rectilinear propagation of light

light is a form of energy. it is an electromagnetic radiation which can travel through a vacuum with a speed of 30,00,000 m/s . We can only see object when it scatters or reflect the light falling on it.

light sometimes act like particle and sometimes like wave.

How is light  formed?-

when  the electron gains energy, it moves to a higher energy level, then drops back to the ground state releasing its excess energy as light.

                                                                 

           in above diagram photon is light                    

 Rectilinear propagation of light -

      light travels in a straight line as long as it is travelling in the same  medium . 

     

To prove that light travels in a straight line -

      THINGS REQUIRED-

     You will need-

      - a candle

      - matches 

      - three sheets of paper.

        Method

1. Make a small hole in the middle of each of the three sheets of paper.
2. Light the candle.
3. Look at the burning candle through the hole in the first sheet of paper.
4. Place the second sheet of paper between you and the candle so that you can still see the candle through the holes.
5. Now do the same with the third sheet so that you can still see the candle. The sheets of paper must not touch each other.
    You will notice that the holes in the paper need to be in a straight line. 
6. now move the middle sheet a little .Then you will see that the light do not passes through the last sheet and this shows that light travels in a straight line and do not bends .

1. Effects of rectilinear propagation of light -

1. Formation of shadow
2. Formation of eclipse
3. Formation of images

     
 Formation of shadows-

         

light travels in a straight line. Now , if an opaque object is placed in front of the light source a black patch is formed behind the object as that is the area where no light can reach .







THE FORMATION OF THE SHADOW DETERMINES IN TWO FACTORS -
1. How large is the object


2. how large is the light source.



Formation of eclipse

an obscuring of the light from one celestial body by the passage of another between it and the observer or between it and its source of illumination.

There are 2 types of an eclipse-

1. Lunar eclipse - 

   A lunar eclipse occurs when the Moon passes directly  behind the Earth into its umbra .  This can occur only when the sun, Earth and moon are aligned exactly, or very closely so, with the Earth in the middle.

2.Solar eclipse-
    As seen from the Earth, a solar eclipse is a type of eclipse that occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks ("occults") the Sun. This can happen only at new moon, when the Sun and the Moon are in conjunction as seen from Earth in an alignment referred to as syzygy.
  

Formation of images

the principal difference between the lens of the eye and an ordinary optical lens is that the former is flexible. The radius of the curvature of the anterior surface of the lens is greater than the radius of its posterior surface. The shape of the lens is controlled by tension in the fibers of the ciliary body. To focus on distant objects, the controlling muscles cause the lens to be relatively flattened. Similarly, these muscles allow the lens to become thicker in order to focus on objects near the eye.

REFRACTION OF LIGHT

so what is refraction?

- refraction is the phenomena when a ray of  light or any wave like radio waves passes through a medium that causes it to bend and so change its direction from its original direction.

AND the refraction of light is just when a ray of light passes through a medium to another  which causes it to change its  direction from its original direction.

Now we know that light can behave like waves sometimes

https://www.youtube.com/watch?v=J1yIApZtLos

you can find all about light #1 at the following blog -

https://lightyearssite.wordpress.com/