Real Double-Slit Fringe Ledger

Double-Slit Fringe Intensity Really Dips and Recovers

A real physim double-slit interference simulation (scenario examples/double-slit-interference-2d-young.json) supplies every value on this page, each rounded to four decimal places from the measured screen field after it settles — this is not the idealized smooth-falloff picture. Moving away from the screen's bright center, the real relative intensity genuinely dips into an interference dark band, then climbs back up farther out even though that row sits farther from the center than the dip — a real double-slit fringe pattern rises and falls as the two path lengths trade whole and half wavelengths, it does not fade away smoothly. Real double-slit setups add finite slit width, coherence length, and detector noise beyond this ideal two-source model.

Every value in this lesson is rounded to four decimal places from a real physim double-slit-interference-2d numerical simulation (scenario examples/double-slit-interference-2d-young.json), not derived from a closed form. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

The real fringe intensity dips well below the center

A real physim double-slit run measures a relative intensity of 0.7071 at the screen's center, y = 4.0000 metres. Moving out to y = 3.2667 metres, the real intensity really drops to 0.2307 of the central value — a genuine interference dark band, not a smooth falloff.

IIc(ya)=0.7071 → IIc(yb)=0.2307\frac{I}{I_c}(y_a)=0.7071\ \to\ \frac{I}{I_c}(y_b)=0.2307
Real double-slit fringe: center to dipGhost trail traces the real relative-intensity curve; the ledger cites the center and dip rows.y=4.0000 m I/Ic=0.7071 (center)y=3.2667 m I/Ic=0.2307 (dip)

The real fringe intensity recovers farther out

Moving out even farther, to y = 2.4667 metres, the real intensity climbs back up to 0.6519 of the central value — brighter than the closer dip at y = 3.2667 metres, even though this row is farther from the center. Real double-slit intensity does not fall off monotonically with distance; it rises and falls as the two real path lengths trade whole and half wavelengths.

IIc(yc)=0.6519 > IIc(yb)=0.2307\frac{I}{I_c}(y_c)=0.6519\ >\ \frac{I}{I_c}(y_b)=0.2307
Real double-slit fringe: dip to recoveryThe same trail; the ledger adds the recovery row.y=4.0000 m I/Ic=0.7071 (center)y=3.2667 m I/Ic=0.2307 (dip)y=2.4667 m I/Ic=0.6519 (recovery)