Light is a form of electromagnetic radiation that can be described as a stream of massless particles called photons traveling in wave-like patterns. Electromagnetic radiation includes visible light as well as other wavelengths and includes properties like wavelength, frequency, and speed. Light travels in straight lines and can be reflected, refracted, and separated into colors using a prism. The sky appears blue during the day due to scattering of blue light by dust in the atmosphere.

1. Light
Dixie STEM Workshop
Dr. Tracey Wheeler

2. What is Light?
• Light is a form of electromagnetic radiation.
• What is electromagnetic radiation?

3. Electromagnetic Radiation
Electromagnetic radiation can be described in terms of a stream of
mass-like particles, called photons, each traveling in a wave-like
pattern at the speed of light. Each photon contains a certain amount
of energy.
Starting with the lowest energy (longest wavelength) and moving to
the highest energy (shortest wavelength). This is often referred to as
the electromagnetic spectrum.
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

4. Properties of Electromagnetic
Radiation
• Travels in waves and is referred to
electromagnetic waves
• Electromagnetic waves travel at the
same speed but differ in wavelength and
in frequency. All electromagnetic waves,
including light rays travel in a vacuum at
a speed of light- 186,282 miles/second.
It takes 8 minutes for light to travel from
the Sun to Earth.
• Does this mean that the distance light
travels depends on size or brightness of
the light source?

5. Wavelength
A wavelength is
the distance
between
corresponding
parts of two
waves with the
same motion.

6. Wavelength, Velocity, Frequency,
and Speed
Frequency- the number of waves that pass by a point in
a specified amount of time.
Speed- equals the wavelength x frequency

7. Frequency
Waves with long wavelengths have low
frequencies; waves with short wavelengths have
high frequencies.

8. Visible light
• Visible light -Cone-shaped cells in our eyes
act as receivers tuned to the wavelengths
in this narrow band of the spectrum.
Other portions of the spectrum have
wavelengths too large or too small and
energetic for the biological limitations of
our perception. Visible light 700 nm to
380 nm
• Do nocturnal animals see in total
darkness?
• http://www.ebiomedia.com/how-do-
animals-see-in-the-dark.html

9. Properties of Light
Light travels in straight
lines, even when it is
made to change
direction.
1. A thin line of light is
called a ray.
2. A beam of light is made
up of many rays.
3. Light travels faster than
sound- astronomers use
it for measuring great
distances.

10. Reflection
To see an object that does not
produce it's own light, three
things must happen.
1. There must be a light source
2. The light must strike the
object
3. The light must be reflected
from the object and then travel
to the eye.
Can light travel around things,
not just in straight lines?

11. Refraction of Light
When light rays strike a transparent material at an angle of 90
degrees, they travel in a straight line and gradually slow down.
When light rays pass at a slant or angle from one transparent
material (air) into another transparent material (water) they are
bent or refracted, so they travel in a different direction. Light is
bent because there is a change in the speed of light as it passes
from one transparent material into another. This depends on the
materials optical density.

12. Color
• When a beam of sunlight is passes at a slant into a prism, it is
separated into a band of colored light, called the spectrum
(visible light)
• White light is really a mixture of six colors
• Colors make up the spectrum all have different wavelengths
• Blue light is the shortest wavelength

13. Color
• A material looks a certain color
because when white light
strikes the material, some
colors are absorbed and others
are reflected to the eye.
• For example, a red dress may
look red because all the colors
of white light are absorbed
except red, which is reflected
back to the eye.

14. Why during the day does the sky
appear blue?
Sky appears blue
because blue light
is scattered by the
dust and reflected
to the eye much
more than are the
other colors.
Is color a property of
reflected light?