The relative luminosity of wavelength $600 \,nm$ is $0.6$. Find the radiant flux of $600 \,nm$ needed to produce the same brightness sensation as produced by $120 \,W$ of radiant flux at $555 \,nm$.

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

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:

Fraunhofer lines are produced by the absorption of light in

Compare and contrast the interference and diffraction.

Which colour of the light has the longest wavelength?