How to find the temperature of a black body?

AI Thread Summary
To find the temperature of a black body emitting photons at a frequency of 4 GHz, the relevant equations involve Planck's Constant and Wien's Displacement Law. The user initially confused protons with photons and struggled with calculations, particularly in determining the wavelength and temperature. After finding the wavelength of 0.075 meters, they attempted to apply Wien's Law but received incorrect results. The correct approach is to divide the constant by the wavelength to find the temperature. The discussion highlights the importance of accurately representing physical concepts in calculations.
sphys4
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Homework Statement


It emits protons with a frequency of 4 GHz, and has a photon energy of 2.65E-24 J.

I tried to use the formula lambda=c/f=vT, but i am somehow getting a negative answer which doesn't make sense when trying to find temperature in (K).

Any help is greatly appreciated.
 
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You'll need the equation involving Planck's Constant, denoted by h[/color]
 
NascentOxygen said:
You'll need the equation involving Planck's Constant, denoted by h[/color]

E=hc/lambda? So i solve for lambda and plug it into my above equation? Does v=4E+9?
 
sphys4 said:

Homework Statement


It emits protons with a frequency of 4 GHz, and has a photon energy of 2.65E-24 J.

Are you sure you have represented the question correctly? Because a hot body emits photons over a whole spectrum of energies.

And I presume you didn't intend to write "protons"? Otherwise, I'm outta here. :eek:
 
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NascentOxygen said:
Are you sure you have represented the question correctly? Because a hot body emits photons over a whole spectrum of energies.

And I presume you didn't intend to write "protons"? Otherwise, I'm outta here. :eek:

Ahh * photons.

And yes, this is the problem.
Suppose a blackbody emits photons strongly with a frequency near 4 GHz. What is the photon energy? And then i found the value that i stated above (in J), which is correct.

The question then asks for the temperature of the black body and that's where I am lost.
 
The wavelength where the radiation is maximum multiplied by the temperature is constant, lambda * T = b. How do you get the temperature?

ehild
 
sphys4 said:
Okay so i found lamba which i got .075

0.075m seems correct. So at 4GHz we are talking about microwave energy, way below visible light. (I wonder is this venturing beyond the limits of black body radiation equations?)

then divided that by b (the constant) and got 25.88 which is still wrong. :(

To find T you need to divide b by lambda.

Considering that the lowest temperature found in outer space is about 3 Kelvin, then I think you've taken us to another universe. :cool:

At least it's not a negative Kelvin. :rolleyes:

Did you invent this question, or it is out of a book?
 
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  • #10
NascentOxygen said:
0.075m seems correct. So at 4GHz we are talking about microwave energy, way below visible light. (I wonder is this venturing beyond the limits of black body radiation equations?)



To find T you need to divide b by lambda.

Considering that the lowest temperature found in outer space is about 3 Kelvin, then I think you've taken us to another universe. :cool:

At least it's not a negative Kelvin. :rolleyes:

Did you invent this question, or it is out of a book?

It's online homework that i copied and pasted, it's okay though.. thank you for your time and attempting!
 
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