Which colour of the light has the longest wavelength?

Match Column-$1$ with Column-$2$ when a wave propagating in a denser medium enters a rarer medium:

Column-$1$	Column-$2$
$(a)$ Speed	$(i)$ Increases
$(b)$ Its amplitude	$(ii)$ Decreases
	$(iii)$ Remains constant

Compare and contrast the interference and diffraction.

Red light differs from blue light as they have :

$A$ zone plate of focal length $60\,cm$ behaves as a convex lens. If the wavelength of incident light is $6000\,\mathring{A},$ then the radius of the first half-period zone will be:

The maximum illumination on a screen at a distance of $2\, m$ from a lamp is $25\, lux.$ The value of total luminous flux emitted by the lamp is