When light is incident normally on an air-glass interface, what percentage of light is reflected bac

Question

When light is incident normally on an air-glass interface, what percentage of light is reflected back, if the refractive index of the glass is 1,5 ?

Professor PC Thomas Classes · Answer

Reflectance $R = (\frac{n-1}{n+1})^2 = (\frac{0.5}{2.5})^2 = 4\%$.