Cornell Plate Single-Slit Diffraction - Physics Demonstrations - Cornell Plate Single-Slit Diffraction | Physics Undergraduate Labs

Use only Class 2 or Class 3R lasers (< 5 mW) for classroom demonstrations. Never look directly into the laser beam or its specular reflections. Ensure the beam path is above or below eye level of seated students. The polished steel plate can create strong reflections—the construction-paper shield helps minimize this hazard. Brief the class on laser safety before beginning.

Purpose

Demonstrates single-slit Fraunhofer diffraction using a Cornell plate with calibrated slits of varying widths. Students observe the inverse relationship between slit width and diffraction pattern width, with quantitative verification possible using known slit dimensions.

$Green laser and Cornell diffraction plate mounted on optical rail, with single-slit diffraction pattern projected on white paper attached magnetically to the blackboard$

Cornell plate calibration chart with three sections: single slits of varying width (bottom), parallel slits of varying width (middle), and variable spacing at constant width (top), with slit widths from 0.033 mm to 1.40 mm

$Four green single-slit diffraction patterns stacked vertically, showing progressively wider central maxima and more visible side lobes as slit width decreases$

Figure 1: Green laser illuminates the Cornell plate on an optical rail, projecting a single-slit diffraction pattern onto paper magnetically attached to the blackboard.

Figure 2: Cornell plate calibration chart. The bottom rows are single slits with varying widths (0.033–1.40 mm); middle rows are parallel slits with varying width; top rows have variable spacing at constant width.

Figure 3: Diffraction patterns from four different slit widths. Narrower slits produce wider patterns with more visible side lobes, demonstrating the inverse relationship $W \propto 1/a$.

Optical Slider

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Polished Steel Plate

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Safety Warnings

Warning: Laser Safety

Purpose