Variable Double Slit - Physics Demonstrations - Variable Double Slit | Physics Undergraduate Labs

Use only Class 2 or Class 3R lasers (<5 mW) for classroom demonstrations. Never point the laser at students or allow direct eye exposure. The green laser provides excellent visibility at safe power levels. Instruct students not to look directly into the beam.

Purpose

Demonstrates double-slit interference with variable slit separation using a laser and PASCO diffraction wheel. Students observe the inverse relationship between slit separation and fringe spacing, providing direct verification of $\Delta y = \lambda L / d$ .

$Green laser and PASCO diffraction wheel mounted on optical rail with optical sliders, projecting a faint green interference pattern onto white paper magneted to blackboard$

$Close-up of PASCO High Precision Diffraction Slits wheel showing sections for Double Slits, Variable Double Slit (d = 0.125 to 0.75 mm), Multiple Slits, and Comparisons$

Figure 1: Green laser and diffraction wheel on optical rail, with interference pattern projected onto white paper on the blackboard.

Figure 2: PASCO diffraction wheel with sections for double slits, variable double slit (d = 0.125 to 0.75 mm), multiple slits, and comparisons.

Optical Slider

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Safety Warnings

Warning: Laser Safety

Purpose