It's the physical property that indicates the degree/intensity of heat present in a substance or an object. It can be expressed and measured according to various scales.
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2answers
467 views
Why is the temperature outside the airplane lower than the ground temperature?
seems the airplane is nearer to the sun, so the sun should more directly shine on the plane. But when I travel, the airplane temperature is much lower than the ground. Why is the temperature so low?
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1answer
780 views
Using resistance and temperature coefficient formula
What is the correct way to use the resistance and temperature correlation formula from http://hyperphysics.phy-astr.gsu.edu/hbase/electric/restmp.html?
In particular, does R have to be the higher ...
1
vote
0answers
232 views
How to liquefy Hydrogen?
I have got a science project and my teacher has recommended me to do "Liquefying Hydrogen". I have been continuously thinking about that but I have not come to a solution. Can anyone please tell me ...
7
votes
2answers
203 views
Do you pay more for gas when the day is warmer?
Found this at the gas station yesteday - got me thinking...
0
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1answer
86 views
What is a good reference for the mechanical properties of materials at cryogenic temperatures?
I want to research various the properties of various materials, namely tensile strength at cryogenic temperatures (~20K). I was wondering if a freely available database of material properties exists.
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1answer
453 views
How are the CPU power and temperature caculated/estimated?
From Wikipedia
The power consumed by a CPU, is approximately proportional to CPU
frequency, and to the square of the CPU voltage: $$
P = C V^2 f $$ (where C is capacitance, f is ...
2
votes
1answer
78 views
If the temperature of 2 materials are the same does that mean the molecules are vibrating at the same speed?
Pretty much what the title says. My base question is this. Assuming I take a piece of steel, and a piece of PVC plastic and I measure both their temperatures and find they are the same. I then take a ...
1
vote
2answers
138 views
Using CO2 to air condition a room
I'm trying to determine how much dry ice or liquid nitrogen I would need to cool 3300 cubic feet, about 90,000 liters of air, from about 100F (37.78C or 310K) to about 90F (26.67C or 299.81K). I'm ...
3
votes
3answers
331 views
Proof of existence of lowest temperature $0 K$
Im mathematics there is a concept of infinity meaning that whenever you pick a number and say that it is the smallest/Largest there is a way to further reduce/increase that number by ...
4
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1answer
491 views
The speed of sound is proportional to the square root of absolute temperature. What happens at extremely high temperatures?
The speed cannot increase unboundedly of course, so what happens?
2
votes
4answers
1k views
What kinds of materials contract the most in cold temperatures?
I know that water expands in the freezer, but I'm curious about which materials contract in response to cold temperatures --- and most importantly, which ones undergo the most drastic changes?
1
vote
1answer
209 views
Thermodynamics, bullet fired into ice
I'm beginning to study basic thermodynamics and I want to solve this exercise:
It fires a lead bullet from $3g$ to $30^oC$ with a speed of $240\frac{m}{s}$ to a block of ice at $0^0C$. How much ice ...
23
votes
2answers
2k views
Before a once-warm lake starts to freeze, must its temperature be 4°C throughout at some point?
This is a problem I just started puzzling over, and I felt this would be a good forum to check my reasoning. So here are the relevant observations followed by my question:
Water achieves its maximum ...
1
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1answer
139 views
Calculating temperature of water in the freezer
Assuming water volume ($V$), initial water temperature ($T_0$) and environment temperature ($T_e$) are known, what is the easiest way to calculate temperature of water in given time ($T$)?
For the ...
0
votes
1answer
150 views
Mixing Water at Different Temperature
If I have cup of water at room temperature (say, $25^\circ$C). What would be the resultant temperature if I pour another cup of same amount of water at $100^\circ$C to it? Is it simply ...
1
vote
2answers
518 views
How do we determine the temperature of a Black Hole?
How do we determine the temperature of a Black Hole?
Since we cannot see a Black Hole, which I presume, is because it absorbs light, would it not also prevent radiation from escaping, making ...
0
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2answers
349 views
What is the physical or mathematical meaning of the Gibbs-Duhem equation?
The Gibbs-Duhem equation states
$$0~=~SdT-VdP+\sum(N_i d\mu_i),$$
where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?
4
votes
2answers
1k views
How to calculate the evaporative cooling rate needed to protect a house from forest fire
Recently in our area there has been a large forest fire and I've been looking into home defense from such things.
I am not a physicist - but can do some basic math.
I was wondering how I could ...
1
vote
1answer
129 views
what will happen when I continuously heat a closed heavy iron box half-filled with water?
I mean what will be the situation inside? All water vaporized, Equilibrium, Temperature-pressure situation.. boiling point increase/decrease?
Thanks for your time.
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2answers
453 views
Colour emitted at a specific temperature (color temperature?)
There are quite a few nagging questions I have been having over the years, I do not require a full explanation, just some guidance in my assumptions and pointers if I am very wrong.
My basic ...
2
votes
1answer
460 views
Inductor with controlled temperature coefficient
Let's assume we have an air-spaced inductor made of copper wire.
As temperature changes, due to thermal expansion of physical dimensions of the coil, its inductance changes too.
1) Is there a way to ...
2
votes
2answers
949 views
Will the hole on a metal disc expand or contract upon heating? [duplicate]
Possible Duplicate:
Will a hole cut into a metal disk expand or shrink when the disc is heated?
