Ch. 22: The Nature of Light
What is an Electromagnetic wave?
An electromagnetic (___) wave is a ______________ that transfers energy through a _______. A field is an
______ around an object where the object can apply a _______ to another object without touching it.
How does an EM wave form?
__________ (____________ charged particles) move at different _________ from the nucleus depending on the
amount of energy it has. When an electron _________ energy, it can jump to a higher ___________ (________
from the nucleus). If an electron returns to its original position, it releases energy as a “___________.” A
stream of ____________ starts a ______________ of vibrating ____________ and _____________ fields
which carry the energy ___________ by the electrons.
A _____________ electric field generates a ____________ field and a ____________ magnetic field produces
an ___________ field. These fields move ________________ to each other ____ to the direction of ______ of
the wave. Together they form a ________ EM wave traveling as a ____________wave.
What is the source of most of the Earth’s EM waves?
The Sun’s high __________ allows it to give off countless EM waves. Other ________ produce EM waves, but
because they are so far away few of their waves reach Earth.
Why can EM waves travel through space?
Because EM waves are made up of ______ and not ________, they can transfer energy through space without a
__________. The transfer of energy in the form of EM waves is called ______________.
How do EM waves travel in a vacuum?
Because EM waves do not have to ____________ matter to move, it does not “_______” any energy as it
travels through space. EM waves from the Sun travel about _______________ miles to reach Earth.
In a _____________, EM waves spread ____________ in all directions from the source of the disturbance. The
wave then travels in a _____________ line until something interferes with it. The ___________ the waves
move from their source, the more they ____________ out. Only a _______ part of the energy ______________
from the Sun is transferred to Earth.
What is the Speed of Light?
In a vacuum, EM waves travel at a _____________ speed, and they travel very fast – about
___________________ m/s. Even at the _________ of _________, the Sun’s rays take about _____ minutes to
reach the Earth.
How to EM Waves Differ?
Even though all EM waves travel at the same __________, they can have different _______________ and
________________. The entire range of EM waves is called the ___________________
__________________.
The spectrum is a smooth, ___________ progression from the ____________ frequencies (longest
wavelengths) to the _____________ frequencies (shortest wavelengths). Divisions between the EM Spectrum
are ______ exact.
Radio Waves
Radio waves have the __________ wavelengths, the _____________ frequencies, and carry the ___________
energy.
Different radio stations broadcast at ________________ frequencies. The numbers (101.1 or 99.5) are the
frequencies they transmit at.
Simply transmitting EM waves at different frequencies is not enough to send music or words. The radio
transmitter attaches the information by _______________ (changing) the waves slightly. AM stations
broadcast using ______________ Modulation (the waves amplitude changes slightly) and FM stations
broadcast using __________________ Modulation (the waves frequency changes slightly.)
AM radio waves can ___________ off the ionosphere which helps AM waves travel _________ distances.
FM radio waves can ___________ through the ionosphere so they ____________ travel as far as AM waves.
There is a maximum of ________ FM radio stations to avoid interference of the frequencies.
A _______ also uses radio waves. The picture part is transmitted by _______waves and the sound part is
transmitted by _____ waves.
Microwaves
Microwaves are EM waves with __________ wavelengths, ____________ frequencies, and ___________
energy than radio waves. ________ and ________________ use microwaves.
Radar stands for “radio detection and ranging.” It was used in WWII to detect aircraft and ships from a distance.
Radar works by transmitting microwaves and receiving ________________ of those waves when they hit
objects. Radar led to the invention of the _____________________________.
Infrared Light
Infrared light waves are between ______________ and ___________ light on the spectrum. Infrared is most
commonly associated with ________. Waves in this range are sometimes called ______________. Although
we cannot see infrared waves, we feel the warmth from the Sun, a fire or a radiator. ________________ snakes
can see infrared light.
Humans can only see these frequencies using a device like an infrared camera, which shows warmer areas as
_____ and __________ and cooler ones as ______, _________ and __________.
Visible Light
Visible Light is a very _____________ range of the EM Spectrum. Humans see different wavelengths as
different _________. The longest wavelengths (lowest energy) are seen as _______ light and the shortest
wavelengths (highest energy) are seen as ___________ light.
Roy G. Biv = Red, Orange, Yellow, Green, Blue Indigo, and Violet.
When all of the colors of visible light are _________________ we see ____________ light.
