Colored Shadows
Safety Warnings
Warning: Heat Caution
Purpose
Students observe that light travels in straight lines by blocking one of two colored light sources and predicting the resulting shadow colors. The demo builds from simple ray tracing to additive color mixing and can extend to pinhole camera image formation.
Figure 1:
Both lamps on with the circular barrier creating colored shadows: blue where red is blocked, orange where blue is blocked, and dark where both are blocked.
Figure 2:
Setup with room lights on: two labeled flood lamps, white board screen, circular disc barrier, and foam hand cutout.
Figure 3:
Only the blue lamp illuminated, showing uniform blue light on the screen.
Figure 4:
Only the red lamp illuminated, showing uniform red/orange light on the screen.
Figure 5:
Both lamps on: overlapping regions appear pink/magenta (blue + red), demonstrating additive color mixing.
Figure 6:
Circular barrier creates colored shadows: blue where red is blocked, orange where blue is blocked, dark center where both are blocked.
Figure 7:
Prediction slide: rays from two colored sources pass through a pinhole and form an inverted image. Students predict the image before seeing it.
Equipment
- 1
Demo Apparatus
- 1