If the wavelength of light is $4000 \text{ Å}$, then the number of waves in $1 \text{ mm}$ length will be . . . . . . -

In an interference pattern obtained by two coherent sources,the variation in intensity is $5\%$ of the average intensity. Find the ratio of the intensities of the two sources.

The figure shows two point sources which emit light of wavelength $\lambda$ in phase with each other and are at a distance $d = 5.5 \lambda$ apart along a line which is perpendicular to a large screen at a distance $L$ from the center of the sources. Assume that $d$ is much less than $L$. Which of the following statement$(s)$ is (are) correct?

In the interference of two coherent sources of different intensities,the ratio of maximum and minimum intensity is $\frac{I_{\max}}{I_{\min}} = \frac{144}{81}$. What is the ratio of their amplitudes?

The ratio of intensities of two waves producing interference is $9: 4$. The ratio of the resultant maximum and minimum intensities will be:

When two light waves of equal intensity superimpose,the maximum intensity obtained is $I$. If the intensity of one of the waves is quadrupled,then the maximum intensity obtained is