Wave Interference & Double-Slit – AP Physics 2 | ShowMeClass

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Wave Interference & Double-Slit

AP Physics 2 · Unit 6: Optics & Waves

Learning Objectives

Explain constructive & destructive interference

Derive double-slit maxima: d sinθ = mλ

Calculate fringe spacing: Δy = λL/d

Visualize path difference & interference pattern

Key Equations

Interference Rules

Constructive (bright): path diff = mλ (m = 0,1,2…)
Destructive (dark): path diff = (m+½)λ

Central max (m=0) is always brightest.
Smaller d → wider spacing.
Larger λ → wider spacing.

Colors

Wave from slit 1

Wave from slit 2

Superposition (sum)

Double-SlitInterferenceDiffractionAP Physics 2

λ =—

d =—

Δy =—

INTENSITY PATTERN ON SCREEN

Mode

Wavelength λ (nm) 550

Slit Separation d (μm) 50

Screen Distance L (m) 1.0

Number of Slits N 2

Display

Interference Analysis

📝 Quick Quiz▼

1. In a double-slit experiment, increasing λ will:

Decrease fringe spacing Increase fringe spacing Not change the pattern Eliminate the pattern

2. Destructive interference occurs when path difference is:

mλ (m + ½)λ 2mλ Zero

3. Decreasing slit separation d will:

Narrow the fringes Widen the fringes Remove the central max Make all fringes equal