Calculate the energy associated with third orbit of $\mathrm{He}^{+}$.

What is the wavenumber of the photon emitted during transition from the orbit $\mathrm{n}=5$ to that of $\mathrm{n}=2$ in hydrogen atom? $\left[\mathrm{R}_{\mathrm{H}}=109677 \mathrm{~cm}^{-1}\right]$

What is de Broglie's wavelength for a particle having mass $6.64 \times 10^{-27} \mathrm{~kg}$ moving with velocity of $3 \times 10^3 \mathrm{~ms}^{-1} ?\left[\mathrm{~h}=6.63 \times 10^{-34} \mathrm{Js}\right]$