Question

Two mirrors of a laser separated by 8.0 cm form an optical cavity in which standing waves of laser light can be set up. Each standing wave has an integral number n of half wavelengths in the 8.0 cm length, where n is large and the waves differ slightly in wavelength. Near λ = 533 nm, determine the difference in wavelength between adjacent standing waves i.e., the least difference in wavelength between any two standing waves about that wavelength.

someone pls explain how to do this ;) no clue

Answer 1

L is about 533 nm
n (L1 / 2) = .08
(n+1) L2 / 2 = .08

n L1 = .16
(n+1) L2 = nL2 + L2 = .16
n(L1-L2) = L2
but L2 is about 533*10^-9 meters
n (L1-L2) = 533*10^-9
nL1 is about .16
n is about .08 / (533*10^-9 * 2) = 7.5*10^4
so
L1 - L2 = 533*10^-9 / 7.5*10^4