A convex lens of diameter 8.0 cm is used to focus a parallel beam of light of wavelength 620 nm. If the light be focused at a distance of 20 cm from the lens, what would be the radius of the central bright spot formed?

A parallel beam of white light is incident normally on a water film 1.0 × 10^-4 cm thick. Find the wavelength in the visible range 1400 nm-700 nm) which are strongly transmitted by the film. Refractive index of water = 133.

A glass surface is coated by an oil film of uniform thickness 1.00 × 10^-4 cm. The index of refraction of the oil is 1.25 and that of the glass is 1.50. Find the wavelengths of light in the visible region (400 nm-750 nm) which are completely transmitted by the oil film under normal incidence.

Plane microwaves are incident on a long slit having a width of 5.0 cm. Calculate the wavelength of the microwaves if the first diffraction minimum is formed at θ = 30^o.

Light of wavelength 560 nm goes through a pinhole of diameter 0.20 mm and falls on a wall at a distance of 200 m. What will be the radius of the central bright spot formed on the wall?