If the angle of prism P 1 is F C =. prism P would be: 1 F C =. 10, then the angle of (1) 5 () 7. 8 () 10. 6 (4) 0 4. When white light is passed through a prism, it undergoes dispersion because (1) light has seven wavelengths () prism is of triangular shape () refractive index of the prism material is different for different colours (4) velocity of light is same in the prism as well in air. 5. The refractive index of a glass slab depends upon (1) the colour of the incident light () the intensity of the incident light () the angle of incidence (4) the thickness of the glass slab 6. The brilliance of diamond is (1) entirely due to refractive index () entirely due to total internal reflection () partly due to total internal reflection (4)none of the above 7. The largest angle of minimum deviation occurs when light of one of the following colours passes through a prism (1) Indigo () Green () Red (4) Yellow 8. A ray of light from a sodium lamp undergoes total internal reflection. The critical angle will be smallest when it travels from (1) water to glass () glass to air () glass to water (4) water to air 9. Total internal reflection occurs when light travels from (1) a medium of high refractive index of a medium of low refractive index () a medium of low refractive index to a medium to high refractive index

() a crystalline material to a glass (4) air into water 40. The critical angle of light passing from glass to air is minimum for (1) Red () Green () Yellow (4) Violet