Question

What is the lifetime of an excited state in case of a metastable state?
(A) ${10^{ - 8}}\,s$
(B) ${10^{ - 3}}\,s$
(C) ${10^{ - 6}}\,s$
(D) ${10^{ - 12}}\,s$

Answer 1

Hint: In general, there are three states of an atom. They are ground state, metastable state, an excited state. Each state has different lifetimes. Usually, these three types of states are found in the laser energy level diagram. The energy of the laser moves from the ground state to the excited state.

Complete step by step answer:
In-ground state of an atom, the nucleus of an atom is surrounded by the electrons which occupy the shells, or orbitals of varying energy levels. The ground state of an electron, the energy level normally occupies the state of lowest energy for that electron. And there is a maximum energy that each electron will have and be the part of its atom. The atom in the ground state gets some energy and moves to the excited state.

In an excited state of an atom, the atom is temporarily present in this state. But the energy of the atom in an excited state is greater than the energy of an atom in an excited state. The atom gets extra energy by absorbing the photon or collides with the nearby atom. The lifetime of an atom in the excited state is ${10^{ - 7}}\,s$.

The metastable state is the state which lies between the ground state and excited state. The atom in the ground state absorbs some energy and goes to the excited state. From an excited state, it loses some energy and comes to a metastable state. The lifetime of the metastable state is ${10^{ - 3}}\,s$.

Hence, option (B) is correct.

Note:
In a three-level energy state, the material is first excited to a high energy level and then releases some energy and moves to a metastable state, then releases maximum energy and gets back to the ground state. The atom is continuously changing the states to produce some energy.