Activity Description

The following activity is similar to the the What if Anything is Wrong Task - Absorption by a Filter, except in this case the two filters are adjusted so that there is a slight overlap. The students are shown the following pictures of spectrum with the band that will be transmitted by each filter indicated. They are asked to predict the color transmitted by the combination of filters and explain their prediction. In the PowerPoint the prediction was asked for in a peer instruction format and then explanation was asked for following the prediction made after the small group discussion. The students are then showed the Color Vision Simulation from the PhET website with the filter turned off. The question is resolved by turning the filter on.

Transmission characteristics of the first filter

Transmission characteristics of the second filter

Target Conceptual Difficulty

Common misconception that filters add color to light instead of removing it.

PowerPoint

Predict and Explain Task - Transmission of Light by a Filter (TurningPoint)
Predict and Explain Task - Transmission of Light by a Filter (iClicker)

Simulation

http://phet.colorado.edu/en/simulation/color-vision

The simulation will start up with the RGB bulb tab showing. Click on the Single Bulb tab. Click on the monochromatic radio button on the right side of the screen and click the on the On/Off switch to turn off the filter. Adjust the sliders so that the bulb color is yellow and the filter color is just slightly to the orang of yellow. There should be a region of overlap in the spectra of the bulb and the filter.. At this point the simulation should look like the following figure, except the light will be yellow in color..

Presentation Notes

Once the simulation is set up, I ask the students to imagine that there is a yellow filter in front of the light bulb making the light yellow. Once the students have predicted the color of light transmitted by both filters, I turn on the yellow-orange filter to show the color of light transmitted by both.

Student Results

This activity taught me a very valuable lesson concerning asking questions about color. Where I had intended the adjective bright to indicate an intensity the students largely interpreted it as a shade of color. My intent was that the correct answer was yellow orange but most students interpreted the transmitted color as "bright yellow". Initially 68% gave this answer and following small group discussion, 95% of the students gave that as the correct answer. I learned this when presenting the simulation and causing significant consternation on the part of the students when I announced that the correct answer was yellow-orange. Notice that 68% of the students gave the correct reasoning for the answer while 32% still held the idea that the filters added color to the light..

1.) Predict what color light will be transmitted by both filters?
Responses(percent) (count)
None 0% 0
Bright yellow 68.42% 13
Yellow orange 21.05% 4
Orange 0% 0
White 10.53% 2
Totals 100% 19


2.) Predict what color light will be transmitted by both filters?
Responses(percent) (count)
None 0% 0
Bright yellow 94.74% 18
Yellow orange 5.26% 1
Orange 0% 0
White 0% 0
Totals 100% 19


3.) Explain your reasoning.
Responses(percent) (count)
The filters absorb different colors of light so all of the light is absorbed 0% 0
Light form the part of the curves that overlap will be transmitted 68.42% 13
The light from the filters will add together 31.58% 6
Some other reason 0% 0
Totals 100% 19

Pen and Paper Actvivities

Pen and Paper version of this activty

Follow up tipers from homework assignments, test reviews and test items