Question

An electron makes a transition from an excited state to the ground state of a hydrogen like atom / ion. During this transition of the electron, its 

(1) kinetic energy; potential energy and total energy all decrease 

(2) kinetic energy decreases, potential energy increases and total energy remains same 

(3) kinetic energy and total energy decrease but potential energy increases 

(4) kinetic energy increases, but potential energy and total energy both decrease 

Answer 1

Correct option : (4)

Explanation :

In the given transition, principal quantum number (n) decreases. Now the speed of the electron in the nth orbit, (v_n), is inversely proportional to n. Hence, when n decreases, v_n and, therefore, the kinetic energy of the electron, increases. We also know 

Total energy = – K.E and 

Potential energy = –2 K.E 

Due to –ve sign, in the expression for T.E and P.E; both these energies decrease when n decreases.