Light

No. Light       
1. Any substance that allows to transmit through it any form of energy is called medium.
2. Unit of intensity of light is Lumen.
3. If the source of light is taken away the intensity of light decreases.
4. Air is removed and inert gases are filled in an electric bulb.
5. Sun is self luminous body. Planets are non-luminous bodies. They are only reflectors of light.
6. Light travels in straight lines.
7. The substances that allow light to pass through them are called transparent substances. Ex: Glass, Air, Water etc.
8. The substances that do not allow the light to pass through them are called opaque substances. Ex: Wood, Rubber, Stone, Human body etc.
9. Umbra and Penumbra are formed when the object is smaller than the source of light.
10. Eclipses are two types. They are:
11. a) Lunar Eclipse b) Solar Eclipse
2. The Lunar Eclipse takes place on a full moon day.
12. The Solar Eclipse occurs on a new moon day.
13. The phenomenon of causing back of light after hitting a smooth plane is called reflection.
14. Concave mirrors are used in Telescopes.
15. To see patients ear,nose or throat ENT doctor uses concave mirror.
16. Concave mirrors are used in headlights of moter vehicles, tourches etc.
17. Convex mirrors are used in motor vehicles to let the drivers see the vehicles coming from behind.
18. The incident ray, the normal and the reflected ray lie on the same plane. It is called first law of reflection.
19. The incident ray and the reflected ray lie on either side of the normal. This is called second law of reflection.
20. The angle of incidence is equal to the angle of reflection. This is called third law of reflection.
21. If the reflected rays appear to come from a point that point is the virtual image of the object. Plane mirror forms a virtual image.
22. If the reflected rays meet at a point that point is called the real image of the object.
23. Real and virtual images can be seen but only real images can be caught on a screen.
24. Reflection of light is used in Periscope.