Using light from a monochromatic source to study diffraction in a single slit of width 0.1 mm, the lines width of central maxima is measured to be 5 mm on a screen held 50 cm away. The wavelength of light used is __________.
Fill in the blank with the correct answer from the options given below.

​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: