Two coherent sources of light interfere and produce fringe pattern on a screen. For central maximum, the phase difference between the two waves will be,

​A silicon monoxide ($$n$$​ = 1.45) film of 100 nm thickness is used to coat a glass camera lens ($$n$$​ = 1.56). What wavelength of light in the visible region will be most efficiently transmitted by this system?​

In a single slit diffraction experiment, light of wavelength 600 nm is used and the first minimum is observed at an angle of 30°. The width of the slit is:

The position of the image produced by a concave mirror when an object is placed at a distance such that light rays from the object are parallel to the principal axis is: