Thermal energy from random velocity calculation

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I have a hydrogen atom with a random velocity of;

18.0 x 10^3 m/s

it's thermal energy therefore is;

h=planck's constant

v=frequency of light

E = h x v / 18.0 x 10^3

E = (4.135 x 10^-15)(3 x 10^8 m/s) / 18.0 x 10^3

E= 6.89^-11 Jules/sec

Hoping I've got this right, I've been scratching my head over it for a little while.

Edited by johnrt
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I'm not sure what you are trying to do. "v' is the Greek letter nu (often used to denote frequency), not the Latin letter v (often used to denote velocity). You haven't given a frequency. Also, thermal energy only makes sense for a collection of atoms, not for a single atom. It does make sense to talk about the average thermal energy of members of a collection.

Can you give a little more information about what you're trying to do? Are you trying to find the kinetic energy of the atom?

Edited by George Jones
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I'm not sure what you are trying to do. "v' is the Greek letter nu (often used to denote frequency), not the Latin letter v (often used to denote velocity). You haven't given a frequency. Also, thermal energy only makes sense for a collection of atoms, not for a single atom. It does make sense to talk about the average thermal energy of members of a collection.

Can you give a little more information about what you're trying to do? Are you trying to find the kinetic energy of the atom?

George,

The question I am trying to answer gives the information that hydrogen atoms in the photosphere of a star have random velocities of 18.0 x10^3 m/s. No other values are given.

The question is - calculate the typical thermal energy of a hydrogen atom and estimate the temperature of the photosphere.

Edited by johnrt
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I guess that you want the kinetic energy, and t hen the equipartition theorem can be used to approximate the temperature, but you might not have heard of the equipartition theorem.

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I guess that you want the kinetic energy, and t hen the equipartition theorem can be used to approximate the temperature, but you might not have heard of the equipartition theorem.

Nope I haven't, it's not covered in any of the course notes that I have, so I doubt that can be the way by which the question is intended to be answered. Share on other sites

Do your notes say anywhere that the average thermal energy per atom is 3*k*T/2, where k is Boltzmann's constant and T is temperature?

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The question's looking for you to apply 1/2mv^2 = 3/2 kT

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Hmmm.

My notes only mention the Steffan Boltzmann law in relation to calculating luminosity;

L = 4πR^2 σ T^4

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Hmmm.

My notes only mention the Steffan Boltzmann law in relation to calculating luminosity;

L = 4πR^2 σ T^4

This is the power (energy per unit time) radiated by a spherical (ideal) blackbody, and I'm afraid it doesn't help for this problem.

There is nothing about k*T in the thermal energy section of your notes (or text)?

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Ahh, Ok.

I have found the section of notes that relates to the Boltzmann constant and thermal energy.

However this is in a much later section of notes that my questions aren't meant to cover. So now I really am confused.

I think an email to my tutor is called for.

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Ahh, Ok.

I have found the section of notes that relates to the Boltzmann constant and thermal energy.

However this is in a much later section of notes that my questions aren't meant to cover. So now I really am confused.

I think an email to my tutor is called for.

Yes, I think so. Good luck!

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• 3 months later...

Have you found the answer to this question? It's relatively simple. I can help if you want..

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Have you found the answer to this question? It's relatively simple. I can help if you want..

Indeed I have!

E = 1/2 mv^2

E = 0.5 x 1.6735x10^-27 (mass of hydrogen atom) x 18x10^3 (velocity)

E = 2.7x10^-19 Jules

Thanks for the offer though!

Edited by johnrt

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