Which optical phenomena can be explained by the wave nature of light?

The phenomenon of interference is exhibited by:

Two plane polarized light waves combine at a certain point whose electric field components are $E_1 = E_0 \sin(\omega t)$ and $E_2 = E_0 \sin(\omega t + \frac{\pi}{3})$. Find the amplitude of the resultant wave.

Interference cannot be observed in two sodium lamps of equal power because the two waves do not have a .....

Light waves producing interference have their amplitudes in the ratio $3: 2$. The intensity ratio of maximum and minimum of interference fringes is

Two light waves of intensities $I$ and $2I$ superimpose on each other. If the path difference between the light waves reaching a point is $12.5 \%$ of the wavelength of the light,then the resultant intensity at the point is (Both the light waves have same wavelength).