CLASS 8 LIGHT ENERGY

1. Define Refraction Of Light
2. Discussion on Examples Of Refraction
3. Describe the action of CONVEX and CONCAVE mirror
4. Define the terms related to SPHERICAL mirrors
5. Describes the rules for making ray diagrams for SPHERICAL mirror
6. Distinguish between REAL and VIRTUAL image
7. Image formation using CONCAVE and CONVEX mirror.
8. Refraction Prisms: Dispersion Of Light
9. Uses Of CONCAVE and CONVEX mirror

1. WELCOME TO MY CLASS Mr.Souvik Chatterjee M.Sc (Physics), B.Ed

2. LIGHT ENERGY

3. SPEED IN DIFFERENT MEDIA A medium is said to be denser if the speed of light in it decreases, while it is said to be rarer if the speed of light in it increases. If no medium, it can be more than 3 X 10^8 m/s Speed of light in air is 3 X 10^8 m/s Speed of light in water is 2.25 X 10^8 m/s Speed of light in glass is 2 X 10^8 m/s

4. REFRACTION OF LIGHT The change in direction of path of light when it passes from one optically transparent medium to another, is called refraction of light.

5. When ray of light travels from rarer to denser medium, (say from air to water or from air to glass), it bends towards the normal

6. When a ray of light travels from denser to a rarer medium(say, from water to air or from glass to air), it bends away from the normal

7. When a ray of light falls normally on the surface separating the two media, it passes undeviated i.e along the same path

8. SOME TERMS RELATED TO REFRACTION OF LIGHT Incident Ray: The ray of light falling on the surface separating the two media, is called incident ray. Refracted Ray: The ray of light travelling in the other medium in the changed direction, is called refracted ray. Normal: The perpendicular drawn on the surface separating two media, at the point where the incident ray strikes it i.e at the point of incidence, is called the normal.

9. Angle of incidence: The angle between the incident ray and the normal is called the angle of incidence. Angle of refraction: The angle between the refracted ray and the normal is called the angle of refraction.

10. SNELL’S LAW 1. The incident ray, normal at the point of incidence and refracted ray, all lie in a same plane. 2. For a given pair of media and given colour of light, the ratio of the sine of angle of incidence i to the sine of angle of refraction r is a constant i.e Sin i / Sinr =Constant This constant is known as refractive index of the second medium with respect to the first medium.

11. EFFECTS OF REFRACTION

12. APPARENT DEPTH

13. EARLY SUNRISE AND LATE SUNSET

14. MIRAGE

15. REFRACTION IN RECTANGULAR GLASS SLAB

16. DISPERSION OF LIGHT

17. REFRACTION OF LIGHT

18. EXPLANATION OF DISPERSION The speed of light of all colours is same in air or vacuum, but it differs in transparent medium such as glass or water In transparent medium the speed of violet light is minimum and and of red light is maximum. The refractive index of a medium is maximum for violet light and minimum for red light. Therefore, when white light enters a prism, it splits into its constituent colours while refraction at the first surface of the prism

19. KEY POINTS In rainy season, sometimes after rain, we see rainbow in the sky, just opposite to the sun. It is due to dispesion of white light of sun by the rain drops which behaves like small prisms.

20. SPHERICAL MIRROR

21. TERMS/DEFINITIONS

22. PRINCIPAL FOCUS & FOCAL LENGTH

23. RULES TO DRAW DIAGRAMS

24. IMAGE FORMATION BY CONCAVE MIRROR

25. OBJECT IN BETWEEN INFINITY & CENTRE OF CURVATURE (C or 2F)

26. OBJECT IS PLACED AT CENTRE OF CURVATURE(C or 2F)

27. OBJECT IN BETWEEN FOCUS & CENTRE OF CURVATURE (C or 2F)

28. OBJECT IS PLACED AT FOCUS(2F )

29. OBJECT IN BETWEEN POLE & FOCUS (F )

30. IMAGE FORMATION BY CONVEX MIRROR

31. OBJECT IN BETWEEN INFINITY & POLE)

32. USES OF CONVEX MIRROR

33. USES OF CONCAVE MIRROR