Light: Detection, Interactions, Transmission, Colors

Light Review

6.P.3.2

 Explain the effects of electromagnetic waves on various materials including absorption, scattering, and change in temperature.

ARGUE LIKE A SCIENTIST

Apple in the Dark

Imagine you are sitting at a table with a red apple in front of you. Your
friend closes the door and turns off all the lights. It is totally dark in the
room. There are no windows in the room or cracks around the door. No
light can enter the room.
Select the statement you believe best describes
how you would see the apple in the dark:
A You will not see the red apple, regardless of
how long you are in the room.
B You will see the red apple after your eyes have
had time to adjust to the darkness.
C You will see the apple after your eyes have had time to adjust
to the darkness, but you will not see the red color.
D You will see only the shadow of the apple after your eyes have
had time to adjust to the darkness.
E You will see only a faint outline of the apple after your eyes
have had time to adjust to the darkness.

Poll

Select your response:

• A

• B

• C

• D

• E

For an object to be visible it must
produce its own light or reflect light.
So the correct answer is…

LIGHT

A You will not see the red apple,
regardless of how long you are
in the room.

Visible light falls in the middle of the electromagnetic
spectrum. Light is the only form of EM radiation for which
human bodies have specialized sensory organs. The
human eye is extremely sensitive to light and color.

ELECTROMAGNETIC SPECTRUM

We depend on light for vision.
Most animals depend on visible light to find food and
do other things necessary for their survival.
Green plants need light to
make their own food and
to pass on their energy to
consumers.
Most living organisms
depend on light for their
existence.

VISIBLE LIGHT

Draw

Identify the natural vs artificial light sources

Most of the visible light waves in the environment come
from the Sun. The Sun’s intense heat produces light of
every wavelength. The production of light by materials at
high temperatures is called incandescence. When a
material gets hot enough, it gives off light by glowing or
by bursting into flames.

LIGHT

Many organisms produce their own visible light, which
they use in a variety of ways. They produce this light
through luminescence. Luminescence is the
production of light without the high temperatures
needed for incandescence. The production of light by
living organisms is called bioluminescence.

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LIGHT

Human beings invented
the first artificial lighting
when they learned to
make and control fire. For
most of human history,
people have made light
with devices that use fire
in some form, such as oil
lamps, candles, and
natural gas lamps.

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LIGHT

After the discovery of electricity, people began to make light through a
means other than fire. However, the technique of using a very hot material as
a light source stayed the same until the invention of fluorescent lighting.

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LIGHT

One of fastest-growing types of artificial lighting is the light
emitting diode, or LED. LEDs do not involve bulbs, filaments, or
gases. Instead, they produce light electronically. A diode is a
type of semiconductor—
a device that regulates
the flow of electricity.
An LED is a semiconductor
that converts electricity
directly into visible light.

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LIGHT

The Sun is a natural source for visible light waves and our
eyes see the reflection of this sunlight off the objects
around us.

But how do our eyes actually detect light waves?

DETECTING LIGHT WAVES

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Light travels in a straight path.
It travels 186,000 miles per second.
That’s like you going around the earth 7 ½ times in one second!

LIGHT INTERACTIONS

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Draw

Match the following:

Light can interact with
mediums in three
different ways:
• reflection

• absorption

• transmission

LIGHT INTERACTIONS

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Transmission is the passage of an
EM wave through the medium.
•If transmitted light has to go
around a barrier, diffraction will
occur.
•If transmitted light hits a bumpy
surface, diffusion will occur.
•If transmitted light enters a new
medium or a curved medium,
refraction will occur.

LIGHT TRANSMISSION

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Diffraction
•When light encounters a barrier
(obstacle or opening), it will bend
through or around.
•A new wave front is created.
•This appears as a softer light that

does not cause a glare or harsh
shadows.

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LIGHT TRANSMISSION

Diffusion
•When parallel rays of light hit a
bumpy surface, light is diffused.
•Each ray obeys the law of
reflection, but each ray hits the
surface at a different angle.
•The light is scattered.

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LIGHT TRANSMISSION

Refraction
•When light waves enter a new
medium at an angle, their speeds
changes.
•The change in speed causes
them to bend, or change
direction.
•Index of Refraction – a measure
of how much a ray of light bends
when it enters that material

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Index of

Refraction

LIGHT TRANSMISSION

Refraction
•Remember when we placed our
pencil in a cup of water and it
appeared “broken”?
•Light travels faster in the air than
in water, because the water
molecules slow the waves down.

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LIGHT TRANSMISSION

Materials can be classified according to the
amount and type of light they transmit.
Transparent materials allow most of the light that
strikes them to pass through. It is possible to see
objects through a transparent material.
Translucent materials transmit some light, but they
also cause it to spread out in all directions. You can
see light through translucent materials, but you
cannot see objects clearly through them.
Opaque materials do not allow any light to pass
through them, because they reflect light, absorb
light, or both.

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LIGHT TRANSMISSION

Reflection is when light bounces off an
object.
•Occurs when parallel rays of light hit a
smooth surface.
•All the rays are
reflected at the
same angle.

LIGHT INTERACTIONS

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When all of the wavelengths of
visible light are present
together, as in light from the
Sun or a light bulb, we see
ordinary light, which is also
called white light.

COLORS OF LIGHT

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Colors
•We see these separate waves as the
colors of the rainbow.
•Each color has a different wavelength
and frequency.
•Red has the longest wavelength and
shortest frequency.
•Violet has the shortest wavelength
and highest frequency.

COLORS OF LIGHT

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The color of an object or
material is determined by
the wavelengths it absorbs
and those it reflects.
An object has the color of
the wavelengths it reflects.
A material that reflects all
wavelengths of visible light
appears white.
A material that absorbs all
wavelengths of visible light
appears black.

COLORS OF LIGHT

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A green lime absorbs all colors except green and reflects

green, so the lime looks green, as shown below.

Green is our color perception.

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COLORS OF LIGHT