LIGHT AND SOUND
LESSON 6
Summary
Students learn the five words that describe how light interacts with objects: transparent, translucent,
opaque and refraction. This is the first lesson of this unit to introduce light.
Engineering Connection
Being able to see is crucial for many things that we do everyday. Engineers and scientists have created
lighting devices to help us see in the dark. Lighting engineers design the illumination systems in the places
we live and work. Without their expertise, our day-to-day sight could be worse (than it might already be)
due to poor lighting conditions and eye strain. Their understanding of how light works enables engineers
to create new types of lighting and design light bulbs and fixtures that are more energy efficient and easier
on our eyes.
Learning Objectives
After this lesson students should be able to:
• Explain reflection and refraction.
• Give examples of something that refracts light and something that reflects light.
• Provide a basic explanation of the following terms: transparent, translucent and opaque.
Introduction/Motivation
If you recall, the natural gas bubbles were good sound absorbers, preventing the sonar from reaching
the galleon on the bottom of the sea. But the bubbles have passed, and Angie, Harmon and Fisherman
Frank can now see the outline of a ship on the ocean floor using the sonar. They want to go down and
take a look, but there is no light on the bottom of the ocean. How are they going to see underwater?
Angie, Harmon and Fisherman Frank desperately want to see the ship with their own eyes, and to do
that they need light. Light, even though it is all around us, can be tough to understand. Today we are
going to focus on learning five words that scientists and engineers use to explain how light interacts
with different types of objects, or materials. The five words that we are going to talk about today are:
transparent, translucent, opaque, reflection and refraction.
Teacher demonstration (then, you’ll try this at home with your parents):
1 Hold up a flashlight to a clear piece of glass. Does the glass transmit (let through) light? If so, the
glass is transparent to light.
2 Next, hold up the flashlight to a piece of wax paper. Does the wax paper transmit light? Very
likely, some light goes through, but some does not. In other words, some of the light is transmitted
through the paper, but some is absorbed and some of it is reflected (it bounces off). Therefore, we
say that the wax paper is translucent. What are some other things that might be translucent?
3 Now hold the flashlight up to a book. Does the book transmit light? Obviously, the answer is no.
Th light is absorbed and a little is reflected. We say that the book is opaque to light. Can you think
of other things that are opaque?
4 What happens if you shine a light into a mirror? Mirrors and other surfaces reflect light.
5 Try looking through a plastic water bottle. Do objects behind it look the same? The answer is no
and the reason objects look different is that the transparent material is bending the light that comes
through it, changing its shape. The tendency of a light wave to bend as it passes from one
transparent medium to another is called refraction.
Reflection and refraction are alike in that they change light's direction. What makes them different is
whether light goes through the material or not. When light is reflected, it bends away from the surface
and does not pass through the material. Refraction occurs at the border between two transparent
mediums as light passes through the object. The light is bent, as in reflection, but it bends into the
material, rather than away from it.
Now let's think about our two brave adventurers! In order to see the sunken ship, Angie and Harmon
are going to have to find some way to take light down with them to the ocean floor. Does anyone have
any ideas how they can do this? Let's find out!
Vocabulary/Definitions
opaque: None of the light goes through; it is either reflected or absorbed.
reflection: The direction of light is changed; it is as if it bounces from the surface.
refraction: The tendency of a wave to bend as it passes from one transparent medium to another.
translucent: Lets some of the light through; gives off a diffuse glow (not as image preserving as
transparent glass).
transparent: Lets most of the light through; images are preserved.
Lesson Closure
You have all learned a lot about light in this lesson! You learned that engineers design and build lights for
us to see by, and lighting engineers design lighting systems for many different places. You also learned
five new vocabulary words! Now you are going to get the chance to explore some of these amazing
properties of light for yourselves, and use your new vocabulary words to explain what you discover. In
our next lesson, we will continue to explore light and learn which lights Angie and Harmon use to explore
the sunken ship.
Homework
Try this at home with your parents:
1 Hold up a flashlight to a clear piece of glass. Does the glass transmit (let through) light? If so, the
glass is transparent to light.
2 Next, hold up the flashlight to a piece of wax paper. Does the wax paper transmit light? Very
likely, some light goes through, but some does not. In other words, some of the light is
transmitted through the paper, but some is absorbed and some of it is reflected (it bounces off).
Therefore, we say that the wax paper is translucent. What are some other things that might be
translucent?
3 Now hold the flashlight up to a book. Does the book transmit light? Obviously, the answer is no.
Th light is absorbed and a little is reflected. We say that the book is opaque to light. Can you
think of other things that are opaque?
4 What happens if you shine a light into a mirror? Mirrors and other surfaces reflect light.
5 Try looking through a plastic water bottle. Do objects behind it look the same? The answer is no
and the reason objects look different is that the transparent material is bending the light that
comes through it, changing its shape. The tendency of a light wave to bend as it passes from one
transparent medium to another is called refraction.