Magic, Illusion or Trickery

Aim:To understand why we see red and blue when the only colours on the disc are black and white.

Question:Why do we see red and blue when the only colours on our disc are black and white?

Hypothesis:We think that when we spin the disk, the patterns on it might still look black and white.

Experiment - Equipment
• White paper
• Scissors
• Black vivid
• Cardboard
• Straight pin
• Pencil with an eraser.

Procedure:
1) Cut a circle four inches (10 cm) in diameter out of white paper.
2) Colour one half black.
3) Divide the white half into four equal parts.
4) In each segment draw three black arcs about ¾ inches (19 mm) thick.
5) Cut a circle four inches (10 cm) in diameter out of the cardboard.
6) Place the paper circle on the cardboard circle.
7) Mount them together on a pin, attach to a pencil with an eraser.
8) Revolve the disk at various speeds, clockwise and anti clockwise.

Observation:The arcs seem to close up to form 6 rings. At a slow speed, spinning clockwise, the outer rings look blue and the inner rings look red. When we spun them anti-clockwise, the colours reversed.

Conclusion:Our hypothesis was incorrect. We could see the arcs in red and blue.
The arcs seem to close to form rings, because the eye continues to see each arc for a short time after it has disappeared.

What actually happens is that we see red and blue when the only colours on the disc are black and white. The entire colour spectrum is present in white light, but our eyes register the different lengths of time.
When we spin the disk, light from the colours that make up white reach the eye, but are visible for only an instant before being followed by the black portions of the disk. Our eye is only able register a part of that colour spectrum-the blue, which has the shortest rays, and the red, which has the longest rays.