Tagged Questions
0
votes
0answers
92 views
Calculating the Heat Losses of Convection and Radiation [closed]
A water pipe for central heating with length $L=10m$ and diameter $25 mm$ is running over a cold attic with $T_{air} = 278 K$. The radiation temperature of the surroundings is usually lower than the ...
0
votes
2answers
85 views
Can there be energy with no force or energy with no power?
I think that both force (number of newtons) and power (p=ui(?)) implies that there is energy so we can't have force without energy and we can't have power without energy(?)
But can there be energy ...
2
votes
2answers
114 views
Would a laser with four possible energy levels be better than three?
I'm wondering about achieving population inversion for a laser. I learned that without an active medium, it's not possible to create a laser with only two energy levels, but it would be possible with ...
1
vote
1answer
102 views
Specific electron energy gap values $E_{i+1}-E_i$ vs. photons with arbitrary energy $\hbar \omega$
The energy levels of electrons in an atom are quantized $E_i$. A photon of a specific momentum $\vec p$ and energy $$\omega=(E_{i+1}-E_i)/\hbar$$ hits an atom and gets absorbed. Okay now say the ...
0
votes
3answers
274 views
How can there be heat in a vacuum?
I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc.
If heat is caused by thermal energy being radiated from particles ...
2
votes
1answer
111 views
Does magnetic geometry determine the scaling of a Polywell fusor?
Does magnetic geometry determine the scaling of a Polywell fusor?
Forgive imprecise terminology here - by "magnetic geometry" I mean the configuration of the magnets, the configuration that creates ...
1
vote
1answer
420 views
Wein's fifth power Law and Stephan Boltzmann's fourth power laws of emissive power
Wien's fifth power law says that emissive
power is proportional to
temperature to the fifth power.
But the Stefan–Boltzmann
law says emissive power is
proportional to temperature to the fourth power.
...
4
votes
3answers
364 views
Cosmic ray hazards
The Pierre Auger Observatory site mentions the detection of a 3E20 eV (48 J) cosmic ray whose energy, well above the GZK cutoff, was based on an analysis of its atmospheric shower. This was equivalent ...
