Three different experiments are described below.
Instructions and a set of questions for these experiments can be found in the Shedding Light Experiment packet.
Choose one or more of these experiments for your students to conduct, and distibute the appropriate pages from the Experiment packet. If you do not wish to conduct any of these experiments, a set of sample data is available in the Questions for Students section.
Another set of sample data can be obtained from the Plexiglas video clip, which shows students conducting the experiment with PlexiGlas®.
Experiment 1 - Simulated Ocean Dive
Open the following online activity to simulate the light intensity experiment at various depths. The activity uses sliders to adjust the depth, and the darkness is automatically adjusted. This simulation can be used to gather data points, which can then be plotted and examined.
The simulation can be projected onto an overhead screen or television as a demonstration for students, or you can allow students to visit this page and experience the simulation themselves.
Experiment 2 - Layers of Plexiglas®
The following video shows a class of students collecting data indoors, using layers of Plexiglas to simulate water depth. Adding layers of Plexiglas decreases the light intensity in a manner similar to water.
Click here to view the transcript of the clip separately.
The goal of this experiment is to investigate how the intensity of light changes with depth. Have a steady light source such as the light from a window or from a flashlight. Connect a light sensor to a CBL. Do not connect the CBL to a graphing calculator. To take a reading press the mode button on the CBL. You should see the word "Sampling" flash on and off. When you are not taking a reading, press mode or ON to save power.
To model incremental depths, layers of tinted Plexiglas will be used to represent layers of water. Take a reading with no light on the sensor (cover the sensor with your hand). Take a second reading directly from the light source. Then, continually add layers of Plexiglas between the light source and the sensor. Record the depth and reading. (For this experiment, let the depth be equal to the number of layers of Plexiglas. For instance, if two layers of Plexiglas are used, record the depth as 2.)
Experiment 3 - Column of Water
The goal of this experiment is to investigate how the intensity of light changes with depth in water. Have students place a light source at the top of the tube. At the bottom of a tube, they should place a light sensor connected to a Calculator-Based Laboratory or other light sensing device.
Before recording any light intensity readings, allow students to choose a method that they will use to record the readings given by the CBL. They will need to decide what reading to record. Some possibilities are to note the maximum, minimum, average or most frequent reading.
Take a reading with no water in the tube and no light in the tube (cover the top). Take a reading with no water but with your light source. Then, add a fixed amount of water of your choosing. Repeat to gather readings until the top of the tube is reached. You will want to collect the data from about ten readings. Note that the light source may initially overwhelm the sensor. Therefore, the first few readings may be questionable.
After conducting each of the experiment(s), students should answer the questions in the Experiment packet. The following grapher can be used to explore possible functions to represent the data.
Based on the data and the graphs, conclude the lesson with a whole-class discussion about the nature of the function. Allow students to speculate as to the type of function that best models the data, and ask them to justify their conjectures.
