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QPages 382-383: Q10: HC Verma: Concepts of Physics - Volume 2 Bohr's Model and Physics of the Atom Pages 382-383: Q10 Solution: An atom is in its excited state. Does the probability of its…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume that any incident radiation can trigger emission, but stimulated emission strictly requires the incident photon's energy to match the atomic transition energy ($\Delta E = h\nu$). You must distinguish this resonant condition from spontaneous emission, which is independent of the external radiation field.

An atom is in its excited state. Does the probability of its coming to ground state depend on whether the radiation is already present or not? If yes, does it also depend on the wavelength of the radiation present?

Step-by-Step Verified Solution

**Answer:** The probability of spontaneous emission does not depend on the presence of radiation. The probability of stimulated emission does depend on the presence of radiation of the correct wavelength. **Step-by-Step Explanation:** An excited atom can decay spontaneously by emitting a photon, regardless of whether radiation is present. This is spontaneous emission. If radiation of the correct frequency is already present, it can stimulate the atom to emit a photon in phase with the incident radiation. This is stimulated emission. Hence, the probability of coming to the ground state can depend on the presence of radiation (through stimulated emission), and it does depend on the wavelength of the radiation present (only radiation of the correct energy can stimulate emission) [citation:3].

All Questions in this Chapter

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