Post on 26-May-2015
transcript
Light Something that makes vision possibleelectromagnetic radiation of any wavelength that
travels in a vacuum with a speed of about 186,281 miles (300,000 kilometers) per second
Light travels almost a million times faster than sound.
Where does light come from?Luminous Objects — emit light from within Illuminated Objects — reflect externally supplied light
The starsThe sun
The moon Electric lightsFires and flames
Properties & Sources of LightLight travels almost unimaginably fast and far.Light carries energy and information.Light bounces and bends when it comes in contact
with objects. Light has color.Light has different intensities, it can be bright or dim.
Light carries Energy & PowerLight is a form of energy that travels.The intensity of light is the amount of energy per
second falling on a surface.Most light sources distribute their light equally in all
directions, making a spherical pattern.Because light spreads out in a sphere, the intensity
decreases the farther you get from the source.
Light carries InformationThe fiber-optic networks you read about are
pipelines for information carried by light.
Light IntensityThe intensity of light from a small source follows
an inverse square law because its intensity diminishes as the square of the distance.
air
glass
Refraction is the bending of light When the light passes from one medium to another.
Refraction of Light
Reflection of Light
Bending or change in direction of a light beam that occurs at the surface of a substance or object.
air
glass
normal
incident ray
angle of refraction
angle of incidence
refracted ray
Reflection of light
Law of Reflection
The angle of incidence equals the angle of reflection.
The incident ray strikes the mirror.
The reflected ray bounces off.
RefractionLight rays may bend as
they cross a boundary from one material to another, like from air to water.
This bending of light rays is known as refraction.
The light rays from the straw are refracted (or bent) when they cross from water back into air before reaching your eyes.
sin i is directly proportional to sin r.
sin i
sin rO
Relation between angle of incidence and angle of refraction
i = angle of incidence
r = angle of refraction
straight line passing through the origin
Refraction
off a smooth surface (i.e. mirror)
off a rough surface (i.e. white paper)
Seculars Reflection
Diffuse Reflection
Reflection of Light
How does Light travel?
Light rays travel in straight lines from the light source.When it hits an opaque object, some light is absorbed
and the rest reflects off.If the object is transparent, light rays pass through it
easily.If the object is translucent, some light can pass
through, but the rest of the light will be reflected.
lightsource
Color and Vision When all the colors of the rainbow are combined, we
do not see any particular color. We see light without any color. We call this combination of all the colors of light
"white light".
We can think of different colors of light like balls with different kinetic energies.
Blue light has a higher energy than green light, like the balls that make it into the top window.
Red light has the lowest energy, like the balls that can only make it to the lowest window.
Color & Vision
Dispersion and Prisms
When white light passes through a glass prism, blue is bent more than red.
Colors between blue and red are bent proportional to their position in the spectrum.
Dispersion and PrismsThe variation in refractive
index with color is called dispersion.
A rainbow is an example of dispersion in nature.
Tiny rain droplets act as prisms separating the colors in the white light rays from the sun.
How the human eye sees color The retina in the back of the eye
contains photoreceptors. These receptors release chemical
signals. Chemical signals travel to the brain
along the optic nerve.
optic nerve
Which chemical signal gets sent depends on how much energy the light has.
If the brain gets a signal from ONLY green cones, we see green.
The End
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