Mnemonic 1 — Fringe width: "Beta = Lambda D over d" $\beta = \lambda D/d$ To increase $\beta$: "Larger $\lambda$, Larger $D$, Less $d$" (Three L's)

Mnemonic 2 — Bright vs Dark: "Bright is Whole, Dark is Half-Odd"

• Bright: $\Delta = n\lambda$ (whole wavelengths)
• Dark: $\Delta = (n-\frac{1}{2})\lambda$ (half-odd wavelengths)

Mnemonic 3 — Brewster: "Brewster = Bend at 90" At Brewster's angle, reflected ⊥ refracted. Formula: $\tan\theta_p = n$.

Mnemonic 4 — Single slit minima: "$a\sin\theta = n\lambda$" for MINIMA (opposite of YDSE where same form gives MAXIMA).

Mnemonic 5 — Three polaroids: "Half → Half → Half = One-eighth" $I_0 \xrightarrow{/2} I_0/2 \xrightarrow{\cos^2 45°} I_0/4 \xrightarrow{\cos^2 45°} I_0/8$

Mnemonic 6 — Medium effect: "Wavelength shrinks in water, so fringes shrink" $n = 4/3$ (water) → $\beta' = 3\beta/4$