Laser is/are:

The difference in the number of wavelengths,when yellow light propagates through air and vacuum columns of the same thickness,is one. Find the thickness of the air column. Given: Refractive index of air $\mu_a = 1.0003$,Wavelength of yellow light in vacuum $\lambda_0 = 6000 \text{ Å}$.

Statement $(S)$: Using Huygen's eye-piece,measurements can be taken but 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 option from the following:

According to the corpuscular theory of light,which of the following phenomena can be explained?

$A$ laser beam is used for carrying out surgery because it

Red light differs from blue light in its