$A$ bulb of $40 \ W$ is producing light of wavelength $620 \ nm$ with $80 \%$ efficiency. The number of photons emitted by the bulb in $20 \ s$ is $(1 \ eV = 1.6 \times 10^{-19} \ J, hc = 12400 \ eV \ \mathring{A})$

The energy of the first (lowest) Balmer line of the $H$ atom is $x \ J$. The energy (in $J$) of the second Balmer line of the $H$ atom is:

Explain the phenomenon of black body radiation.

An electromagnetic radiation of wavelength $331.5 \ nm$ is made to strike the surface of a metal. Electrons are emitted with a kinetic energy of $1.2 \times 10^5 \ J \ mol^{-1}$. The work function (in $eV$) of the metal is (given: $h=6.63 \times 10^{-34} \ Js$,$N_{A}=6 \times 10^{23} \ mol^{-1}$,$1 \ eV = 1.6 \times 10^{-19} \ J$)?

The ratio of minimum wavelengths of Lyman and Balmer series will be $:-$

The energy of an electron in the second Bohr orbit of a hydrogen atom is: