A circular acrylic water tank with a clear front has a white back with a printed protractor. A pivoting arm attached to the back plate can be rotated 360° around the tank and carries a magnetically mounted diode laser with a built-in beam spreader.
The tank is half-filled with water, and a bright, narrow ray is directed onto the water surface from above or below to measure the incident and refracted angles.
The critical angle and total internal reflection can also be clearly demonstrated.
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