Download Ch. 19 - Optics 19.1 MIRRORS Light is made up of rays that travel in

Ch. 19 - Optics
19.1 MIRRORS
Light is made up of rays that travel in straight lines.
ray diagram --> shows how rays change direction when they strike
mirrors and pass through lenses.
The diagram above shows the law of reflection.
v Incident ray--> the incoming ray; it approaches the
mirror
v Angle of Incidence --> is the angle of the light rays
striking the surface
v
Reflected ray --> the ray leaving the mirror
v Angle of Reflection --> the angle of the light rays
reflecting off the surface.
The law of reflection states that the angle of reflection is equal to
the angle of incidence.
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19.2 LENSES
Light waves bend, or refract, when they pass from one medium to
another because the speed of light changes in each medium.
When light enters a new medium at an angle, the change in speed
causes the light to bend, or refract.
How much the speed of light rays slows as it enters a new material
depends on the material‛s index of refraction - a measure of how
much light changes speed as it enters a new medium. It is calculated
by finding the ratio of the speed of light in a vacuum to the speed of
light in a material.
For example, the speed of light in water is 2.25 x 108 m/s, so the
index of refraction would be 3.0 x 108 m/s divided by 2.25 x 108 m/s
or 1.33.
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When light moves from a material in which its speed is higher (low
index of refraction) to a material in which its speed is lower (high
index of refraction), the ray is bent toward the normal.
If light moves from a material in which its speed is lower (high index
of refraction) to one in which its speed is higher (low index of
refraction), the ray is bent away from the normal.
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Total Internal Reflection
Critical angle --> is the angle of incidence that produces an angle of
refraction of 90 degrees; at the critical angle, light bends so much
that it takes a path along the glass-air boundary.
Total internal reflection --> At angles larger than the critical angle,
the light ray bends so much that it is reflected back into the glass; is
the complete reflection of the light ray back into its original medium.
Materials that have small critical angles are likely to cause most of
the light entering them to be totally internally reflected.
In fiber optics, the principle of total internal reflection is used.
Certain materials such as diamond and glass used in fiber optics have
very small critical angles which causes most of the light entering
these substances to be totally internally reflected.
By making use of total internal reflection, fiber optics are able to
transmit data in the form of light pulses over large distances with
little loss in signal strength.
Read pp. 586-587 on fiber optics.
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