Fraunhofer lines are produced by the absorption of light in

Assertion: The colour of the green flower seen through red glass appears to be dark.
Reason: Red glass transmits only red light.

$A$ laser beam can be focused on an area equal to the square of its wavelength. $A$ $He-Ne$ laser radiates energy at the rate of $1 \, mW$ and its wavelength is $632.8 \, nm$. The intensity of the focused beam will be:

$A$ white screen illuminated by green and red light appears to be

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

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 $\lambda_0 = 6000 \text{ Å}$.