UNIT.2.OPTICS -FILLUPS

1. Any object which gives out light are termed as source of light.
2. Some of the sources emit their own light and they are called as luminous objects.
3. Examples for luminous objects sun, stars.
4. Light always travels along a straight line.
5. Light does not need any medium for its propagation. It can even travel through vacuum.
6. The speed of light in vacuum or air is,c = 3 × 10⁸ ms^–1.
7. Among the visible light, violet light has the lowest wavelength and red light has the
   highest wavelength.
8. Second law of refraction also known as Snell’s law.
9. When light travels from a denser medium into a rarer medium, the refracted ray is
   bent away from the normal drawn to the interface.
10. When light travels from a rarer medium into a denser medium, the refracted ray
    is bent towards the normal drawn to the interface.
11. Angle of refraction is the smallest for red and the highest for violet.
12. The refractive index of a medium is dependent on the wavelength of the light.
13. Based on initial and final energy of the light beam, scattering can be classified as,
    1) Elastic scattering 2) Inelastic scattering.
14. Rayleigh’s scattering law states that, “The amount of scattering of light is inversely
    proportional to the fourth power of its wavelength”.
15. Rayleigh’s scattering law ‘S’ ∝ 1/ λ⁴.
16. The blue colour (shorter wavelength) is scattered to a greater extent than the red colour (longer wavelength).
17. Mie scattering is responsible for the white appearance of the clouds.
18. The scattering of light rays by the colloidal particles in the colloidal solution is
    called Tyndall Scattering or Tyndall Effect.
19. The spectral lines having frequency equal to the incident ray frequency is called
    ‘Rayleigh line’.
20. The spectral lines which are having frequencies other than the incident ray
    frequency are called ‘Raman lines’.

21. The lines having frequencies lower than the incident frequency is called stokes lines.
22. The lines having frequencies higher than the incident frequency are called Antistokes lines.
23. A lens is an optically transparent medium bounded by two spherical refracting surfaces
    or one plane and one spherical surface.
24. A convex lens is also called as converging lens and a concave lens is also called as diverging lens.
25. Convex lenses are used as camera lenses, magnifying lenses, making microscope,
    telescope and slide projectors, to correct the defect of vision called hypermetropia.
26. Concave lenses are used as eye lens of ‘Galilean Telescope’,
27. Concave lenses are used in wide angle spy hole in doors.
28. Concave lenses  are are used to correct the defect of vision called ‘myopia.
29. Lense formula is 1/ f = 1/v – 1/u.
30. The lens formula relates the focal length of a lens with the distance of object and image.
31. The lens maker’s formula is 1/f = (µ - 1) (1/R1-1/R2 ).
32. Power of a lens is numerically defined as the reciprocal of its focal length.
33. Power of a lens P = 1/f and its unit is diopter.
34. The power of a convex lens is taken as positive whereas the power of a concave lens  is  taken, as negative.            
35. Eye consists of a tough membrane called sclera, which protects the internal parts of the eye.
36. In human eye when light enters through the cornea, it refracts or bends the light on to the lens.
37. Sensitive part of human eye, on which real and inverted image of objects is formed is retina.
38. Ciliary muscles  helps to change the focal length of the eye lens according to the position
    of the object.
39. Eye Lens is convex in nature.
40. The ability of the eye lens to focus nearby as well as the distant objects is called power of
    accommodation of the eye.
41. Power of accommodation of the eye  is achieved by changing the focal length of the eye lens with the help of ciliary muscles.
42. When we see distant objects, the ciliary muscle relaxes and makes the eye lens thinner. This increases the focal length of the eye lens.
43. When we look at a closer object, the focal length of the eye lens is decreased by the
    contraction of ciliary muscle.
44. The minimum distance  Least distance of distinct vision is 25 cm for normal human eye and far point of the eye  is infinity for normal eye.
45. A normal human eye can clearly see all the objects placed between 25cm and infinity.
46. Myopia, also known as short sightedness--lengthening of eye ball--nearby objects can be seen clearly but distant objects cannot be seen clearly ---focal length of eye lens is reduced ----image of distant objects are formed before the retina ----corrected using a concave lens.  (any one point may be asked) (may be used for differentiate question)
47. Hypermeteropia, also known as long sightedness, shortening of eye ball.-- distant objects can be seen clearly but nearby objects cannot be seen clearly.  the focal length of eye lens is increased---the image of nearby objects are formed behind the retina ….corrected using a convex lens. (any one point may be asked) (may be used for differentiate question)
48. Presbyopia is due to ciliary muscles become weak and the eye-lens become rigid         (inflexible).
49. Presbyopia s also called as ‘old age hypermetropia’.-- corrected by ‘bifocal lenses’--upper part consists of concave lens (to correct myopia) --lower part consists of convex lens (to correct hypermetropia).
50. Astigmatism  means eye cannot see parallel and horizontal lines clearly due to the imperfect structure of eye lens -- can be corrected by using cylindrical lenses (Torrid
    lenses).
51. Uses of Simple microscope are  (i) by watch repairers and jewelers (ii) to read small letters clearly (iii) to observe parts of flower, insects etc (iv) to observe finger prints in the field of forensic science.
52. Travelling Microscope’s least count is 0.01 mm.
53. An astronomical telescope is used to view heavenly bodies like stars, planets galaxies and
    satellites.