Activity Description

The following statement is presented to the students: "A student is holding a red and a green filter in front of a bright white light. The light passes through the red filter first. She states:'If I look through the red and green filter at the same time, I will see yellow light since red and green light add together to make yellow light.'" The students are then showed the Color Vision Simulation from the PhET website with the red filter turned off. Students answer if anything is wrong with the simulation. The question is resolved by turning the red filter on.

Target Conceptual Difficulty

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

PowerPoint

What if Anything is Wrong Task - Absorption of Light by a Filter (TurningPoint)

What if Anything is Wrong Task - Absorption 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 green and the filter color is red. At this point the simulation should look like the following figure.

Presentation Notes

Once the simulation is set up, I ask the students to imagine that there is a green filter in front of the light bulb making the light green. Once the students have answered whether or not there is anything wrong with the statement, I turn on the red filter to demonstrate that no light passes through both filters.

Student Results

This question was posed in a Peer Instruction format. The students answered the question on their own with only 32% giving the correct answer that no light is passed by the combination of filters. The most common answer was that the light would be red wiht 58% of the students giving that response.

1.) What if anything is wrong with the student's statement?
Responses (percent) (count)
Nothing the statement is fine 10.53% 2
If you mix red and green paint you get brown not yellow 0% 0
The light will be red since the green was absorbed by the red filter 57.89% 11
The light will be green since it passes through the green filter last 0% 0
No light will pass through that combination of filters. 31.58% 6
Totals 100% 19

Following group discussion many students changed their answers and the most common answer became that no light passed through both filters with 68% of the students answering that. the second most common answer following group discussion was the light would be red, definitiely suggesting that the student hold an idea that a filter changes the color of light to the same as the filter.

2.) What if anything is wrong with the student's statement?
Responses(percent) (count)
Nothing the statement is fine 0% 0
If you mix red and green paint you get brown not yellow 0% 0
The light will be red since the green was absorbed by the red filter 31.58% 6
The light will be green since it passes through the green filter last 0% 0
No light will pass through that combination of filters. 68.42% 13
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