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When a stick is partialy submerged in the water the part below the
water appears bent because the direction of light, as it passes FROM water
TO air at an angle, is bent toward the water. In Fig.1 below
Fig.1
EYE
* / stick
* /
* /
air * (a) /
--------------------*------------------/--------
water * + //
* + / /
* +/ /
* (2) /
* /
*/ (1)
We see a straight stick partially submerged. A person sees light
from the end of the stick (1) emerging from the water at (a). The light
is bent here so that the ray of light (shown by * * * ...) emerges
from the water less steep than when the ray was in the water. The
EYE of an outside observer then sees the end of the stick at (2) rather
than at (1) so the stick appears bent. The degree to which the light is
bent
as it passes from one medium to another depends on the angle at which
the light strikes the boundary of the two mediums and the speed of light
in the two mediums. the speed of light in a medium is described by a
constant called the index of refraction n.
(1) speed of speed of /
light in = light in / n
a medium vacuum /
For example if the refractive index is 1.33 then the speed of light in the
medium is
3 x 10^8 m/s / 1.33 = 2.26 x 10^8 m/s
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