Wave–Particle Duality and the Superposition Principle
Fire photons or electrons through a double slit one at a time and observe quantum interference building up. Toggle the which-path detector to destroy the fringes.
A. Source and geometry
With detector on, the coherent amplitude sum becomes an incoherent intensity sum — interference fringes disappear.
B. Fire particles and build the pattern
Top strip: each dot is one detected particle (accumulates). Bottom curve: exact theoretical probability distribution (not a fit). Each particle is sampled from this distribution individually — the pattern emerges statistically.
Observations
Record your measured data in the tables below. Refer to the lab manual for the full procedure.
Table 2.1 — Fringe spacing vs. slit separation (fixed λ, D)
| d (μm) | λD/d (μm) | Pattern notes |
|---|---|---|
Table 2.2 — Fringe spacing vs. wavelength / KE (fixed d, D)
| λ / KE setting | λ (nm) | Fringe spacing |
|---|---|---|
Table 2.3 — Which-path detector comparison (1000 particles each)
| Detector | Pattern description |
|---|---|
Rows: Off, On