The wavelength associated with the electron moving in the first orbit of hydrogen atom with velocity $ 2.2 \times 10^6\, \text{m/s} $ is (in nm):(Given: $ m_e = 9.0 \times 10^{-31}\, \text{kg},\ h = 6.6 \times 10^{-34}\, \text{Js} $)
An electron in a hydrogen atom excites from $ n = 2 $ to $ n = 4 $. What is the change in angular momentum? (Planck's constant $ h = 6.64 \times 10^{-34} \, \text{J s} $)