Rotating Mirror beside Water Tank
Safety Warnings
Warning: Laser Safety - Class 3R Device
Warning: Silver Nitrate Handling
Purpose
Students observe total internal reflection at a water-air interface by sweeping a laser beam through a range of incident angles. The reflected beam visibly brightens as the angle approaches critical, and the refracted beam disappears beyond it.
Figure 1:
Complete experimental setup showing the laser, rotating mirror mount, and water tank. The green laser beam is visible entering the water and both reflecting and refracting at the water-air interface.
Figure 2:
Laser beam at an angle below the critical angle, showing both transmitted (refracted) and reflected components at the water-air interface.
Figure 3:
Beam approaching the critical angle with increasingly intense reflection back into the water. The incident and reflected beams are clearly visible due to scattering from non-dairy creamer and fog particles.
Figure 4:
Near-critical angle configuration where the reflected beam is very bright and the refracted beam is becoming progressively dimmer and closer to the interface.
Figure 5:
Configuration very close to or at the critical angle, demonstrating strong reflection back into the water with minimal or no transmission into the air above.
Equipment
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Demo Apparatus
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