The Bases of the Optics


3. Refraction of the Light:

 (1)Refraction Law of Light ( Snellfs Law):

The sin making with incidence angle ( i ) of light (PO) and perpendicular line (ON) on the incidence point(O) is constantly proportional with the same of refracted angle ( r ) on the same surface.

Sin i / Sin r = n (Constant)

We can realize the phenomena , with the following example, which the light is refracted on the boundary between the different mediums. While you are driving a car and when your car is suddenly running at an angle into snowy area on the road in the winter, the speed of your car is rapidly decreased down because of the great impact against to the front wheel. ( The speed of the refracted light is also decreased.). Your car is inevitably curved to the direction of the front wheel entered into the snow first. Please have an image by interchanging that your car is the light and the road is medium 1 and the snowy area is the medium 2.

(2)Refracted Ratio:

The constant value of g n h under the above calculation formula is called as gRefracted Ratioh of the medium 2 to medium 1. In other words, it is called as the refracted ratio of light when the light is going into the medium 2 from medium 1. Further, it is also understood the refracted ratio is the speed ratio on the medium 1 to medium 2.

The refracted ratio varies depending on the colors of the light and with the temperature

even if the medium is same. The refracted ratio of following mediums are as under:

   Diamond         2.4                          Glass        1.5~1.8      

   Ethyl-alcohol     1.36                         Water        1.33

   Air at 1 air pressure with the temperature at 20o C.     1.00029 (about 1.000)

‚SD The Floating by the refraction:

(1) In case the eyes are in the air:


¦If an one-hundred-Yen coin is at 10cm depth of the water tank with the liquid of 1.45 refracted ratio , it may be appeared that the coin is at about 7cm depth of the water ( 10cm/1.45 = 7cm).

i3jIn case the eyes are in the liquid;

hf = nh

         The coin is appeared higher in the air, in case eyes are in the liquid

5.  Whole Reflection:

When the light goes into from the higher refraction medium to the lower refraction
 one, the angle of incidence of light is always bigger than the angle of the refraction and the angle of incidence is sometime at 90‹.

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@(b) In the air

According to the Reflection Law:                  @@@@@@@@According to the Reflection Law:

‚Ž‚Q‚r‚‰‚ŽƒΖ‚Ž‚P‚r‚‰‚Ž‚X‚O‹@@@@@@@@@@@@@@@@@@‚Ž‚r‚‰‚ŽƒΖ‚P~‚r‚‰‚Ž‚X‚O‹ @@

When the angle of incidence is bigger than ?, no refraction is appeared but only the reflection of the light is observed.  This phenomena of the light is called as the whole reflection and this ? is called as the critical angle of the light.

When whole reflection is appeared:     @@@@@@@@@@@@@@    When whole reflection is appeared:

‚r‚‰‚ŽƒΖ„‚r‚‰‚ŽƒΖ‚Ž‚P^‚Ž‚Q@@@@@@@@@@@@@@@@@@@@‚r‚‰‚ŽƒΖ„‚r‚‰‚ŽƒΖ‚P^‚Ž @@@@@@

The critical angles of light in the air are as under:

    Water ( n = 1.333 ) 49‹@@@@@@@@Glass@( n = 1.5 ) 42‹

@Diamond@(n = 2.42@)@24‹

yThe Reason why the diamond is sparklingz

The cut diamond sparks because of the whole reflection as mentioned above. When
the light goes into the diamond, it is reflected on the many surfaces of the diamond.  @@
This reflection appears till then the angle of incidence (?) of light on the surface
becomes smaller than the critical angle and ,as mentioned in the item of Reflection
Ratio, the light goes out only with losing a little. from the diamond. The sparkling of
the diamond we can see is because of the whole reflection of light on the cut surfaces.

To be continued

Next story will be on the Spectrum of light, the color of light, the color of medium as well as the interface of light. It will be appeared on this HP on November 1, 2002 onwards.@

If you have interest of the first story of this Bases of The Light, please do not hesitate to contact to

VOL.001.The Bases of the Optics