Name _________________________________________________________
5.3 a-e Light
5.3
The student will investigate and understand basic characteristics of visible light and how it
behaves. Key concepts include
a) transverse waves;
b) the visible spectrum;
c) opaque, transparent, and translucent;
d) reflection of light from reflective surfaces; and
e) refraction of light through water and prisms.
Terms you need to know:
Diffraction
Opaque
Reflect
Refract
Telescope
Filament
Transparent
Microscope
Concave lens
Spectroscope
Convex lens
Translucent
Light waves
Electromagnetic spectrum
Light is everywhere in our world. We need it to see: it carries information from the world to our
eyes and brains. Seeing colors and shapes is second nature to us, yet light is a perplexing
phenomenon when we study it more closely.
Waves are a means by which energy travels. Many different particles move in waves. The
waves on an ocean are physical waves caused mainly by wind. Light is an electromagnetic
wave caused by excited electrons.
Light will travel forever unless it hits an object. When it does hit something it will do one of three
things:
1. Reflection is when waves, whether physical or electromagnetic, bounce from a
surface back toward the source. A mirror reflects the image of the observer.
2. Refraction is when waves, whether physical or electromagnetic, are deflected
when the waves go through a substance. The wave generally changes the angle
of its general direction.
3. Absorption is when all the light energy is absorbed
Transverse Waves
Most kinds of waves are transverse waves. In a transverse wave, as
the wave is moving in one direction, it is creating a disturbance in a
different direction.
The electromagnetic spectrum is
more familiar to you than you might
think. The microwave you use to heat
your food and the cell phones you
use are part of the Electromagnetic
Spectrum. The light that our eyes can
see is also part of the electromagnetic
spectrum. This visible part of the
electromagnetic spectrum consists of
the colors that we see in a rainbow from reds and oranges, through blues
and purples.
Light Frequencies
Light waves also come in many
frequencies. The frequency is
the number of waves that pass a
point in space during any time
interval, usually one second.
Color is the thing we perhaps notice most about light
in the world around us. But why we see colors the way
we do all has to do with light. The reason something
appears to be the color that does is that the object is
absorbing all the other colors of light except the ones
we see, which are reflected back to our eyes. If
something absorbs all the colors, it appears black, if it
reflects everything, it appears white. Color comes from
what is called the visible spectrum of light. This
spectrum goes from red to orange to yellow to green to
blue to indigo to violet, all the major colors of the
spectrum, and everything in between. An easy way to
remember this order is to remember Roy G. Biv, much
like the colors of the rainbow. Scientists
measure the wavelengths of light in this
spectrum in nanometers or billionths of a
meter. Red has the longest wavelength,
and violet has the shortest. So, what
color we see depends on the wavelength
of the light we absorb into our eyes. The
primary colors are red, green, and blue,
from these colors, every other color can
be made.
 Visible light is a combination of several different wavelengths of light traveling together.
These wavelengths are represented by the colors red, orange, yellow, green, blue, indigo,
and violet (ROYGBIV).
 Light waves are characterized by their wavelengths. In the visible spectrum, red has the
longest wavelength, and violet has the shortest. Wavelengths get progressively shorter from
red to violet.
 Light travels in waves. Compared to sound, light travels extremely fast. It takes light from
the sun less than 8½ minutes to travel 150 million kilometers to reach the Earth.
Color also varies on the amount of light present in the area, which is why things can appear different in
different light, and with different reflectors around them. A prime example is people with blue eyes,
depending on the clothes they are wearing, the shade of blue in their eyes can lighten or deepen,
depending on which light waves are being reflected by the clothes they are wearing. Outside of the visible
spectrum, there are many non-visible forms of light, infra-red which is used in remote controls, ultraviolet
light, used in black lights, x-rays used in x-ray machines, and gamma rays and other various forms of
radiation given off from the sun.
One of the most important experiments on light was made by Isaac Newton. He was the greatest of all
English men of science. He discovered that sunshine (white light) is made up of many colors. Over 300
years ago, Sir Isaac Newton passed a beam of white light through a prism. A prism is a triangular piece of
glass, which allows light to spread out into a band of six colors. These colors are red, orange, yellow,
green, blue and violet. Newton then sent this light through a second prism where the light became white
once again. What did Sir Isaac Newton do? He first took the white light apart and then he put it back
together again.
