Richard Rasmussen
PURPOSE (OPTICS UNIT)
The purpose of this introduction to our “optics” unit is to introduce students to the electromagnetic
spectrum, focusing on visible light. Students will be introduced to the idea that all light travels as waves,
and that wavelength defines the various regions of the electromagnetic spectrum.
CONTEXT
Many of us do not think of light as something that travels from one place to another, and most tend to
identify light with its source (e.g., light is in the bulb) or its effects (e.g., a patch of light). As a result, we
may have difficulty explaining the direction and formation of shadows, as well as reflection of light by
objects.
We usually understand that mirrors reflect light. Many of us may not believe that your eyes actually
receive light when looking at an object. We will be making pinhole cameras soon to help demonstrate this
idea.
LETS PLAY WITH PRISMS
Mr, Raz will provide each group of students a prism. You will have time to use the prisms to break up the
white light of the room, a flashlight, or sunlight coming into the room. You may use the overhead projector
by setting a prism on it to project the visible light spectrum onto the projection screen.
Please answer the following questions:

What do you see when you play with the prism?

What are the colors of the "rainbow"?

Are these colors distinct, or do they seem to blend together?
Visible light is light they we can see. We will be learning about light that cannot be seen, as well as about
how light travels.
Richard Rasmussen
WEBQUEST DEVELOPMENT
Please access the Making Light of Science site to answer the questions below.
The prism was a demonstration of the visible light spectrum, within the electromagnetic spectrum about
which you just read.

What is the electromagnetic spectrum?

What is the light that humans can see called?

How does light travel?

What are the high and low points of a wave called?

Define “wavelength”?

How is wavelength important in defining the regions of the electromagnetic spectrum?

What is the common measurement of a wavelength called?

How are light and ripples in a pond similar?

How does wavelength change as you move from left to right along the electromagnetic spectrum?

What region of the electromagnetic spectrum consists of light humans can see?

What are the other parts of the electromagnetic spectrum?
Richard Rasmussen

How do our eyes perceive color?

What type of light does the ozone layer protect us from?

Which type of light has the shortest wavelength and the most energy?
Now, Mr. Raz will do the classic Slinky demonstration to further explore the nature of waves. Stretch the
Slinky across the room so everyone can see it; you should hold one end and have a student volunteer
hold the other end. Slowly move your end of the Slinky to form waves. Practice with the Slinky until you
are able to generate standing waves, or waves that don't appear to move.
Generate a standing wave and ask these questions:

Where is the peak of the wave?

If we were going to measure the wavelength of this wave, where would we measure?

According to what we learned on the websites, do “long” or “short” waves have more energy?
Now, (teacher demo) Mr. Raz will move the Slinky slowly to generate long wavelengths. students need to
observe closely. Mr. Raz will make waves of much shorter wavelength by moving the Slinky very quickly.
(Be sure to move the Slinky approximately the same distance each time so that the waves all have about
the same height.) If done just right, this may demonstrate that the short waves have more energy. If so,
ask students if they can draw that conclusion from this demonstration.
Play with the prisms again to once again explore and see the various colors of the rainbow. At this time,
you should better understand and be able to explain in scientific terms how the prism works.
Please answer the following questions:

In what century was the visible light spectrum first observed? By whom?

Explain how the prism works (i.e., how it breaks light into a rainbow). Explain this using words
and an illustration. (As stated on the "Light Facts" page)