Lesson: Direct and Diffuse Light
Create an understanding of the difference between direct and diffuse light
Teacher starts by shining the flashlight onto the posterboard first perpendicular
to the board and then at an angle. The teacher asks: "Which light is brighter?"
"Why? Have we changed the brightness of the flashlight?"
You will need a flashlight and a piece of posterboard. Have the class sit
in a semi-circle around you and hold the posterboard so that everyone can
see it. Dim the lights and shine the light on the board so that the light
is perpendicular to the board. Ask a student to outline the pattern the
light makes on the board. Shine the light at a shallow angle to the board
on a different area of the board. Ask a student to outline the pattern
the light makes. Now ask the class what they notice. Possible questions
Divide students into groups of three or four. Each group will need watercolors
and a piece of non-absorbant white paper. Have the students fill in both
the circle and the oval with water using their paint brushes.
Describe the shapes of the outlines.
Which outline is larger?
Which outline has the bigger area or takes up more space?
Which pattern is brighter or more intense (may need to repeat the demonstration)?
Which light is more diffuse, less intense, or more spread out?
Next, have one student dip the brush in the blue paint. The student
should make seven drops in the circle of water. Have the next student make
seven drops of blue paint in the oval of water. Ask each group to make
observations about their circles and ovals to share with the class. Some
possible questions are:
Group students into groups of three or four. Each group is given two styrofoam
cups with the bottom one-quarter inch filled with uncooked popcorn. On
a plain piece of paper have one student pour the cup of corn out slowly
and carefully to make a small circle of popcorn. Have a student draw a
circle around the popcorn kernels. On a larger sheet of paper have another
student pour out the second cup of corn more quickly so that the corn spreads
out on the paper. Have a student draw a line around perimeter of the pattern
of popcorn. Ask each group to discuss what they notice about the shape
of each popcorn pattern. Some possible questions are:
Which shape has the brighter (more concentrated) color, the circle or the
Which pattern covers more area?
In which shape is the color more spread out, or diffuse?
Describe the shape of the popcorn pattern.
Which pattern is larger?
Which pattern has a bigger area (takes up more space)?
Which pattern has the popcorn more concentrated?
Which pattern is the popcorn more spread out (or diffuse)?
What simularities have you noticed between the experiments we have done
today? Summarize the popcorn, watercolor and flashlight experiments. Possible
Smaller circles or areas were brighter, more concentrated or more intense.
Larger circles or patterns were more spread out, diffuse, or less intense.
Listen to discussion of conclusion for student's ideas and redirect if
Prepare a sheet asking what students noticed and include vocabulary words.
Have the students make a picture or painting showing the concepts of diffuse
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