Most of the visible light on Earth comes from the _______. The production of light by materials at high
temperatures is called ____________________. When a material gets hot enough, it gives off light by glowing
or bursting into flame. In a light bulb, the thin wire made out of ___________ offers a high resistance to the
electrical current. This causes the wire to get very hot and begin to glow. The tungsten filament actually
produces more _______________ light than visible light. Eventually the filament weakens and breaks causing
the light bulb to burn out.
Ultra-Violet (UV) Light
UV light has ____________ frequencies than visible light and carries more energy. They can ____________
tissue by burning your __________. Sunblock and UV-sunglasses filter out these frequencies.
UV light is used to ______________ the eye goggles in the classroom. They also cause skin cells to produce
________________, which is essential to good health. _________ are able to see nectar guides in the UV
range.
X-Rays
X-rays have very ________ wavelengths, _________ frequencies, and are very ________ energy waves. Xrays pass easily though the soft __________ of the skin, but are filtered out by _________. If photographic film
is placed behind the body only the x-rays that pass through the body will _____________ the film allowing for
doctors to diagnose bone ____________ and dense tumors. Too much exposure to x-rays can damage tissue
and cause cancer. _________ blocks out high-frequency radiation.
Gamma Rays
Gamma waves are the _______________ energy EM wave. They are produced by some
____________________ substances as well as the ______ and other stars. They can _____________ the skin
and hard tissues of the body, causing cancer. However, if used carefully, they can also be used to _____ cancer
cells and ________ tumors in _____________ therapy.
How Do EM waves Interact with a Medium?
_________________ is the passage of an EM wave through a medium. If the light _______________ from
objects did not pass through the air, windows or most of the eye, we could not see the objects.
Materials can be classified according to the amount of light they transmit:
1. _____________: most of the light passes through. Examples: air, water, clear glass
2. _____________: some light is transmitted, but they also cause it to spread out in all directions. Examples:
Lightshades, frosted windows, notepaper.
3. _____________: do not allow any light to pass though them because they reflect or absorb the light.
Examples: heavy fabrics, ceramic mugs, wood and rock.
A ___________________ is a material that is transparent to some kinds of light and opaque to others. For
example, red glass _______________ red light but ____________ other colors.
What is Absorption?
Absorption is the __________________ of an EM wave into the medium. For example: When you shine a
flashlight into the air, the air particles absorb some of the energy from the light causing the light to become dim.
What is Scattering?
Scattering is the ______________ out of light waves in all directions because particles ____________ the light.
When they _____________ the light, it scatters in all directions. Scattering makes the _______ blue.
Molecules in the Earth’s atmosphere scatter the blue _________________ more than any other wavelength.
What is Refraction?
Refraction of light is the ______________ of the wave as it passes at an ________ from one medium to another.
Light waves refract based on their _________________. A prism refracts light waves _______ – once when it
________ and once when it ________. _________ light (short wavelength) is refracted more than ______ light
(long wavelength). ________________ are created when sunlight is refracted by water droplets.
What is The Law of Reflection?
Reflection occurs when light bounces off an object. Reflection allows us to see objects that don’t produce their
own light.
The Law of Reflection states that the Angle of _____________ is equal to the Angle of ______________.
In _____________ reflection (a mirror), the light is reflected off all points at the ________ angle. In
__________ reflection (a wall), the light is reflected off at many ____________ angles because of the rough
surface.
How do we see an Apple as Red or Green?
The color of an opaque object is determined by the wavelengths it ___________ and ____________. A red
apple absorbs all color wavelengths except _____ and reflects ______. A green apple absorbs all color
wavelengths except _________ and reflects ________. A white object ____________ all of the wavelengths
and appears white. A black object ________________ all of the wavelengths and does not reflect any
wavelengths.
What are the Primary Colors of Light?
The human eye can only detect three colors – _____, ________, and ________. When all of the colors are
mixed equally we see _________ light. A color TV broadcast is made up of these three color pixels.
Combining colors of light is called color____________. When two primary colors are added together, a
_________________ color is produced (_______, ____________, and _________________.)
What are Pigments?
A pigment is a material that gives a substance a color by _________________ some colors of light and
______________ others. Almost everything contains pigments. Each pigment absorbs at least _____ color of
light. Mixing colors of pigments is called color _______________. When you mix pigments together, more
colors are ______________, or subtracted.