Download 1 Optical Phenomena

Optical Phenomena Date ________
Total Internal Reflection
Light is reflected and refracted when the flashlight is under the water.
The proportion of light refracted and reflected is shown by the different size arrows. When light moves from a material where the speed of light is slower to a material where the speed of light is faster the light bends _____________ from the normal.
As the angle of incidence increases the amount of light refracted decreases.
At the critical angle and above there is total ________________ ___________________.
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Applications for Total Internal Reflection
Prisms can be arranged in optical equipment instead of mirrors to totally reflect light because they are more efficient and more scratch resistant.
Fiber Optics
Total internal reflection is used to
transfer light from one place to another.
It is useful for viewing objects in inaccessible locations in medical
applications.
Fiber optics is used in telecommunications
because the fibers can carry higher
volumes of telephone calls and computer
signals than electrical wires can. 2
Mirages produced by refracted light.
Have you ever seen water on the road on
a hot sunny day? The ground is so hot that the air right above the ground is hotter than the air above it.
The light traveling through the air at different temperatures is bent so it appears to reflect
the blue sky. Light moving through hot air moves ________________ than when it moves through cold air. 3
A mirage can be observed when the ground
is so hot that the air right above the ground
is hotter than the air above it.
Above the ground are layers of air with
different indexes of refraction.
The light from the tree reaches the observer
in a straight line path A.
Other light rays directed toward the ground
are bend because the hot air above the ground
has a lower index of refraction and the light
bend in the curved path B.
The observer traces these light rays back to the point from which they APPEAR to have originated. The observer see an inverted image of the tree.
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Dispersion
The index of refraction for
substance is dependant on the wavelength of the light
going through that substance.
For example, blue light, with a shorter wavelength, bends more than red light when
passing into a refracting material.
The process of separating polychromatic light into its components is called dispersion.
When white light enters a prism, the blue component light is bent more so the light rays that emerge from the second face of the prism fan out into the visible spectrum.
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Rainbows
Rainbows can be seen in the sky, at the base of a waterfall, or near a backyard sprinkler. Bright sunlight, suspended droplets, and a proper angle are all necessary for viewing a rainbow.
To see a rainbow in the sky, your back must be to the sun and you must look upward (about 40 degrees) above the ground. There must be water droplets or a light mist in the atmosphere.
There are many paths for the light rays to pass through the
water droplets in the sky. When the light refracts into the
droplet, internally reflects, and then refracts out of the droplet, the light rays are bent downward towards an observer on the
Earth.
Dispersion occurs when light is separated into its components.
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The half­circle results because there is a collection of suspended droplets in the atmosphere that concentrate the dispersed light from the sun. Each droplet in the arc disperses the light and reflects it back toward the observer.
Each droplet is refracting and dispersing the ENTIRE visible light spectrum. The red light is refracted at steeper angle towards the ground that the blue light. When an observer looks at a steep angle the red light is refracted to the observer's eye and the blue light from the same
droplets is directed over the observers's head. When the observer looks at a less steep angle, the droplets of light refract the blue light to the observer's eye and the red light is directed at a steeper angle towards the observer's feet
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1) What two conditions are necessary for total internal reflection to occur?
Light moves from a material where the speed of light is slower to a material where the speed of light is faster.
The angle of incidence is at or above the critical angle.
2) If the air above the road is hotter than the air above it, why does the light refract to produce a mirage?
The layers of warm air have different indexes of refraction so the light refracts as it goes through each layer.
3) Why do prisms separate out the different colors in white light?
When white light enters a prism the blue light is bent more because it has lower wavelength. When the light exits the prism it bends again. The blue light is bent more again and the visible light spectrum is observed.
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Dispersion
The index of refraction for
substance is dependant on the wavelength of the light
going through that substance.
For example, blue light, with a shorter wavelength, bends more than red light when
passing into a refracting material.
The process of separating polychromatic light into its components is called dispersion.
When white light enters a prism, the blue component light is bent more so the light rays that emerge from the second face of the prism fan out into the visible spectrum.
These colors are in order of decreasing wavelength: red, orange, yellow, green, blue, violet.
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Rainbow are created by dispersion of light
in water droplets.
The observer must be positioned between the
sun and a rain shower.
When a ray of sunlight hits a drop of water,
it is refracted at the front surface of the drop.
The ___________ light refracts the most.
The light is __________ at the back of the water droplet and returns to the front surface.
There the light is ______________ again with the violet light refracting the most.
When an observer see a water droplet high in the sky, the red light reaches the observer, but the violet light passes over the observer because it bend from the white light more than the red light.
So this droplet looks red.
A drop lower in the sky would look violet because that droplet directs the violet light to the observer and the red light from this drop would hit the ground and not be seen,
The remaining colors would reach the observer from the raindrops between the two extreme positions.
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For each combination of media, which light ray (A or B) will undergo total internal reflection if the incident angle is gradually increased
Practice A: Light ray A is in the more dense medium and it will be the one which will undergo TIR.
Practice B: Light ray A is in the more dense medium and it will be the one which will undergo TIR.
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