| |
 |
 |
| As light travels from air to water it is
bent towards the normal line, i.e. the angle of incidence is greater than the angle of refraction. |
This also occurs in the formation of a rainbow. The normal line it perpendicualr to the tangent at the point where the light hits the surface of the raindrop. |
 |
 |
| As light travels from air to water it is
bent towards the normal line, i.e. the angle of incidence is less than the angle of refraction. |
When light travels back out of the raindrop, the same thing occurs.
The diagram above shows the angles for
the violet ray. |
In 1621 Willebrord Snell, a Dutchman, found that when the sin of the angle of incidence is divided by the sin of the angle of refraction, the result is a constant value for a given interface (boundary layer between specific materials). This constant number was named the Relative Refractive Index and is specific for each pair of media. For an air-to-water interface, the relative refractive index is 1.33.
A more useful quantity is the Absolute Refractive Index. This
is the relatve refractive index for a vacuum-to-medium interface and is
specific for each medium. Some examples are: Rock salt = 1.54,
Diamond = 2.42, Ethyl Alcohol = 1.36.
(Figures quoted from Eddy De Jong, 1991. Physics One,
Heinemannn Australia.)
)
as Snell's Law. See below.
 |
Where:
|
i is the angle of incidence
r is the angle of refraction n* is the relative refractive index for the 2 media involved |
(i = 40, n* = 1.33) Rearrange equation to get r on its own. Turn both sides upside down to get rid of the reciprocal Find sin 40 and calculate the value of sin r Use the inverse sin button on your calculator to find the value for r. |
 |