The Shadow Illusion

Description:  Derek Muller from Veritasium uses the shadow illusion to show that the size and shape of a pinhole does not affect the image projected. Most of the participants believe they are looking at the shape of the hole rather than the shape of the Sun projected on the wall. This could be an excellent phenomenon to start a unit on light or vision.

Web Resource: Pinhole camera - Wikipedia

When sunlight shines through a small hole, it casts a circular image on the wall regardless of the shape of the hole. The size of the hole also doesn't affect the size of the image. This counterintuitive demonstration shows that the hole is acting like a pinhole camera, producing an image of the sun on the wall.