Question
Explain emission lines and absorption lines.
✓
Answer
→According to the third postulate of Bohr's model, when an atom makes a transition from the higher energy state with quantum number $n_{ i }$ to the lower energy state with quantum number $n_f\left(n_f<n_i\right)$, the difference of energy is carried away by a photon of frequency $V_{i f}$ such that $h V_{i_f}= E _{n_i}- E _{n_f}$
→Since both $n_f$ and $n _i$ are integers, this shows that in transitions between different atomic levels, light is radiated in various discrete frequencies.
→The various lines in the atomic spectra are produced when electrons jump from higher energy state to a lower energy state and photons are emitted. These spectral lines are called emission lines.
→On the other hand, when an atom absorbs a photon that has the same energy needed by the electron in a lower energy state to make transitions to a higher energy state, the process is called absorption.
→Thus, if photons with a continuous range of frequencies pass through a rarefied gas and then are analysed with a spectrometer, a series of dark spectral absorption lines appear in the continuous spectrum. The dark lines indicate the frequencies that have been absorbed by the atoms of the gas.
→Since both $n_f$ and $n _i$ are integers, this shows that in transitions between different atomic levels, light is radiated in various discrete frequencies.
→The various lines in the atomic spectra are produced when electrons jump from higher energy state to a lower energy state and photons are emitted. These spectral lines are called emission lines.
→On the other hand, when an atom absorbs a photon that has the same energy needed by the electron in a lower energy state to make transitions to a higher energy state, the process is called absorption.
→Thus, if photons with a continuous range of frequencies pass through a rarefied gas and then are analysed with a spectrometer, a series of dark spectral absorption lines appear in the continuous spectrum. The dark lines indicate the frequencies that have been absorbed by the atoms of the gas.
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