Universe: Stars And Galaxies
Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 19, Problem 47Q
To determine

(a)

The average speed of a Hydrogen atom in the Sun’s atmosphere.

Expert Solution
Check Mark

Answer to Problem 47Q

11.9kms-1.

Explanation of Solution

Given:

Temperature of atmosphere of present day Sun is T=5800K

Mass of hydrogen atom is M=1.67×1027kg

Boltzmann constant =1.38×10-23kgm2s-2K-1

Formula used:

Average speed of an atom is given by the formula,

v2¯=vrms=3KTM

Where

v2¯=vrms is root mean square value of speed, M is the mass, K is the Boltzmann’s constant and T is the temperature.

Calculation:

Substitute the values

vrms= 3×1 .38×10 -23 kg m 2 s -2 K -1 ×5800K 1 .67×10 -27 kg=11,991.01ms-1=11.9kms-1

Conclusion:

The average speed of a Hydrogen atom in the Sun’s atmosphere where temperature is 5800K is 11.9kms-1.

To determine

(b)

The average speed of a Hydrogen atom in the 1M red giant’s atmosphere.

Expert Solution
Check Mark

Answer to Problem 47Q

9.3kms-1.

Explanation of Solution

Given:

Temperature of atmosphere of 1M,T= 3500K

Mass of hydrogen atom is M=1.67×1027kg

Boltzmann constant =1.38×10-23kgm2s-2K-1

Formula used:

Average speed of an atom is given by the formula,

v2¯=vrms=3KTM

Where

v2¯=vrms is root mean square value of speed, M is the mass, K is the Boltzmann’s constant and T is the temperature.

Calculation:

vrms= 3×1 .38×10 -23 kg m 2 s -2 K -1 ×3500K 1 .67×10 -27 kg=9,314.85ms-1=9.3kms-1

Conclusion:

The average speed of a Hydrogen atom in the 1M red giant’s atmosphere where temperature is 3500K is 9.3kms-1.

To determine

(c)

Comparison of the two average values of a Hydrogen atom in the atmospheres of present-day Sun and the 1M red giant.

Expert Solution
Check Mark

Explanation of Solution

Given:

Escape speed from a red giant = 61.9kms-1

Escape speed from the present-day sun = 619kms-1

According to the calculations, the escape speed of an atom in the atmosphere of a red giant is much lower than the escape speed from the atmosphere of the present-day Sun. However, there is not much difference in the average speeds in the respective atmospheres as they are 9.3kms-1 in the red giant’s atmosphere and 11.9kms-1 at the present-day Sun’s atmosphere. Even though more mass could have escaped to the outer space from a red giant than from a main-sequence star, Hydrogen atoms in both these atmospheres are not having the required speed in order to leave the gravitational field. Hence, both of these stars can retain their respective amounts of Hydrogen atoms.

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