Drexel-SDP GK-12 ACTIVITY
Subject areas:
Unit title:
physical science (Astronomy)
Holt Astronomy activities
Activity title:
Grade level:
Reflection and refraction (Holt Chapter 1)
6
Time required: 60 minutes
Keywords:
reflection, refraction, light
Educational standards:
3.4.7D
Portions of this lesson plan were permissibly adapted from Joshua Faber
http://w3.physics.uiuc.edu/~jfaber/optics1.html
Concept/Vocabulary
In this activity, students investigate the behavior of light as it passes from one transparent medium
(air) to another (water). They will use and investigate the concepts of reflection and refraction by
studying the behavior of light as it travels through the air and through a tank of water. They will
also use the Holt text and other resources to review the astronomy terms:
• telescope
• refraction
• refracting telescope
• reflecting telescope
• electromagnetic spectrum
Students will exercise geometric concepts of angles and symmetry. They will practice measurement skills using sketches and protractors.
Objectives
• Students will learn and understand how light can be reflected and refracted.
• This activity will aid in the understanding of how light behaves in reflecting and refracting telescopes.
INSTRUCTIONAL STRATEGIES
Group size: This activity can be performed in groups of 4-6 students.
Duration: It can be performed in one class period.
Before
• Students will perform the Motivate Activity on page 8 of the Holt Astronomy Teacher Edition text.
They will construct a water drop lens. They should learn how light traveling through a lens can
be used to magnify an image.
During
•
A small rectangular fish tank (or other similar
small clear enclosure) should be set on top of
white sheets of paper. The paper should extend
out beyond the tank on all sides. The instructor
should fill the tank with water.
•
Students will be asked what will happen to light
if we shine a flashlight onto the surface. They
should be encouraged to briefly discuss within
groups the direction or directions the light will
travel.
•
One student from each group should stand on one side of the aquarium and shine a flashlight
on the surface. The other members of the team should stand on the other side of the tank and
note that some of the light is reflected at the water’s surface. Students should learn that when
we see light upon the surface, it is an indication that reflection is taking place (some of the light
is hitting the surface and bouncing into our eyes).
•
The students should now be asked if all the light is reflected from the surface. They should be
able to determine that some of the light is traveling down through the water. It may help if
students place their hands under the water to see that some of the light is indeed passing down
through the liquid. The light should also be visible on the white paper sitting beneath the tank.
•
Students should understand that transparent materials like water and glass can both reflect light
and transmit light. Ask them to think about another example of this concept (i.e. seeing your
reflection in transparent window glass).
•
Next, students should place a yardstick within
the water. Students should look at the yardstick
from a number of different angles, and note how
it appears to bend at the point where it enters
the water. Students should attempt to make a
few accurate sketches of the bending they observe. They can use protractors to estimate the
bending angle in these drawings. If a digital
camera and printer are available, it may be instructive to take photos of the ruler from various
points and have the students measure the angle
on printouts.
•
Students should be asked to think about whether the yardstick is truly bending when it enters the
water. Encourage the groups to feel the ruler as it enters the water to demonstrate that the yardstick remains straight, despite its bent appearance.
•
Remind the students that we see the yardstick because light reflects from it and enters our eyes.
Once they have verified that the ruler does not physically bend in the water, ask them to consider what might be bending instead. Students should identify that the light itself bends as it
travels from air to water. Introduce them to the term refraction – the process in which light
changes speed and direction when it passes between different transparent media (i.e. glass, air,
water). Ask the students to offer examples of refracted light they have encountered, such as the
apparent bending of a straw in a glass, or the optical illusion of shallow water in a deep swimming pool.
•
Finally, students will use a laser pointer to follow a path of light through the aquarium. Students
should be reminded that lasers are not to be shined in one another’s eyes.
•
In order to make the laser beam
visible in the water, it will be necessary to add a small amount of milk.
Depending on the amount of water
present, it may only be necessary to
add a few drops of milk. If too
much milk is added, it will not be
Portions of this lesson plan were permissibly adapted from Joshua Faber
http://w3.physics.uiuc.edu/~jfaber/optics1.html
able to travel through the tank.
•
Ask the students to think about why the milk allows us to see the laser beam. Encourage them
to consider the fact that the laser traveling through clear water travels in a straight line until it
reaches the other side of the tank. However, by adding milk (which contains small globules of
proteins and fats), the water becomes cloudier. The small particles within the milk cause the
light to scatter away from its straight path, and some of those scattered beams find their way into
our eyes, allowing us to see the laser light.
•
Draw a parallel to other phenomenon in the natural world where light is scattered by small particles. Ask the students to consider what makes beams of
light visible in fog or mist. They should learn and
understand that small droplets of water condensing in the air
will scatter light and make light beams visible.
•
Have the students try shining the lasers from various
directions and at various angles. First ask the students to
shine the laser straight through from the front of the tank to
a wall or sheet of paper behind the tank. Then, they should
direct the light through the front of the tank at an angle so
that it re-emerges from one of the sides. Finally, can they
shine the light through the front of the tank, hitting one of
the side walls, and bouncing out the back. These various angles are shown in the top-down view
here.
•
Finally, students should construct a rudimentary “telescope,” following the instructions of a basic kit such as the Anchor Optics kit B26057. They should be able to explain how light can be
manipulated by the lens to enlarge or diminish the size of an object.
Reading/Writing
The class will be reading the book Hatchet, by Gary Paulson. There will be a discussion of the scene
in pages 110-112, where the character Brian is trying to catch fish and learns that they are not where
they appear to be because of refraction.
Students will write a concise summary of the experiment in their science notebooks, focusing on a
simple hypothesis, method of testing, and results. They should be encouraged to briefly explore any
of their ideas that may have changed during and after the experiment.
Students may write a persuasive letter comparing and contrasting various types of telescopes, as
listed on the Alternative Assessment on page 12 of the Holt Astronomy Teacher Edition text.
Cultural Connection
Student groups will prepare oral presentations to describe the contributions of famous astronomers
like Brahe, Kepler, Galileo, Newton and Hubble to modern astronomy.
PSSA
What provides the best evidence that light is a form of energy?
A. Light reflects from a smooth surface.
B. Light raises the temperature of an object it strikes.*
C. Light travels in a straight line until it strikes an objects.
D. Light diffracts when it passes through a narrow opening.
Owner: Drexel University GK-12 program, Engineering as a Contextual Vehicle for Science and
Mathematics Education, supported in part by National Science Foundation Award No. DGE-0538476
Author: Matthew D. Cathell
Copyright: Copyright 2007 by Matthew D. Cathell
Portions of this lesson plan were permissibly adapted from Joshua Faber
http://w3.physics.uiuc.edu/~jfaber/optics1.html