Tuesday 4 October 2011

class 10 - Notes on Light and Reflection

Notes on Light and Reflection
1. Light is a form of energy. Since energy cannot be seen, we see objects in light.

2. A ray of light is a straight line which represents the path of traveling light. A collection of light rays is called a beam of light.

3. Q: How do we see objects?
   Ans: The visual ability of humans is the result of the complex interaction of light, eyes and brain. We are able to see because light from an object can move through space and reach our eyes. Once light reaches our eyes, signals are sent to our brain, and our brain deciphers the information in order to detect the appearance, location and movement of the objects we are sighting at.

4. Luminous objects are objects that generate their own light. e.g. firefly, the sun.

5. Illuminated objects are objects that are capable of reflecting light to our eyes. e.g. the moon

6. A ray of light that falls on a surface is called incident ray.

7. The light that is sent back by the reflecting surface is called reflection.

8. The ray that is sent back by the reflecting surface is called the reflected ray.

9. When light falls on a body, it may be absorbed, may be transmitted or light may come back to the same medium.

10. Laws of Reflection (watch  the you tube video):

     a. First law of reflection: The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane.

      b. Second law of reflection: The angle of incidence is equal to the angle of reflection.

11. Real image is obtained when the rays of light after reflection, actually converge at a point. It can be obtained on the screen and can be seen with the eye.

12. Virtual image forms when rays of light do not actually meet, but appear to meet when produced backwards. It cannot be obtained on the screen.

13. Q: Name the characteristics of image formed on plane mirror.
      i) image is virtual and erect.
     ii) size of image is same as the size of the object and laterally inverted.
    iii) distance between image and mirror = distance between object and mirror.

14. Concave mirror: A curved surface whose inner side is capable of reflection.

15. Convex mirror: A curved surface whose outer side is capable of reflection.

16. The radius of curvature of a spherical mirror is twice of its focal length.

17. Mirror Equation is:

18. Magnification: The ratio of the size of the image to the size of the object.

19. Snell's law: n = sin i/ sin r , is a constant. This is the refractive index of the medium.     

20. Presentation on Optics:


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