The ground state energy of the hydrogen atom is -13.6 eV. If an electron makes a transition from an energy level -1.51 eV to -3.4 eV, calculate the wavelength of the spectral line emitted and name the series of hydrogen spectrum to which it belongs.

Write the application of x-rays.

For photo electronic effect in sodium, the figure shows the plot of cut-off voltage versus frequency of incident radiation. Calculate
(i) threshold frequency
(ii) work function for sodium.

Determine the value of the de Broglie wavelength associated with the electron orbiting in the ground state of hydrogen atom (Given En = -(13.6 n²) eV and Bohr radius r₀ = 0.53 Å). How will the de Broglie wavelength change when it is in the first excited state?

Write briefly the underlying principle used in Davison-Germer experiment to verify wave nature of electrons experimentally. What is the de-Broglie wavelength of an electron with kinetic energy (KE) 120 eV?