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Light Interactions
What is light?
• Light is an electromagnetic (EM) wave.
• An EM wave is a wave that consists of changing electric
and magnetic fields.
• EM waves require no matter through which to travel.
• EM waves can be produced by the vibration of charged
particles.
• The speed of light in a vacuum is about 300,000,000
m/s.
• EM waves from the sun are the major source of energy
for Earth.
The Electromagnetic Spectrum
• All electromagnetic (EM) waves travel at the
speed of light. EM waves differ only by
wavelength and frequency.
• The entire range of EM waves is called the
electromagnetic spectrum.
Radio waves are used for
communication.
• AM means amplitude
modulation
• FM means frequency
modulation
• PhET Simulation
Microwaves are used
in cooking and in radar.
• PhET Simulation
The absorption of infrared waves is
felt as an increase in temperature.
Visible Light
Visible light is the narrow range of
wavelengths that humans can see.
Different wavelengths are seen as
different colors.
Ultraviolet Light
• Killing bacteria
• Producing vitamin C
• Can cause sunburns
Bees see UV light…
• So they see the world
differently than we do!
X-Rays
Gamma Rays
Light Interactions
• The law of reflection states that the angle of
incidence is equal to the angle of reflection.
• Things that are luminous can be seen because
they produce their own light.
• Things that are illuminated can be seen because
light reflects off them.
• Absorption is the transfer of light energy to
particles of matter.
• Scattering is an interaction of light with matter
that causes light to change direction.
Light Interactions
• Refraction of light waves can create optical
illusions and can separate white light into
separate colors.
• Diffraction depends on the light’s wavelength.
– Light waves diffract more when traveling through a
narrow opening.
• Interference can be constructive or destructive.
– Interference of light waves can cause bright and dark
bands.
Law of Reflection:
angle of incidence = the angle of
reflection
Absorption & Scattering
Refraction
Refraction
Diffraction & Interference
Do You See What I See?
March 27, 2015
• Do Now: Angles of Reflection (share
protractors)
• Take out HW
• No homework tonight 
Light & Color
• Objects are transparent, translucent, or opaque
depending on their ability to transmit light.
• Colors of opaque objects are determined by the color
of light that they reflect.
• Colors of translucent and transparent objects are
determined by the color of light they transmit.
• White light is a mixture of all colors of light.
• Light combines by color addition. The primary colors of
light are red, blue, and green.
• Pigments give objects color. Pigments combine by color
subtraction. The primary pigments are magenta, cyan,
and yellow.
Objects are transparent, translucent,
or opaque depending on their ability
to transmit light.
Colors of opaque objects are
determined by the color of light that
they reflect.
Colors of translucent and transparent
objects are determined by the color of
light they transmit.
Light combines by color addition.
The primary colors of light are red,
blue, and green.
Pigments combine by color
subtraction.
The primary pigments are
magenta, cyan, and yellow.
Question 1
Ultraviolet light has a higher frequency than
infrared light has. Which statement about visible
light is true?
A. Blue light has a longer wavelength than orange
light has.
B. Green light has a higher frequency than violet
light has.
C. Yellow light has a shorter wavelength than blue
light has.
D. Red light has a lower frequency than green light
has.
Question 1
Ultraviolet light has a higher frequency than
infrared light has. Which statement about visible
light is true?
A. Blue light has a longer wavelength than orange
light has.
B. Green light has a higher frequency than violet
light has.
C. Yellow light has a shorter wavelength than blue
light has.
D. Red light has a lower frequency than green
light has.
Question 2
Which light interaction explains why you can see
things that do not produce their own light?
A. absorption
B. reflection
C. refraction
D. diffraction
Question 2
Which light interaction explains why you can see
things that do not produce their own light?
A. absorption
B. reflection
C. refraction
D. diffraction
Question 3
Which electromagnetic waves is the eye able to
see?
A. Red, green, and ultraviolet
B. Red, infrared, and yellow
C. Blue, green, and ultraviolet
D. Orange, green, and red
Question 3
Which electromagnetic waves is the eye able to
see?
A. Red, green, and ultraviolet
B. Red, infrared, and yellow
C. Blue, green, and ultraviolet
D. Orange, green, and red