Refraction Coin Trick

DCS Code: 6A42.40 Last Updated: March 27, 2026
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Purpose

Demonstrates refraction at a flat water-air interface. A coin hidden below the rim of a cup becomes visible when water is added, showing how Snell's law causes objects to appear shallower than their actual depth.

Stainless steel cup shown from the same camera angle: left view shows no coin visible, right view with water added shows the coin at the bottom
Figure 1: Before and after: from a fixed camera angle, the coin is hidden below the rim (left). After adding water (right), refraction at the water-air surface makes the coin visible.
Equipment