How many photons are required to provide $1 \, J$ of energy with a wavelength of $5000 \, \mathring{A}$?

$A$ photon of wavelength $4 \times 10^{-7} \, m$ strikes on a metal surface. The work function of the metal is $2.13 \, eV$. Calculate:
$(i)$ The energy of the photon in $eV$.
$(ii)$ The kinetic energy of the emission in $eV$.
$(iii)$ The velocity of the photoelectron in $ms^{-1}$ ($1 \, eV = 1.6020 \times 10^{-19} \, J$,mass of electron $m = 9.10939 \times 10^{-31} \, kg$).

Angular momentum of an electron in the second shell of a $Li^{+2}$ ion is:

Bohr's model can explain:

The energy required for the ionisation of a hydrogen atom is $13.6 \ eV$. What is the energy required for the ionisation of $He^+$ ion (in $eV$)?

What is the maximum wavelength line in the Lyman series of $He^{+}$ ion?