The phenomenon of interference is observed in .........

The total energy carried by a light wave when it travels from a rarer to a non-reflecting and non-absorbing medium:

Two light waves of intensities $I$ and $4I$ superpose at a point with a phase difference of $\pi / 2$. Calculate the resultant amplitude at that point.

The wave nature of light is confirmed because:

Two identical coherent sources are placed on a diameter of a circle of radius $R$ at a separation $x (x << R)$,symmetrically about the center of the circle. The sources emit waves of identical wavelength $\lambda$. Find the number of points on the circle with maximum intensity,given $x = 5 \lambda$.

Which property of light is responsible for interference?