Model Lesson I
Shadows
SOL(s):
PS.9.b: the wave behavior of light;
ES.3.b: sun-Earth-moon relationships; (seasons, tides, and eclipses);
Instructional Objectives:
SWBAT observe shadows created by single and multiple point sources.
SWBAT identify the umbra and penumbra of a shadow made from a single source and one made from multiple sources.
SWBAT explain how the following variables: light spacing, object width, and distance between light and an object influence the shape of the umbra and penumbra of a
shadow.
Lesson
Segment &
Time Est.
Introduction
(Predict,
Explain)
Materials
PowerPoint
introduction
slide
Instructional Sequence
How are shadows formed? (Show image as this question is asked.)
Teacher/Student
Actions
T. show ppt and elicits s. prior
knowledge.
Based on the labs you did yesterday, do shadows become “fuzzy” as objects move closer to the light
source? Why do you think their fuzziness changes as objects move toward or away from light?
15 minutes
Worksheet
with
prediction
scenarios
Body
(Observe)
(Explain)
25 minutes
Penumbra
Effect
ExploreLearn
ing Gizmo,
worksheet
Predict: Elicit Students’ Ideas:
Predict how the following factors affect the shape/size/location of the umbra (dark shadow) and
penumbra (lighter shadow) of a shadow: light spacing, width of the object, and distance between the
lights and the object. Be sure to provide a rationale for each prediction based on the nature of light and
that relates to the interactions between the light and the object.
Explain: Discuss students’ predictions: S. share predictions/explanations in a class discussion. Make
sure to value all ideas. Discuss s. predictions and rationales and have s. discuss, given the range of
predictions, which might be most reasonable.
Observe: S. use the Gizmo to test their predictions. S. write down their observations and initial thinking
about the patterns they are seeing, relationships they are noting and rationales for their observations.
Q: What is the relationship between the number of light sources and the number of gradations observed
in the penumbra?
Q: How does the length of the umbra change as the distance between the object and the light source
increases or decreases?
S. make predictions and
explanations for their
predictions.
T. leads discussion of s.
predictions/explanations.
S. work in small groups to
change variables on the Gizmo
to test their predictions/answer
the research questions. T.
circulates and asks s. about
their observations and
explanations for their
observations.
Explain: (Small groups) S. discuss their observations and their explanations for these observations in
small groups then develop written explanations about the nature of light and shadows for the patterns
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Model Lesson I
Lesson
Segment &
Time Est.
Closure
(Explain,
con’t)
10 minutes
Total Time =
50 minutes
Materials
Instructional Sequence
they observe.
Explain (continued): Whole-class discussion of small group observations/explanations.
Teacher/Student
Actions
T. leads whole class
discussion.
Closure: Reiterate patterns s. noticed, provide scientific vocabulary and scientific explanation for
observations:
When light is emitted from a point source, it radiates into space in all directions. If an object is placed in
the path of the light, the resulting shadow will be completely dark as 100% of the light is blocked within
the shadow. This type of shadow is called an umbra.
If light is emitted from more than one source (or the light source is not a single point), the umbra will be
surrounded by an area where only part of the light is blocked. This region is the penumbra. If the light
comes from a series of point sources, the penumbra will show stepped gradations that are darkest next to
the umbra. If the light comes from a single, wide source, the penumbra will grade continuously from
light to dark.
1. The farther the object is from the light source, the more parallel the light rays are when they hit
the object. This will have the effect of narrowing the penumbra and lengthening the umbra.
2. Increasing the spacing of the light sources (or the width of a single light source) will make the
penumbra wider and the umbra shorter.
3. Making the object wider will have the effect of lengthening the umbra and widening the
penumbra.
4. The size of the observed penumbra is also affected by how close the object is to a screen, wall,
or sheet of paper that the shadow is projected onto.
5. The closer the object is to its shadow, the smaller the observed penumbra will be. This explains
why the shadow of a marker is much sharper when the marker is held close to a screen.
Extension question: Consider the artwork we observed at the beginning of the lesson. Based on what
you know about shadows, do you think the shadow was made from one light source or many? Why?
Were these broad light sources or multiple point sources? Why do you think so?
Assessment
Plan:
During an eclipse, one body moves into the shadow of another. Predict what you would see during a
lunar eclipse, when the Moon moves into Earth’s shadow? (Hint: The Sun is a wide source of light, not a
point source.)
1. What is the relationship between the light spacing and the shape of the umbra?
2. What is the relationship between the object width and the shape of the umbra and penumbra?
3. Predict what you would see during a lunar eclipse, when the Moon moves into Earth’s shadow?
(Hint: The Sun is a wide source of light, not a point source.)
.
2
Model Lesson I
EXPLORING SHADOWS!
1. Predict the relationship between the following (drawings of your predictions are fine):
a. Nature of the light source (point source vs broad source) on the nature of the lighter
(penumbra) and darker (umbra) parts of the shadow:
b. Number of lights (assume these are point sources) and the nature of the penumbra and
umbra parts of the shadow:
c. Distance between lights and the shape of the penumbra and umbra
d. Object width and the shape of the penumbra and umbra
e. Distance between the light(s) and the object on the shape of the penumbra and umbra
f. Distance between the object and its shadow on the shape of the penumbra and umbra
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Model Lesson I
2. Use the Gizmo to test your predictions. Before testing your predictions familiarize yourself
with the Gizmo by changing each variable to see what they do and turning on and off the ray
tracing and light intensity check boxes.
3. Systematically test your predictions and record your observations below. You can write or draw
your observations. Make sure to describe any patterns or relationships you notice and
explanations for your observations.
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