In Figure a, the waves along rays 1 and 2 are initially in phase, with the same wavelength ? in air. ?Ray 2 goes through a material with length L and index of refraction n. The rays are then reflected by mirrors to a common point P on a screen. Suppose that we can vary L from 0 to 2400 nm. Suppose also that, from L = 0 to L_s = 900nmi, the intensity I of the light at point P varies with L as given in Figure. At what values of L greater than L, is intensity I

(a) Maximum and

(b) Zero?

(c) What multiple of i gives the phase difference between ray 1 and ray 2 at common point P when L = 1200nm?

L (nm) Screen Ray 2 Ray 1 (a) (b)