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Title: Candy, Lasers and the Properties of Light
Principle(s) Investigated: Students will explore the the behavior of white light and monochromatic light (green and red lasers) as it is shined on opaque, translucent and transparent candies. Students will be able to differentiate between absorption, transmission, and reflection.
Standards:
MS-PS4.B When light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object’s material and the frequency (color) of the light.
Materials:
Green Laser (Amazon or Office Supply Store)
Red Laser (Dollar Tree or 99 cent Store)
Gummy Bears
Jolly Ranchers
LED Flashlight
White Piece of Paper
Transparency or Plastic Bag
Wax Paper
Procedure: This lab can be set up as a demo, a group lab or a station lab. I usually make this a station that students rotate through.
1. Formative assessment of Prior Knowledge (Have the students use the google sheet to answer questions on the what do you think sheet).
2. To review the terms, shine the lights on the transparency, wax paper, and and white sheet of paper.
What do you see?
How would you describe the behavior of the light with the objects?
2. Have the students use the LED white light to shine on the objects. Have the students record observations in the data table.
3. Have the students use the red laser to shine on the objects. Have the students record observations in the data table.
4. Have the students use the green laser to shine on the objects. Have the students record observations in the data table.
5. Have some students share what they wrote in the observations section.
Student prior knowledge: Students should know how we see objects. We see objects when there is a light source and a direct path of light from the source to the object and to our eye. Students should know that light travels on waves and that the electromagnetic spectrum is made up of light with varying wavelengths. hat prior concepts do students need to understand this activity?
Explanation: Transmittance is the fraction of incident light at a specified wavelength that passes through something (like a gummy bear). Mathematically, transmittance is the ratio of the intensity of the light that passe through a sample to the intensity of the light when it entered the sample or T = I out / I in Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Absorbance is the measure of the quantity of light that a sample neither transmits nor reflects e a thorough explanation of the experiment or demonstration.
Questions & Answers: Ask students to share their observations
Did all light sources behave the same?
When did you observe absorption, transmission and reflection?
Why did the green light not pass through the red gummy bear?
And why did the red laser light not pass through the green gummy bear?
Why did the white light become red when it passed through the red gummy bear and become green when it passed through the green gummy bear? students to share their observations
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Applications to Everyday Life: Light shines on objects. Some of that light is reflected, transmitted, and absorbed. The color that an object appears to us is dependent on what wavelengths are reflected back to our eyes. Many students think that we see a color because it is absorbed. Hopefully this lab will help students to clear up this misconception. The way in which we see color is due in large part to the way light interacts with matter. So the color was never in the object...only in the light that shines upon it and ultimately is reflected to our eyes. No matter how many times you say it...is difficult for students to grasp the idea that when they see an object as red, what’s really happening is that most of the wavelengths that make up white light are being absorbed by the object and only the wavelength we know as red is being reflected. What they “see” is the red light transmitted to their eyes.
Virtual Lab The effects of colored light on photosynthesis
Photographs:
LED White Light Source
Green Laser Light Source
Red Laser Light Source
Videos:
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