Light Review
Light is an electromagnetic (EM) wave.
 EM waves are transverse waves.
 No medium is required to travel, but can travel through a medium. Slower in denser medium.
 Speed of all EM waves is 300,000,000 m/s (about 800,000 times faster than sound!)
 At the speed of light, it takes eight minutes for light from the sun to reach Earth.
 Visible light (white light that we can see) is a very small part of the EM spectrum
 All EM waves have different frequencies and wavelengths, but same speed in vacuum.
 Longest wavelength to shortest wavelength are: Radio waves, Microwaves, Infrared, Visible
Light, Ultraviolet, X-ray, Gamma, and Cosmic
Law of Reflection states the angle of incidence is equal to the angle of reflection:
Reflection is the bouncing back of a wave as it hits an object or barrier
o Regular reflection occurs when the light waves hit a smooth surface (clear image)
o Diffuse reflection occurs when the surface is rough (light scatters)
Refraction is the bending of waves as they change mediums. It is caused by the change speeds as EM
waves enter different mediums of different densities.
Diffraction is the bending of waves through an opening or around an object. Causes blurry edges on
shadows.
Light can be either absorbed, transmitted (pass through), or reflected off object.
Depending on their ability to transmit light, objects are classified as:
Opaque- no light is transmitted
Translucent- light passes through, but is scattered, so you cannot see clearly
Transparent- light passes through and objects can be seen clearly
Colors of the rainbow (ROY G BIV) are different wavelengths and frequencies of the visible light
spectrum.
Rainbows can be formed by bending white light through a prism.
The primary colors of light are red, blue and green.
Colors of opaque objects are determined by the color of the light they reflect.
Colors of transparent and translucent objects are determined by the color of light they transmit.
All other colors are absorbed.
Mirrors can be plane, convex, or concave.
o Plane mirrors produce virtual images that are the same size, but reversed left to right.
o Concave mirrors produce real images (beyond the focal point) and virtual images.
o Convex mirrors produce only virtual images.
Lenses are transparent material that bend (refract) light
concave lens (like inside of
spoon)
Definition: A lens that is thicker along the edges than in the middle.
Context: Rays of light that pass through a concave lens
diverge or separate.
convex lens (bulge
outward)
Definition: A lens that is thicker in the middle than on the edges
Context: Convex lenses bend rays of light so that they come together or converge at a focal point.
Magnifying glass is convex lens.
Structure of the Eye
Cornea- clear outer covering, refracts light into pupil
Iris- colored portion, muscles that opens and closes to let light into pupil
Pupil- opening (hole) through which light passes
Lens- refracts light to focus,
Ciliary muscles- change the shape of lens in order to focus close up or far away.
Retina- back of eye that contains sensors
Rods- sensors that detect amount of light
Cones- sensors that detect color. 3 types, red, blue and green
Retina contains the Rods and
Cones.
Vocabulary
illuminated
Definition: Does not generate its own light, but is visible because it reflects light.
Context: The moon is illuminated by the sun’s light.
incandescent
Definition: Light produced by hot objects.
Context: Most light bulbs produce incandescent light.
lens
Definition: A transparent piece of glass or plastic with a curved surface that bends light; a component of the
eye which works in concert with the cornea to refracts light and focus it onto the retina
Context: By changing the curvature of the eye’s lens, one can focus the eye on objects at different distances
from it.
luminous
Definition: produce their own light (light source)
Context: Though the moon appears luminous, its light is actually reflected sunlight.
opaque
Definition: Impenetrable by light; neither transparent nor translucent
Context: When light hits an opaque object, it bounces back.
photon
Definition: A tiny “packet” of energy that is released by an electron that moves to a lower energy level
(shell) in an atom.
Context: The movement of electrons back and forth creates streams of photons.
prism
Definition: A piece of glass or other transparent material whose ends are equal and parallel triangles
Context: Prisms refract white light into the colors of the spectrum.
rays
Definition: Thin lines of light
Context: Rays of light pass easily through transparent materials such as air, glass, or water.
reflection
Definition: The bouncing of light off a surface that it strikes
Context: A mirror image is produced by reflection of light off a smooth surface.
refraction
Definition: The bending of light, occurring when light travels from one transparent material to another
Context: Refraction will cause a spoon that has been placed in a clear glass of water to appear bent.
shadow
Definition: An unilluminated area
Context: Shadows are created by the absence of light.
transparent
Definition: Transmitting light; able to be seen through with clarity (clear)
Context: Light can bend when it goes from one kind of transparent material to another.
white light
Definition: Light that comes from the sun or from an ordinary lightbulb
Context: White light is a mixture of every color of the rainbow (red, orange, yellow, green, blue, indigo,
and violet)