CBSE Class 12 Physics Optics Objective Questions

CBSE Class 12 Physics Optics Objective Questions. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

1. A beam of light is coverging towards a point on the screen. If a plane parallel plate of glass of refractive index μ and thickness t is introduced in the path of the beam, the covergent point is shifted

(a) t[ 1-1/μ] away  (b)  t[ 1+1/μ] nearer (c) t[ 1+1/μ] away (d) t[ 1-1/μ] nearer

2. A ray of light from a denser medium strikes a rarer medium at ∠i. The reflected and refracted rays make an angle of 90º with each other. The angle of reflection and refraction are r and r′ respectively. The critical angle is
(a) sin^–1 (tan r) (b) sin^–1 (tan i) (c) sin^–1 (tan r′) (d) tan^–1(sin i)

3. A lens behaves as a converging lens in air and diverging lens in water. The refractive index of material is
(a) equal to 1 (b) between 1 and 1.33 (c) 1.33 (d) > 1.33

4. A point source of light is placed at the bottom of a vessel containing a liquid of refractive index 5/3. A person is viewing the source from above the surface. There is an opaque disc of radius 1 cm floating on the surface. The centre of the disc lies vertically above the source. The liquid from the vessel is gradually drained out through a tap. The maximum height of the liquid for which the source cannot be seen at all from above is
(a) 3/2 cm (b) 4/3  cm (c) 2/3 cm (d) 3/4 cm

5. A glass cube of each side 4 cm and μ equal to 1.5 has a point object at its centre. The circular area which should be covered on each face of the cube to prevent the spot from being observed from any direction for viewing is
(a) 2.51 cm² (b) 5.02 cm² (c) 10.04 cm² (d) 20.08 cm²

6. An object is placed 20 cm in front of a block of glass 10 cm thick having its farther end silvered. The image is formed 33.2 cm behind the silvered surface. The refractive index of glass is
(a) 1.41 (b) 1.46 (c) 1.16 (d) 1.61

7. An air bubble inside a glass slab of refractive index 1.5 appears to be 6 cm deep when viewed from one side and 4 cm deep when viewed from the other side. The thickness of slab is
(a) 10 cm (b) 6.67 cm (c) 9 cm (d) 15 cm

8. A ray of light is incident at one face of an equilateral prism of μ equal to 1.5. If the ray after refraction through the prism, travels along the grazing angle at the opposite face, the angle of incident ray, is
(a) 18.2º (b) 36.4º (c) 27.9º (d) 29.3º

9. A prism has two acute angles of 30º each and refractive index of 1.5. If two parallel light rays AB and CD are incident as shown in the figure, the angle between the emergent rays is sin^–1 (0.75) = 48.6º.

(a) 18.6° (b) 37.2º (c) 48.6º (d) 52º

10. A crown glass prism of 5º has refractive index for violet and red colours as 1.523 and 1.514 respectively. It is combined with a flint glass prism of 4.2º which has got refractive indices of 1.632 and 1.613 for violet and red colours respectively. The flint glass prism is combined with crown glass prism in opposite direction. The net angular dispersion is
(a) 0.124º (b) 0.348º (c) 0.0348º (d) 0.0124º

11. A projector lens of focal length 10 cm magnifies the image of a 2 cm × 2 cm slide on a screen at a distance of 5 m from the lens. The size of the picture on the screen is
(a) 200 cm2 (b) 2401 cm2 (c) 4802 cm2 (d) 9604 cm2

12. A thin prism P1 with angle 4º and made from glass of refractive index 1.54 is combined with another thin prism P2 made of another type of glass of refractive index 1.72 to produce dispersion without deviation. The angle of the prism P2 is
(a) 2.6º (b) 3º (c) 4º (d) 5.33º

13. A ray of light passes from vacuum into a medium of refractive index μ. If the angle of incidence is twice the angle of refraction, then the angle of incidence is
(a) cos^–1 (μ/2) (b) sin^–1 (μ/2)  (c) 2 cos^–1 (μ/2)   (d) 2sin^–1 (μ/2)

14. A ray of light entering a plane surface from air to glass of refractive index 1.5 is partly reflected and partly refracted. If the incident and the reflected lights are at right angles to each other, the angle of refraction is
(a) sin^–1 (√2/3) (b) sin^–1(√2/3) (c) sin^–1(2/√3)    (d) sin^–1(√2/√3) 

15. A concave mirror of 30 cm focal length is used to obtain an image thrice the size of the object. The object should be placed in front of concave mirror at a distance of
(a) 10 cm (b) 20 cm (c) 30 cm (d) 40 cm

16. A concave mirror of focal length f produces an image m times the linear size of object. If the image formed is real, the distance of object from the mirror is
(a) m−1/f (b) (m−1)f/m  (c) (m+1) f/m  (d) (m +1) f

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