Light
Activity description: Investigate the behavior of light
Kit contents: flashlight, spool (or other opaque object), beaker, hand lens
Science Standards: SC.5.P.10.1 Investigate and describe some basic forms of energy, including light,
heat, sound, electrical, chemical, and mechanical.
SC.3.P.10.3 Demonstrate that light travels in a straight line until it strikes an object or travels from one
medium to another. (Review from 3rd grade)
SC.3.P.10.4 Demonstrate that light can be reflected, refracted, and absorbed. (Review from 3rd grade)
Basic Activity
Activity 1.
Materials: Solid opaque object (spool), flashlight, ruler.
Step 1. Measure the height of the wooden spool.
Step 2. Place the spool 20 cm from the wall. Place the flashlight 10 cm from the spool, 30 cm from the
wall.
Step 3. Shine the flashlight on the spool and measure the height of the shadow it makes on the wall.
Step 4. Place the spool 25 cm from the wall, leaving the flashlight in the same position.
Step 5. Shine the flashlight on the spool and measure the height of the shadow it makes on the wall.
Activity 2.
Materials: flashlight, ruler, clear glass/beaker, water, hand lens
Step 1. Place the flashlight 25 cm from the wall. Observe the light as it shines on the wall.
Step 2. Place the beaker filled with water between the flashlight and the wall, about 5 cm from the
flashlight. Observe the light as it shines through the water onto the wall. Does the light look different
when it passes through the water?
Step 3. Place the magnifying glass in the same place as the beaker. Observe the light as it shines through
the lens onto the wall.
Key Knowledge
Vocabulary
Absorb—To take up and store energy without reflecting or transmitting that energy.
Reflect—To bounce light, sound, or heat off of a surface.
Script Idea
What we will learn about today--light!!
What do the students know about light? Likely they will mention that it travels in a straight line.
What happens if some object gets in the way of the light? You get shadows.
Let's investigate shadows. Explain that you will give the kids five minutes to make some observations
about shadows using flashlights and spools (or whatever other objects you choose). After they make some
observations, you will regroup and come up with some questions to explore. Pass out the flashlights and
spools.
After 5 minutes, regroup. Ask the kids to name some of the things they observed. They probably noticed
that shadows are larger or smaller depending on the position of the object. They might have also noticed
that the shadows are more "crisp" when the object is closer to the wall (or other surface). Ask the students
what their ideas are for why they observed these things. See if they can come up with an experiment to
test their ideas. (If necessary, guide them to the Basic Procedure.)
Once the students have created their experimental plan, pass out the necessary materials and allow them
to try it. Ensure that they are recording their data. Encourage them to make measurements at multiple
point and possibly graph the results.
After about fifteen minutes, gather the students. Ask if they have ever seen light not travel in a straight
line. What else can light do? Reflect and refract (bend). Pass out the lenses and beakers. Give students
about five minutes to make observations. Encourage them to write them down in their science journal (or
other note paper).
Gather the students and ask them to describe some of the things they have observed.
Optical Science
How a lens works. Light travels at a uniform speed through a vacuum. However, as light enters different
mediums with different densitites, its speed changes. If light enters a new medium at an angle, the change
in speed causes the light to bend. This can be seen by putting a pencil in a glass of water. If you hold the
pencil straight, it will look uniform. If you have the pencil enter the water at an angle, it will look like it is
in two separate pieces.
An image of light passing through a convex lens is available here:
http://content.answers.com/main/content/img/ahd4/A4lens.jpg (the upper image).
In the image, the focal point is indicated by f. If you have your eyes between the f and the lens, the image
will be right side up, past the f it will be upside down.
Additional Demonstrations
Jello Optics Unflavored gelatin makes interesting lenses that show the light traveling through them. Kids
can see light bend and also reflect within the jello. See Jello Optics.
Mirrors. There are many interesting activities kids can do with mirrors, particularly if you have hinged
mirrors (or enough handheld mirrors that kids can have a couple). Interesting things that they can do
include: two mirrors at a 90 degree angle, with each perpendicular to the plane of the table, from each
other show your face as others see you, but if you turn them so that the planes are perpendicular to the
wall, you appear upside-down. Have a student draw an outline of their face on a mirror up close. Then
have them walk away--their face will continue to fill that outline (as long as they try to line it up).
Spectroscopes. Spectroscopes divide light into the spectrum. Light from the sun is pretty uniform across
the visible spectrum, but other light sources emit light of distinct wavelengths. This is why things seem
different with fluorescent or incadescent light. This is also why scientists use telescopes of different types,
such as x-ray or gamma ray. A CD spectrometer is pretty inexpensive to make. For instructions, see:
http://www.cs.cmu.edu/~zhuxj/astro/html/spectrometer.html
Jello Optics
Safety Note: This activity uses laser pointers. They can cause damage if shined in someone's eye,
particularly if they are shined through a magnifying lens. Students should only use them under close
supervision. Consider setting this activity up as a single table that the students rotate to, a table with a
dedicated adult supervisor.
Learning goals:
Lenses—light changes angle as it goes through different mediums, concave lens spreads light out, convex
lens focuses it in.
Focal point, concave, convex, reflection, refraction
Materials:
For pre-preparation:
unflavored gelatin
For every group of 4-5 students:
laser pointer
protractor
Activity
Pre-preparation: Making Jello lenses.
Follow directions on gelatin box (Knox sells unflavored, clear gelatin) EXCEPT only use hot water to
make stiff Jello. Pour into pans to make 1 inch thick. Cut cooled jello into rectangles, convex, concave
lenses (use round cookie cutter or just a knife). Try to make the cuts as smooth as possible.
Exploring lenses
Each table should have: assorted jello lenses, protractor, laser pointer
Allow students to explore how the light travels through lenses
Questions for the students as they explore: Where does the light go? Does the light stay on the same side
of the lens as it goes through? Does it cross the middle at some point? Can they make the light bounce
inside the lens? What angle does the light come out compared to the angle it went in?
Discussion
What did the students observe? Might try to expand to what they think things would look like through the
lens—tall and skinny, short and fat. Do things stay the same orientation? Perhaps compare to a spoon
(concave inside, convex outside). Try to eventually get to the idea of focus, perhaps to focal length.