If the ratio of maximum and minimum intensities is $36 : 1$ in an interference pattern,then the ratio of amplitudes of the interfering waves is

Two coherent sources $S_1$ and $S_2$ and a screen are arranged as shown in the figure. If the distance between the two coherent sources is $n \lambda$ and the distance of the screen from the nearer coherent source $S_2$ is $D$,then the distance of the first bright fringe on the screen from the point $O$ is (where $\lambda$ is the wavelength of the light emitted by the coherent sources).

Two identical light waves having phase difference $\phi$ propagate in the same direction. When they superpose,the intensity of the resultant wave is proportional to

If the wavelength of light is $4000 \mathring A$,then the number of waves in $1 \ mm$ length will be

Two sources are said to be coherent if they produce waves

Radio waves coming at an angle $\alpha$ to the vertical are received by a radar after reflection from a nearby water surface and directly. What should be the height of the antenna from the water surface so that it records a maximum intensity? (wavelength $= \lambda$)