All a prism does is refract light. White light is composed of many different frequencies and wavelengths
and a different frequency will correspond to a different color of light. When the light travels through the
prism, it slows the light down and will refract it. Each frequency that makes up the white light slows
down differently from each other, and thus refract
at different angles. Which is why the rainbow is
always in the order or red, orange, yellow, green,
blue, etc. because red light travels slower than
violet light when it travels through the prism, it will
refract at a higher angle than violet light
The most common example of a spectrum is the
rainbow created in nature.
The rainbow is caused by sunshine (white light)
shining on water droplets that are in the air just after
a summer shower. Thousands of these water droplets break up the light, just like Sir Isaac Newton's
prism. Can you make a rainbow? Of course! Make your own rainbow by turning on the garden hose,
which has a nozzle that will make a fine mist, or spray. Make sure the sunlight is coming over your
shoulder. You have made a rainbow.
Convex and concave are terms that are used to define two different types of curvatures. While
both convex and concave relate to some type of curve, they are never used to refer to the same
type of curve. However, it is usually possible to classify just about any incidence of curve as
either convex or concave.
In order to understand the difference between convex and concave
curvatures, it is first necessary to define each term. Convex relates to
a curvature that extends outward. The curve can occur at any point
along the surface of any object. Perhaps the classic example of a
convex curve would be the surface of a ball or sphere.
Concave indicates the presence of a curve that extends inward rather
than outward. When an object is concave in nature, the appearance is
a section between two points that may appear to be hallowed out. A
good example of a concave object would be a bowl or plate.
A transparent object is something that will allow all of the light rays to pass through it. Things like glass,
some kids of plastic and food wrap are transparent because of the density of the molecules inside it.
A translucent object is a material that will only allow some or a little bit oh the light rays to pass
through it. Things like wax paper, cloth and paper are translucent because of the density of the
molecules inside it.
An opaque object is something that will allow no light to pass through it because the density of
the object is too great. Things like wood folders and mirrors are opaque.
Lewis Latimer is considered one of the 10 most important Black inventors of all time,
not only for the sheer number of inventions created and patents secured but also for
the magnitude of importance for his most famous discovery. Latimer was born on
September 4, 1848 in Chelsea, Massachusetts. His parents were George and Rebecca
Latimer, both runaway slaves who migrated to Massachusetts in 1842 from Virginia.
George Latimer was captured by his slave owner, who was determined to take him
back to Virginia. His situation gained great notoriety, even reaching the Massachusetts
Supreme Court. Eventually George was purchased by abolition supporters who set him
free.
In 1880, after moving to Bridgeport, Connecticut, Latimer was hired as the
assistant manager and draftsman for U.S. Electric Lighting Company owned by Hiram Maxim.
Maxim was the chief rival to Thomas Edison, the man who invented the electric light bulb. The
light was composed of a glass bulb which surrounded a carbon wire filament, generally made of
bamboo, paper or thread. When the filament was burned inside of the bulb (which contained
almost no air), it became so hot that it actually glowed.
Thus by passing electricity into the bulb, Edison had been able to cause the glowing bright light to
emanate within a room. Before this time most lighting was delivered either through candles or through
gas lamps or kerosene lanterns. Maxim greatly desired to improve on Edison's light bulb and focused on
the main weakness of Edison's bulb - their short life span (generally only a few days.) Latimer set out to
make a longer lasting bulb.
Latimer devised a way of encasing the filament within a cardboard envelope which prevented the
carbon from breaking and thereby provided a much longer life to the bulb and hence made the bulbs
less expensive and more efficient. This enabled electric lighting to be installed within homes and
throughout streets.
Latimer's abilities in electric lighting became well known and soon he was sought after to
continue to improve on incandescent lighting as well as arc lighting. Eventually, as more major
cities began wiring their streets for electric lighting, Latimer was dispatched to lead the planning
team. He helped to install the first electric plants in Philadelphia, New York City and Montreal
and oversaw the installation of lighting in railroad stations, government building and major
thoroughfares in Canada, New England and London.