Concepts Of Physics MCQ Edition [Volume 2]
- Exam
- Concepts Of Physics MCQ Edition [Volume 2]
- Subject
- Physics
- Chapter
- Bohr's Model and Physics of the Atom
Concepts Of Physics MCQ Edition [Volume 2] · Physics · Bohr's Model and Physics of the Atom
During a laboratory experiment involving emission from atomic...
During a laboratory experiment involving emission from atomic hydrogen in a discharge tube, only a small number of lines are observed, while the hydrogen spectrum of a star exhibits a large number of lines. This occurs because in a laboratory
Options
- Athe quantity of hydrogen used is much smaller than the amount present in the star
- Bthe gravitational pull is much weaker than that in the star
- Cthe pressure of the hydrogen is much lower than that of the star
- Dthe temperature of the hydrogen is much lower than that of the star
Correct answer
D. the temperature of the hydrogen is much lower than that of the star
Step-by-step solution
The number of spectral lines observed in an emission spectrum depends on the number of atoms undergoing transitions from various excited energy levels.
In a star, the temperature is extremely high. This high thermal energy excites a significant fraction of hydrogen atoms to higher principal quantum numbers. In contrast, the temperature in a laboratory discharge tube is much lower, meaning fewer atoms reach these highly excited states.
Furthermore, the total quantity of hydrogen in a star is astronomically larger than the amount present in a laboratory setup. Even if the probability of an atom occupying a highly excited state is small, the massive total number of atoms in a star ensures that the absolute number of transitions is large enough to produce detectable spectral lines. In the laboratory, the small quantity of hydrogen limits the observability of transitions from higher energy levels.
Thus, both the smaller quantity and the lower temperature of hydrogen in the laboratory account for the fewer observed spectral lines.
In a star, the temperature is extremely high. This high thermal energy excites a significant fraction of hydrogen atoms to higher principal quantum numbers. In contrast, the temperature in a laboratory discharge tube is much lower, meaning fewer atoms reach these highly excited states.
Furthermore, the total quantity of hydrogen in a star is astronomically larger than the amount present in a laboratory setup. Even if the probability of an atom occupying a highly excited state is small, the massive total number of atoms in a star ensures that the absolute number of transitions is large enough to produce detectable spectral lines. In the laboratory, the small quantity of hydrogen limits the observability of transitions from higher energy levels.
Thus, both the smaller quantity and the lower temperature of hydrogen in the laboratory account for the fewer observed spectral lines.