In the phenomenon of interference,energy.......

Four light sources produce the following four waves:
$(i)$ $y_1 = a \sin(\omega t + \phi_1)$
(ii) $y_2 = a \sin(2\omega t)$
(iii) $y_3 = d' \sin(\omega t + \phi_2)$
(iv) $y_4 = d' \sin(3\omega t + \phi)$
Superposition of which two waves gives rise to interference?

Consider the interference of two sources with intensities $I$ and $4I$. Find the intensity at a point where the phase difference is $\pi/2$. (in $I$)

If the wavelength of light is $4000 \, Å$, then the number of waves in a length of $1 \, mm$ will be:

Which property of light is responsible for interference?

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