When light emitted by a white hot solid is passed through a sodium flame,the spectrum of the emergent light will show

$A$ beam of ultraviolet light of all wavelengths passes through hydrogen gas at room temperature,in the $x-$ direction. Assume that all photons emitted due to electron transition inside the gas emerge in the $y-$ direction. Let $A$ and $B$ denote the lights emerging from the gas in the $x$ and $y$ directions respectively.

In a $He-Ne$ laser,the metastable state exists in:

An electron of a stationary Hydrogen atom transitions from the fifth energy level to the ground level. The velocity that the atom acquires as a result of photon emission is ( $m=$ mass of the atom,$R=$ Rydberg's constant,$h=$ Planck's constant).

During a total solar eclipse,the Fraunhofer lines become clearly visible because...

The wavelength of the emission line spectrum and the absorption line spectrum of a substance are related as: