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QPages 382-383: Q4: HC Verma: Concepts of Physics - Volume 2 Bohr's Model and Physics of the Atom Pages 382-383: Q4 Solution: When white radiation is passed through a sample of hydrogen gas …

When white radiation is passed through a sample of hydrogen gas at room temperature, absorption lines are observed in Lyman series only. Explain.

Step-by-Step Verified Solution

**Answer:** Because at room temperature, almost all hydrogen atoms are in the ground state (n = 1). Absorption can only occur from n = 1 to higher levels, which corresponds to the Lyman series. **Step-by-Step Explanation:** The energy difference between n = 1 and n = 2 is 10.2 eV, which corresponds to a photon of wavelength 121.6 nm (ultraviolet). At room temperature, thermal energy (~0.025 eV) is much less than 10.2 eV, so atoms cannot be excited to n = 2 by collisions. Hence, they remain in the ground state. Absorption lines are observed only for transitions starting from n = 1, i.e., the Lyman series [citation:8].

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