Deflection of light beam that propagates from one medium to another medium of different optical densities called refraction (refraction) . Refraction occurs because the optical density of the two different mediums . Optical density of the air is smaller than the optical density of the glass so that the refraction of light from air into glass ( glass ) is as shown below II.2 :
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| Figure II.2 process of the refraction of light from air into glass |
Refraction events often encountered in everyday life. If a pencil is inserted into the water with oblique direction until half submerged, the pencil looks as if broken. Sightings as it happens because light reflected from the eye pencil that reaches past the two media : water and air . When light enters the boundary between water and air, changing direction of the beam. This is due to the optical density of the two different mediums. Medium water is denser than air medium .
Like the light reflection, refraction of light also follow certain rules. There are two rules that determine the course of the refraction of light, namely :
a. Law of refraction , which reads light I come , refracted ray and the normal line lies in a plane , all three intersect at one point .
b . The second law of refraction , which reads :
i . Light coming from a less dense medium to a more dense medium is refracted normal line approach .
ii . Light coming from a more dense medium to a less dense medium is refracted away from the normal line .
This rule was first proposed by van Royen Willebrord Snell (1591 - 1626) , a Dutch mathematician , then this rule is also called Snell's law .
Optical density of a medium is expressed by a quantity called the refractive index . Vacuum has the smallest density so that the experts agree that the refractive index of a vacuum rated 1 . Because air density approaching the density of a vacuum , the refractive index of air was considered equal to 1 . By analyzing the refraction of light that comes from the air into a medium , it can be determined from the refractive index of the medium .
Like the sound , the speed of light in the medium range is not the same . On a less dense medium light propagates faster . In contrast , in the more dense medium light propagates slower . This is evident because the light propagates fastest in a vacuum .
A Dutch scientist , Christian Huygens (1629 - 1695) stated that the actual refraction occurs due to differences in the speed of light . According to Huygens , two different media with refractive indices n1 and n2 and the speed of light in it v1 and v2 effect relationship :
n1 v2
=
n2 v1
n1 , n2 = refractive index of the first and second substances
v1 , v2 = velocity of light in the substance first and second ( m / s , cm / s )
If the vacuum is taken as one of the medium, then n1 = 1 and v1 = 3 x 108 m / s . Suppose the medium refractive index n and the second is called the propagation of light in it is v , then we obtain the equation :
c
n =
v
n = refractive index of substances
c = velocity of light in vacuum
v = velocity of light in the substance
Refractive index for some substances can be seen in the table below .
Table II.1 refractive index for several substances
The refractive index of a substance name
Air (0 ° C , 1 atm ) 1.00039
Hydrogen (0 ° C , 1 atm ) 1.00013
Carbon dioxide (0 ° C , 1 atm ) 1.00045
Air 1.33
ice 1.31
ethanol 1.36
benzene 1.50
glycerin 1.48
Canada balsam 1.50
Carbon sulfide 1.62
Quartz glass 1.45
Glass corona 1.53
Glass flinta 1.58
diamond 2.42
If the light comes from a dense medium towards the less dense medium , the angle of refraction is greater than the angle of incidence . If the incident angle is being enlarged , then the angle of refraction was greater . At some point there will come a corner cause bias precise angle 90o . Angle causes worth 90o angle of refraction is called the critical angle . When there is a critical angle , the light is no longer refracted but reflected entirely . Events in the field of the incident light is reflected entirely limit is called total reflection or total reflection .
Actual light that comes on the boundary two different mediums always having reflectivity , although only a small part . Most of the refracted light will come . However , when there is total reflection will come across the reflected beam .
Total reflection can not occur when light moves from less dense medium to a more dense medium . Total reflection occurs only if the angle of refraction is greater than the angle of incidence . This only happens when light propagates from a dense medium towards the less dense medium . Thus , the total reflection condition is as follows :
- Light coming from a more dense medium to a less dense medium .
- Angle of incidence is smaller than the angle of refraction .
If the relative refractive index of the second medium is known , then the critical angle can be determined using projection . Because the refracted ray angle coincides with the limit , then the projection of the same length as the bias light refracted ray itself.
Example of total reflection that occurs is :
a. Mirage .
In hot desert areas , people often see in front of him there was water and shade trees . Once approached , were not found anything . This event is called a mirage . The process of mirage is as follows :
During the day the sand experiencing high heating . Air layer around sand has a higher temperature than the air layer above it . Getting to the top of the lower temperatures . The air has a higher temperature has a lower refractive index . Thus , the air above the sand can be divided into layers with different indices . Lowermost layer of air has a refractive index of the smallest . Getting to the top , the greater the refractive index of air .
Light of trees sloping downward direction will be refracted away from the normal when it enters the air layer underneath. Further down , the greater the angle of refraction of light . On a particular layer , the light is not refracted but reflected perfectly again . This happens because of the angle of incidence of the previous medium beyond the critical angle . Once reflected , light moves from a medium with a small refractive index toward a medium with a refractive index greater. As a result , light is refracted close to the normal line . Light into a curved trajectory . Propagation direction of light entering the eye to cause the person to see the shadow of a nearby tree .
b . Optical fiber .
Fiber optics used in telecommunications as a medium of information delivery . Different fiber optic cables are also a common medium of information delivery . Information sent shockwaves through the cord -shaped , whereas the information is transmitted over optical fiber wave-shaped light . The use of light waves enables the delivery of information much faster than using electric waves . In addition , the use of optical fiber is cheaper and safer . The fiber optic cable can replace dozens at once .
