Predict whether reflected ray X undergoes a phase change.

state, in terms of d, the path difference between the reflected rays X and Y.

calculate the smallest value of d that will result in destructive interference between ray X and ray Y.

discuss a practical advantage of this arrangement.

Draw, on the axes, the variation with diffraction angle of the intensity of light incident on the retina of the observer.

Estimate, in rad, the smallest angular separation of two distinct point sources of light of wavelength 656 nm that can be resolved by the eye of this observer.

there is a phase change ✔
of $\mathrm{\pi }$ OR as it is reflected off a medium of higher refractive index ✔

2d ✔
NOTE: Accept 2dn

$2dn=\frac{\lambda }{2}$ ✔

$d=«\frac{\lambda }{4n}=\frac{656}{4\times 1.38}=» 119 «\mathrm{nm}»$ ✔

NOTE: Award [2] for bald correct answer

reflection from «front surface of» lens eliminated/reduced
OR
energy reaching sensor increased ✔

at one wavelength ✔

NOTE: Accept reference to reduction of glare for MP1

standard single slit diffraction pattern with correct overall shape ✔

secondary maxima of right size ✔

NOTE: Secondary maximum not to exceed 1/5^th of maximum intensity

Ignore width of maxima

use of $\theta =\frac{1.22\lambda }{b}$✔

$\theta =2.9\times {10}^{-4}$ «rad» ✔

NOTE: Award [2] for bald correct answer