एक हाइड्रोजन परमाणु में एक इलेक्ट्रॉन प्रथम उत्तेजित अवस्था (first excited state) से मूल अवस्था (ground state) में कूदता है। इलेक्ट्रॉन की गति में प्रतिशत परिवर्तन कितना होगा?

An α-particle having a kinetic energy of 7.7 MeV is approaching a fixed gold nucleus (atomic number Z = 79). Find the distance of closest approach.

A free electron of 2.6 eV energy collides with a H+ ion. This results in the formation of a hydrogen atom in the first excited state and a photon is released. Find the frequency of the emitted photon (take h = 6.6 × 10-34 J s).