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

Light from a point source falls on a small area placed perpendicular to the incident light. If the area is rotated about the incident light by an angle of $60^o$,by what fraction will the illuminance change?

Light from a sodium lamp is passed through cold sodium vapours. The spectrum of the transmitted light consists of:

Which colour of the light has the longest wavelength?

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

Statement $(S)$: Using Huygen's eye-piece, measurements can be taken, but they are not correct.
Reason $(R)$: The cross wires, scale, and final image are not magnified proportionately because the image of the object is magnified by two lenses, whereas the cross-wire scale is magnified by one lens only.
Identify the correct one of the following: