If the wavelength of an electromagnetic radiation is $2000 \ \text{Å}$,what is its energy in ergs?

Two series of spectral lines of atomic hydrogen which do not belong to the infrared spectral region are

The threshold frequency of a metal is $10^{15} \ s^{-1}$. The ratio of maximum kinetic energies of the photoelectrons,when the metal is irradiated with radiations of frequencies $1.5 \times 10^{15} \ s^{-1}$ and $2.0 \times 10^{15} \ s^{-1}$ respectively,is

Assertion : Angular momentum of an electron in any orbit is given by angular momentum $= \frac{nh}{2\pi}$,where $n$ is the principal quantum number.
Reason : The principal quantum number,$n$,can have any integral value.

What is the ratio of the wave number of the first line (lowest energy line) of the Balmer series of the $H$ atomic spectrum to the first line of its Brackett series?

In an electron transition from an infinite state to the ground state in an $H$ atom,find the emitted wavelength. (in $nm$)