In a laboratory experiment on emission from atomic hydrogen in a discharge tube only a small number of lines are observed whereas a large number of lines are pressent in the hydrogen spectrum of a star .This is because in a laboratory

Options

A. the amount of hydrogen taken is smaller than that pressent in the star
B. the temperature of hydrogen is much smaller than that of the star
C. the pressure of hydrogen is much smaller than that of the star
D. the gravitational pull is much smaller than that of the star

Answer

To solve the question regarding the difference in the number of spectral lines observed in a laboratory experiment on atomic hydrogen compared to those present in the hydrogen spectrum of a star, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Spectral Lines**:
- Spectral lines are produced when electrons in an atom transition between different energy levels. Each transition corresponds to a specific wavelength of light emitted or absorbed.

2. **Laboratory Conditions**:
- In a laboratory setting, hydrogen atoms in a discharge tube are typically at lower temperatures. This means that the energy available for excitation of the electrons is limited.

3. **Excitation Energy**:
- The excitation of electrons in hydrogen atoms is directly related to the energy absorbed by the atom. Higher energy (or temperature) allows electrons to jump to higher energy levels, resulting in more possible transitions and thus more spectral lines.

4. **Star Conditions**:
- In contrast, stars have extremely high temperatures, leading to a greater amount of energy being available for excitation. This means that electrons in hydrogen atoms in stars can reach much higher energy levels.

5. **Comparison of Excitation**:
- Since the excitation in stars is significantly greater than in laboratory conditions, the number of possible transitions (and therefore the number of spectral lines) is much higher in the spectrum of a star.

6. **Conclusion**:
- The reason why only a small number of lines are observed in the laboratory while a large number are present in the hydrogen spectrum of a star is due to the difference in temperature and energy available for excitation. The temperature of hydrogen in the laboratory is much lower than that of the star.

### Final Answer:
The correct answer is that the temperature of hydrogen is much smaller than that of the star.

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