Light is electromagnetic radiation that travels at about 300,000 km/s. It can be emitted from luminous objects like stars or reflected from illuminated objects like the moon. Light carries energy and information, travels in straight lines, and can be reflected, refracted, or absorbed when interacting with objects. The human eye detects light via photoreceptors in the retina that send signals to the brain, allowing us to see color.

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2.  Something that makes vision possible
 electromagnetic 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.

3.  Luminous Objects — emit light from within
 Illuminated Objects — reflect externally supplied light
The starsThe sun
The moon Electric lights
Fires and flames

4.  Light 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.

5.  Light 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.
 The fiber-optic networks you read about are pipelines
for information carried by light.

6.  The intensity of light from a small source follows an
inverse square law because its intensity diminishes as
the square of the distance.

7. air
glass
 Refraction is the bending of light
 When the light passes from one
medium to another.
Bending or change in
direction of a light beam
that occurs at the surface
of a substance or object.

8. air
glass
normal
angle of
refraction
angle of incidence

9. The angle of
incidence equals
the angle of
reflection.
The incident ray
strikes the mirror.
The reflected ray
bounces off.

10.  Light 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.

12. sin i is directly proportional to sin r.
sin i
sin r
O
Relation between angle of incidence and angle of refraction
i = angle of incidence
r = angle of refraction
straight line passing through the origin

13. off a smooth surface (i.e. mirror)
off a rough surface (i.e. white paper)
Seculars Reflection
Diffuse Reflection

14. 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.
light
source

15.  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".

17.  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.

18.  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.

19.  The 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.

20.  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.

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