Problem 5.82

Diffused monochromatic light with wavelength $\lambda=0.60 \mu \mathrm{m}$ falls on a thin film with refractive index $n=1.5$. Determine the film thickness if the angular separation of neighbouring maxima observed in reflected light at the angles close to $\theta=45^{\circ}$ to the normal is equal to $\delta \theta=3.0^{\circ}$.