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

Green lasers used in teaching demonstrations are typically Class 2 (<1 mW) or Class 3R (1-5 mW). Never look directly into the laser beam or view specular reflections. Brief accidental exposure causes blink response, but deliberate staring can cause eye damage. Ensure the beam terminates on the screen and does not reflect toward the audience. Warn students not to stare at the laser aperture.

Purpose

Demonstrates single-slit Fraunhofer diffraction and the inverse relationship between slit width and angular spread. Students directly observe that narrower slits produce wider diffraction patterns by rotating through discrete slits from 0.02 to 0.16 mm.

$Green laser and PASCO diffraction wheel mounted on optical rail sliders, projecting a single-slit diffraction pattern onto white paper attached to the blackboard$

$Close-up of PASCO High Precision Diffraction Slits wheel showing single slits (0.02–0.16 mm), variable slit (0.02–0.20 mm), circular apertures, and pattern options$

Figure 1: Setup showing the green laser and diffraction wheel on an optical rail, with the diffraction pattern projected onto white paper magneted to the blackboard.

Figure 2: PASCO diffraction wheel with discrete single slits (0.02, 0.04, 0.08, 0.16 mm), a variable slit (0.02–0.20 mm), circular apertures, and assorted diffraction patterns.

Optical Slider

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Single-Slits Wheel

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Safety Warnings

Warning: Laser Safety - Class 2 or 3R

Purpose