Water Light Pipe - Physics Demonstrations - Water Light Pipe | Physics Undergraduate Labs

The laser can cause permanent retinal damage. Never aim it toward students, even when the stopper is blocking it. Turn it off immediately after adjusting and when the demo is over.

Purpose

A laser beam follows a curved stream of water flowing from a tank, trapped by total internal reflection at the water-air boundary. A striking visual analogy for fiber optics — light follows the curve of the medium, not a straight line through air.

Green laser beam trapped inside a curved stream of water flowing from an acrylic tank, with bright reflection points visible along the stream's parabolic arc against a dark background

Full setup: laser on a green metal stand at left, clear acrylic tank filled with water on black metal stands at right, green laser beam visible as a horizontal line in the water, with power supply on the floor below

Figure 1: The laser beam follows the water stream by total internal reflection. Bright spots mark where the beam bounces off the water-air interface.

Figure 2: Complete setup: laser mounted on stand at left, water tank on stands at right. The green beam is visible in the water due to suspended non-dairy creamer particles.

Spare Tank Plug

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Creamer Dispensing Shaker

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Plastic Tank without Lid

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Bucket with String

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Water Light Pipe Tank

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Water Light Pipe Frame

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Safety Warnings

Danger: Laser Eye Hazard

Purpose