Ray Optics and Optical Instruments Mock Test – Class 12 Physics

1. Assertion: Interchanging and in the spherical refracting surface formula generally changes the result.
Reason: and represent the incident and refracted media, so their placement carries the direction of light crossing the surface.

2. In refraction from air into glass at a convex spherical surface of radius , a real object is placed in front of the surface. The image distance is

3. Two convex lenses and have focal lengths and , respectively. If both receive parallel rays from a distant object, the correct comparison is

4. Assertion: A compound microscope uses a short focal length objective.
Reason: A smaller increases the objective magnification factor in the approximate expression .

5. A telescope in normal adjustment gives an inverted final image. This happens mainly because

6. For a prism with and , the refractive index is

7. The critical angle for a denser-rarer pair is the angle of incidence in the denser medium for which

8. In a convex mirror construction, a ray directed toward the centre of curvature behind the mirror is reflected back

9. A concave mirror faces an object placed in front of it. The incident light travels from left to right, and the pole of the mirror is at the origin. The object distance is taken as negative because the object is

10. A thin lens is described as having negligible thickness compared with its focal length and object distance. This approximation is useful because

11. A ray crosses from medium to medium without any change in direction even though it meets the boundary obliquely. The best conclusion is that

12. The following comparisons are made for optical fibres:

The correct rows are

13. When an object moves from a very large distance toward a convex mirror, the image

14. A mirror has , and a virtual image is formed behind the mirror. The object distance is

15. A student says, “A swimming pool looks shallow because water absorbs some light from the bottom.” The better explanation is that

16. An astronomical telescope has and . In normal adjustment, its magnifying power and tube length are

17. For a thin concave lens in air receiving light from left to right, the focal length is negative because

18. A graph is described for a convex mirror with object distance magnitude increasing along the horizontal axis and image distance behind the mirror along the vertical axis. As the object becomes very far away, the image position approaches

19. A narrow beam of white light passes through a prism and forms a spectrum on a screen. The violet end is more deviated than the red end because

20. For a real object placed anywhere in front of a convex mirror, the image is formed

21. If water droplets did not disperse sunlight but still refracted and internally reflected it, the observer would mainly see

22. An astronomical telescope has magnifying power in normal adjustment. If the eyepiece focal length is , the objective focal length should be

23. Assertion: The sky appears blue mainly because blue light is scattered more than red light by air molecules.
Reason: For Rayleigh scattering, , so shorter wavelengths scatter more strongly.

24. A glass plate appears to have a smaller thickness when viewed normally from above. If its actual thickness is and refractive index is , the apparent thickness is

25. An optical device is useful in ray optics when its action can be understood by following the change in direction of light rays. A suitable example is

26. For a normal human eye, the least distance of distinct vision is usually taken as

27. A concave mirror of focal length forms a real image of a tall object with magnification . The object distance and image distance are respectively

28. A slab has actual thickness . When viewed normally from air, its apparent thickness is . The apparent shift and refractive index are respectively

29. The lens maker's formula for a thin lens in air relates the focal length mainly to

30. At minimum deviation in a prism, the path of the ray inside the prism is symmetrical. This means

31. A concave lens is used in spectacles for a person whose eye needs incident rays to be spread out before entering the eye. The lens is chosen because it

32. In a prism ray diagram, the angle of deviation is measured between

33. An instrument has a short focal length objective, a short focal length eyepiece, and a tube length much larger than both focal lengths. It is most likely a

34. Diffraction limits the resolving power of a telescope because light from a point object forms

35. A result table for refraction at a spherical surface is shown:

The acceptable rows are

36. The real and apparent depths for three liquids are recorded for near-normal viewing from air:

The liquid with the greatest refractive index is

37. Two prism materials are compared:

The material with greater dispersive power is

38. Medium has refractive index , and medium has refractive index . For the same monochromatic light, the speed and wavelength are

39. A table compares atmospheric colour phenomena:

The suitable rows are

40. A convex lens forms a virtual erect image of a real object. The object position is

41. For a simple microscope, the magnifying power when the final image is formed at the near point is

42. A telescope has aperture and uses light of wavelength . Another telescope uses aperture and wavelength . The ratio of their limiting angular separations is

43. A concave mirror forms a real image in front of it when an object is placed in front of the mirror. The focal length of the mirror is

44. A student's slab diagram shows the emergent ray making a smaller angle with the normal than the incident ray, although the slab is in air on both sides. The main error is that the student has ignored

45. A structure-function record for the human eye is given below:

The suitable rows are

46. For a spherical mirror, the radius of curvature is . Under the paraxial approximation, the magnitude of the focal length is

47. A spherical mirror has centre of curvature located in front of its pole . If incident light travels from left to right and the mirror faces the incident light, the sign of is

48. The main difference between magnification and resolution is that magnification describes

49. The optical centre of a thin lens is important because a ray passing through it is usually drawn as

50. An equiconcave lens in air has , , and . Its focal length is