Ncert Exercises & Solutions

A set of atoms in an excited state decays

1.	in general to any of the states with lower energy
2.	into a lower state only when excited by an external electric field
3.	all together simultaneously into a lower state
4.	to emit photons only when they collide

(1) Hint: The decay can occur in different ways.

A set of atoms in an excited state decays in general to any of the states with lower energy.