Visible Light
Light, Sound and Waves

Snell’s window

Stories from Physics for 11-14 14-16 IOP RESOURCES

Anglers can hide themselves from their prey by exploiting a phenomenon arising from total internal reflection. When the surface of a pool of water is flat, a fish beneath the surface will observe the entire hemisphere above the water in a cone of angle 97°, a region known as Snell’s window or the optical man-hole. So if anglers position themselves at a low viewing angle relative to the surface of the water, their image is squashed and out of focus to the fish and they will remain undetected.


2023 IOP Awards

Teachers of Physics Awards

Recognising and celebrating outstanding contributions to the field of physics education.

Learn more