PHYS 1407 – Conceptual Physics II

Introduction

In this activity we will investigate the addition of colors both in pigments and with colored lights.

Procedure

Part 1 Absorption and Reflection of Light

Put about 8 layers of thickness of red cellophane over the end of the flashlight. Hold the cellophane on the end with a rubber band.

Q1) Shine the light on the piece of paper. What color does it appear?

Now hold about 8 thicknesses of green cellophane in front of the red. Shine the light on the paper now.

Q2) What did you observe?

Now hold about 8 thicknesses of blue cellophane in front of the red and shine the light on the paper.

Q3) What did you observe?

Replace the red cellophane with 8 layers of the green.

Q4) Shine the light on the piece of paper. What color does it appear?

Now hold about 8 thicknesses of red cellophane in front of the green. Shine the light on the paper now.

Q5) What did you observe?

Now hold about 8 thicknesses of blue cellophane in front of the green and shine the light on the paper.

Q6) What did you observe?

Replace the green cellophane with 8 layers of the blue.

Q7) Shine the light on the piece of paper. What color does it appear?

Now hold about 8 thicknesses of red cellophane in front of the blue. Shine the light on the paper now.

Q8) What did you observe?

Now hold about 8 thicknesses of green cellophane in front of the blue and shine the light on the paper.

Q9) What did you observe?

Q10) Does passing light through the cellophane add color to the light or remove color from the light? Support your answer with the sequence of observations you just made.

Replace the blue cellophane with 8 layers of red again. Shine the dimmer outer part of the flashlight’s beam on the piece of red foam.

Q11) Describe what you see.

Now shine the dimmer outer part on the piece of green foam.

Q12) Describe what you see.

Replace the red cellophane with green and repeat your series of observations by shining the dimmer outer edge of the beam on the green, red and blue pieces of foam.

Q13) Summarize your observations.

Replace the green cellophane with blue and repeat your series of observations by shining the dimmer outer edge of the beam on the blue, red and green pieces of foam.

Q14) Summarize your observations.

Q15) Which colors of foam seemed to reflect red light?

Q16) Which colors of foam seemed to absorb red light?

Q17) Which colors of foam seemed to reflect green light?

Q18) Which colors of foam seemed to absorb green light?

Q19) Which colors of foam seemed to reflect blue light?

Q20) Which colors of foam seemed to absorb blue light?

Q21) Do the pieces of foam obtain their color from the light reflected by them or the light absorbed by them?

P22) If you shine the flashlight without cellophane on the red piece of foam, predict how it will appear if you view it through the red cellophane.

P23) Repeat with the green cellophane.

P24) Repeat with the blue cellophane.

Test each of your predictions.

Q25) Were you correct? Itemize your answers as necessary.

P26) Make a similar set of predictions for viewing the blue foam through the various colors of cellophane.

Test your predictions.

Q27) Were you correct. Itemize as necessary.

P28) Make a similar set of predictions for viewing the green foam through the various colors of cellophane.

Test your predictions.

Q29) Were you correct. Itemize as necessary.

Q30) Explain why you observed that the foam appeared its actual color when viewed through the same color cellophane but black (or close to) when viewed through a different color of cellophane.

Part 2 Addition of Light

You will need to coordinate with two other groups for this activity. Place 8 layers of red cellophane over one group’s flashlight, 8 layers of green over another and 8 layers of blue over the third.

Shine the red and green flashlights so that they overlap on a piece of white paper.

Q32) What color appears where they overlap?

Shine the red and blue flashlights so that they overlap on a piece of white paper.

Q33) What color appears where they overlap?

Shine the blue and green flashlights so that they overlap on a piece of white paper.

Q34) What color appears where they overlap?

Shine all three flashlights so that they overlap on a piece of white paper.

Q35) What color appears where they overlap?

Note it can be a little difficult to see these colors. We can do this in a much more controlled fashion using a computer simulation.

Boot the laptop. The user id is student and the space for the password is left blank. Start Internet Explorer and go to the website phet.colorado.edu Click on box Go to the Simulations. In the frame on the left click on Light and Radiation. Then scroll down and launch the simulation called Color Vision and Filters. The simulation is fairly self explanatory. Try adding each of the different color combinations you did above and see what you get.

Q36) Summarize your results with the simulation.

Summary Questions

S37) A solid object appears a certain color because of the light ___________ from it.

S38) Red and green light added together make _____ light.

S39) Red and blue light added together make _____ light.

S40) Green and blue light added together make ____ light.

S41) Red, green, and blue light added together would make ______ light.

S42) What would yellow and blue light added together make?

S43) What would magenta (light purple) and green light added together make?

S44) What would cyan (light blue green) and red light added together make?