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| glossary |
| Glossary
of terms:
concave
Bending
inward. A concave lens or mirror has
at least one side that bulges inward.
A concave lens produces diverging light rays.
See also reflect, refract, focal length, focal point
converge
To
move in the same direction or towards
a common point. Light converges
when it passes through a convex lens.
The opposite of converge is
diverge
convex
Bending
outward. A convex lens or mirror has
at least one side that bulges outward.
A convex lens produces converging
light rays. A convex mirror produces
diverging rays.
See also reflect, refract, focal length, focal point
diffraction
A
phenomenon that occurs whenever a
wave is obstructed in any way. Often
diffraction fringes can be seen when
a small aperature or object blocks
light waves. Scientists use diffraction
gratings to break up light into many
wavelengths.
diffraction
grating
A
device used to break light into its
component wavelengths. It is usually composed of a material with
tiny grooves cut into it which disperses the light as it passes through or bounces off
the grating (depending on the type
of grating). Physicists and astronomers
often use diffraction gratings to
study the nature of light.
See also disperson, spectrum
disperse/dispersion
Breaking
light into its various wavelengths.
All transparent materials disperse
light because their refractive indexes change with wavelength: red light (long wavelengths) will be refracted
less than blue light (shorter wavelengths).
diverge
To
move in different directions from
a common point or from each other.
from Webster's New World Dictionary.
The opposite of diverge is converge.
double
concave
A
concave lens which has both edges bulging inward.
double
convex
A
convex lens which has both edges bulging outward.
focal
length
The
distance from a lens or mirror to
its focal point. The focal length, f, is the defining parameter
of most lenses and mirrors.
See also concave, convex
focal
point
The
point at which parallel light rays,
incident on a lens (or mirror), are
focused after refracting (or reflecting). For concave lenses and mirrors, the focal point is on the same
side of the lens (or mirror) as the
source. For convex lenses and mirrors, the focal point is on the opposite
side of the lense (or mirror) as the
source. See also focal length
incident
Falling
or shining upon. When light is incident
on something, the light may be reflected, refracted, absorbed, or any combination of these.
See also total internal reflection
index
of refraction
A
number signifying how well a material
can refract light. Usually specified as n by scientists, the
index of refraction of a material
depends on its composition and density.
Water has an index of refraction of
1.333; n of air is nearly 1.0; and
n of a vacuum is exactly 1.0.
infrared
A
region of the electromagnetic spectrum
that is of lower energy and longer
wavelength than visible light. Typical wavelengths of
infrared radiation range from 1.0
mm to 780 nm (780 x 10-9
m).
interaction
Any
action and reaction that takes place
between two objects. In physics, interactions
(or forces) fall into four main categories.
These categories are gravitational
interactions, electromagnetic interactions
(electric and magnetic forces), and
the strong and weak interactions (which
affect atomic nuclei and fundamental
particles).
interface
The
boundary between two different materials
or media.
See also refraction
interference
The
result of waves impinging on one another.
Constructive interference occurs when
the waves are nearly in phase, or
when their "peaks" combine; destructive
interference occurs when the waves
are nearly 180° out of phase, or when
the "peaks" cancel out the "troughs"of
the waves.
magnify
To
cause an image to appear larger or
smaller than the corresponding object.
When we look through a lens, we often
see things magnified: convex lenses often magnify objects larger, while concave lenses always magnify objects smaller. Mirrors can
also magnify objects.
negative
charge
Something
has a negative charge if it has an
excess number of electrons.
normal
Perpendicular.
If one line is normal to another,
then they are at right angles to each
other.
prism
A
device used to break light into its
component wavelengths. This is usually a triangular piece of glass
through which light can pass and get
dispersed. Isaac Newton first used a prism to see a spectrum
of colors in 1672. See also index of refraction, refract
ray
tracing
A
process used in optics by which the
position and orientation of an image
can be established if one knows the
focal length of the lens and the position of the object.
This process uses strategic rays from
the object passing through the lens
to locate the image. For more detail
- read article on Raytracing.
real
image
A
type of image created by converging light rays. This type of image would
form on the image side of a
lens, where it could be projected.
The opposite of a real image
is a virtual image.
See also convex lens
reflect
When
light bounces off an object. Usually
we associate reflection with a smooth,
polished surface, however the surface
doesn't have to be smooth. Light reflects
off your shirt, therefore others can
see that you're wearing one.
refract
When
light bends at an interface between two transparent materials. We
find many things in our everyday experience
refracting light: glass, water, air,
plastic. The illusion of a broken
leg dangling in the pool is due to
the refraction of light. See also
index of refraction
refractive
index
See
index of refraction
types
of charges
There
are two types of charges: positive
and negative.
ultraviolet
A
region of the electromagnetic spectrum
that is of higher energy and shorter
wavelength than visible light. Typical wavelengths of
ultraviolet radiation range from 375
nm to 12.5 nm (12.5 x 10-9
m).
virtual
image
A
type of image created by diverging light rays. This type of image would form
on the object side of a lens,
if it formed at all. The opposite
of a virtual image is a real image. See also concave lens
wavelength
The
distance from the peak of a wavecrest
to the peak of the subsequent wavecrest,
or from one trough to the next trough.
Expressed in units of distance (e.g.
km, m, cm, micron, nm)
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