What is the frequency of the light emitted from a sodium lamp?

What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room,its intensity essentially remains constant. What geometrical characteristic of $LASER$ beam is responsible for the constant intensity which is missing in the case of light from the bulb?

$A$ circular disc of which $2/3$ part is coated with yellow and $1/3$ part is with blue. It is rotated about its central axis with high velocity,then it will be seen as

$A$ source of light emits a continuous stream of light energy which falls on a given area. Luminous intensity is defined as

Mention the colours which have the least and the most wavelength in visible light.

Properly arrange the effects with their reasons:

Effects	Reasons
$(i)$ Rainbow formation	$(a)$ Reflection
$(ii)$ Red colour of danger signals	$(b)$ Scattering
$(iii)$ Different colours of thin oil film and soap bubbles	$(c)$ Chromatic aberration
$(iv)$ Coloured images formed by lenses	$(d)$ Dispersion
$(v)$ Different colours of clouds	$(e)$ Interference