How to find the temperature of a black body?

[sphys4]

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.

 

[NascentOxygen]

You'll need the equation involving Planck's Constant, denoted by h[/color]

 

[sphys4]

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?

 

[NascentOxygen]

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.

 

[sphys4]

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.

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.

 

[ehild]

Use Wien's Displacement Law http://en.wikipedia.org/wiki/Black_body#Wien.27s_displacement_law

ehild

 

[sphys4]

Use Wien's Displacement Law http://en.wikipedia.org/wiki/Black_body#Wien.27s_displacement_law

ehild

Okay so i found lamba which i got .075, then divided that by b (the constant) and got 25.88 which is still wrong. :(

 

[ehild]

The wavelength where the radiation is maximum multiplied by the temperature is constant, lambda * T = b. How do you get the temperature?

ehild

 

[NascentOxygen]

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.

At least it's not a negative Kelvin.

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

 

[sphys4]

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.

At least it's not a negative Kelvin.

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!