LIGHT, Class X, Part 1

                                    TOPICS  

1. Introduction.

2. Properties of light.

3. Reflection.

  -Laws of reflection. 

  -Virtual and real image.                                                                               

4. Image formed by a plane mirror.

 -Characteristics of the image formed by a plane mirror. 

   -Lateral inversion and its application. 

5. Spherical mirrors.  

   -Properties of a concave mirror. 

   -Properties of a convex mirror.

    -A common term for spherical mirrors.                                                 

6. Rules for making ray diagrams by spherical mirrors.

7. Ray diagrams for images formed by a concave mirror.

  -When an object is at infinity. 

  -When an object is beyond C.

  -When an object is at C. 

  -When an object is placed between F and C.

  -When an object is placed at F.

   -When an object is between P and F.

8. Uses of a concave mirror. 

9. Ray diagram of the image formed by the convex mirror.

  -When an object is placed at infinity.

 -When an object is placed between pole and infinity.

10. Uses of a convex mirror.

11. Sign convention for reflection by a spherical mirror.

12. Mirror formulas. 

   -Magnification of a spherical mirror.

                                                                   INTRODUCTION  



Light is the form of energy that provides a sensation of vision.

 Light is needed to see things around us.


 


Image formation by mirrors the twinkling of stars, the beautiful color of a rainbow, bending of light by a medium, and so on. And it is light that makes us see our image in a looking mirror. We detect with our eyes.

We also need a source of light to make objects visible. It is only when light coming from an object enters our eyes that we are able to see that object. This light may have been emitted by the object itself or it may have been reflected by the object.                                                                                                                                                                                     

                                          PROPERTIES OF LIGHT


Light enables us to see objects from which it comes or from which it is reflected. For example, the sum gives out light. We can see because the light coming from the sun enters our eyes. The object which emits its own light is known as a luminous object.



Sun, other stars, electric bulbs, tube light, torch, candles, and fire, etc. Though luminous objects are very small in number but they help us to see a very large variety of non-luminous objects around us.


The object like a flower, a chair or a table do not have the light of their own but even then we are able to see them. Though objects like a flower, a chair or a table, bricks, etc do not emit light, we can see them by the light which they reflect or scatter by taking it from a luminous object.

Those objects which do not emit light by their own but only reflect or scatter the light which falls on them are called non-luminous objects.

          A flower, chair, table, book, trees, other planets, human being fan, bad, mirror, diamond, wall, floor, and Road, etc., are non luminous object in fact most of the object around us are non-luminous objects. 


 

We can see the non-luminous object because they received light from the luminous object and reflect the light into our eyes. So we can say that light is a form of energy that causes a sensation of sight.

  Nature of light

There are two theories about the nature of light; wave theory of light and particle theory of light. Some of the phenomena of light can be explained only if the light is considered to be made up of waves. Whereas others can be explained only if the light is made up of particles.


According to Wave theory, light consists of electromagnetic waves which do not require a material medium for example solid liquid or gas for their propagation. The wavelength of visible light waves is very small. The speed of a light wave is very high it is about 3 × 108 meter per second in a vacuum.



 According to particle, theory light is composed of particles that travel in a straight line at very Speed. The elementary particle that defines light is a Photon.

For example,

1.Diffraction bending of light.



2. Interference



3. Polarization of light


the phenomena of diffraction bending of light around the corners of a tiny object, Interference, Polarization of light can only be explained if the light is considered to be the wave nature. The particle theory of light cannot explain these phenomena.

On the other hand the phenomena of refraction and reflection of light and casting of Shadow of the object by light can be explained only if the light is thought to be made of particle.


 Wave theory of light cannot explain this phenomenon. Thus, there is evidence for the wave nature of light as well as for the particle nature of light.

Physics experiments over the past hundreds of years or so have demonstrated that light is a dual nature of light exhibits the property of both web and particle depending on the situation is in. The modern theory of light called the Quantum theory of light combines both wave and particle models of light.






 









 










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