What is the path difference for destructive interference?

The light beams of intensities in the ratio of $9: 1$ are allowed to interfere. What will be the ratio of the intensities of maxima and minima?

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

Two coherent sources of wavelength $\lambda$ produce a steady interference pattern. The path difference corresponding to the $10^{\text{th}}$ order maximum will be:

Two identical light waves, propagating in the same direction, have a phase difference $\delta$. After they superpose, the intensity of the resulting wave will be proportional to

Two waves having intensities in the ratio $25 : 4$ produce interference. The ratio of the maximum to the minimum intensity is