The metal disc of diameter D1 has a hole in it and the diameter of the hole is D2 (D2
Now, ...
3
votes
1answer
200 views
Local Mach number for an airfoil
I would like to know how to calculate the local Mach number on the upper surface of an airfoil given the ambient temperature, the local velocity on the airfoil surface, the freestream velocity, and ...
3
votes
3answers
477 views
What does it take to derive the ideal gas law in themodynamics?
How can the ideal gas law be derived from the following assumptions/observations/postulates, and these only ?
I'm able to measure pressure $P$ and volume $V$ for gases.
I notices that if ...
11
votes
3answers
859 views
Prove that negative absolute temperatures are actually hotter than positive absolute temperatures
Could someone provide me with a mathematical proof of why, a system with an absolute negative Kelvin temperature (such that of a spin system) is hotter than any system with a positive temperature (in ...
1
vote
2answers
137 views
Correlation/relationship between human magnetic field and body temperature [closed]
Is there any relationship between human magnetic field and body temperature?
I am looking for studies on this topic.
3
votes
1answer
123 views
In a Sterling Engine, does heat from the hot side transfer to the cold side?
A Sterling Engine is a closed system. The "hot" side oscillates between higher temperature with higher pressure and lower temperature with lower pressure. Does Nature switch back and forth between ...
0
votes
1answer
519 views
What's the temperature distribution of a plane wall insulated on one side with no internal heat gen.?
Let's say we have a plane wall that is insulated on one side, exposed to a fluid on the other side, and has no internal heat generation. Would the shape of the temperature distribution be a constant? ...
0
votes
1answer
288 views
Increase of threshold current by temperature in a laser diode
I read somewhere that if we increase the temperature of the material in a laser diode the threshold current for lasing also increases. Can someone explain to me why is this happening? What is the ...
2
votes
1answer
270 views
How do I find average temperature given a temperature distribution?
I was told to find the temperature distribution of a wire with a current going through it. So I found $$T(x)=T_{\infty}-\frac{\dot{q}}{km^{2}}[\frac{cosh(mx)}{cosh(mL)}-1]$$
I need to find the ...
2
votes
4answers
597 views
What does third law of thermodynamics tell us?
I just have a question concerning the third law of thermodynamics.
The third law describes that the entropy should be a well defined constant if the system reaches the ground state which depends ...
5
votes
6answers
2k views
How is gradient the maximum rate of change of a function?
Recently I read a book which described about gradient. It says
$${\rm d}T~=~ \nabla T \cdot {\rm d}{\bf r},$$
and suddenly they concluded that $\nabla T$ is the maximum rate of change of $f(T)$ ...
5
votes
4answers
974 views
Should I heat my room when I'm not here, energy-efficiently speaking?
I was wondering as it's getting cold : is it better for my electricity bill to shut down completely my (electric) heater during day, and to turn it on again when I come home (then it will have to heat ...
1
vote
1answer
748 views
change of resistance in semiconductors due to temperature change
I have a question that popped up in an old exam I just can't find a way to solve.
If you drop the temperature of this material from room temperature (I guess around 300K) to 0C (273K) the ...
3
votes
2answers
839 views
Why are refrigerators 4 degrees and freezers -18 degrees?
I assume that the refrigerator's temperature of 4 degrees has something to do with the fact that water is densest at that temperature. Does that inhibit microbe growth? But what about the freezer, ...
3
votes
3answers
220 views
How Is It Possible To Measure Extreme Temperatures? (>2M Deg)
Linked Article: Fusion: X-ray laser zaps solid to 2 million degrees
The quest to create nuclear fusion may have come a step closer when scientists heated solid matter to two million degrees with ...
2
votes
1answer
832 views
Heat Flux and Spatial Temperature Gradients
The derivation for Heat Equation I am reading starts by stating
Net change of heat inside $[x,x+\Delta x]$ = Net flux of heat across boundaries + Total heat generated inside $[x,x+\Delta x]$ and ...
4
votes
1answer
268 views
What are conditions for the existence of a critical value (for a phase transition)?
Can there only be a critical temperature if there is some natural unit for an observable in the model, i.e. if there is a natural scale for something? Otherwise I don't see how for a system there ...
2
votes
1answer
240 views
Steady State Temperature of an Object Orbiting the Earth
This may be irrelevant or stupid to ask but I couldn't come up with a good answer. At least, we could not agree on with my friend the other day.
I would like an estimate of the temperature of a human ...
1
vote
1answer
271 views
Given two boiling temperatures and pressures, how can I find the latent heat?
I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat ...
2
votes
3answers
187 views
How to “read” the temperature of an abstract system?
How can I interpret the parameter temperature $T$, if I'm not given the description of the system in terms of the equation of state, $E(S,V\ )$ or $S(E,V\ )$ and so on.
In many systems it makes sense ...
2
votes
3answers
351 views
Opposite of Cryogenics
Cryogenics is related to very low temperatures, so, what is the term when referring to very high temperatures?
0
votes
0answers
43 views
RH change with temperature change plus water required to return volume to same RH at new temperature [closed]
A building of air volume 30,000 cubic meters at elevation 400 ft MSL has an interior temperature of 50F and relative humidity of 50%. If the air is warmed to 68F, how much water (in liters) should be ...
2
votes
3answers
82 views
Certain material heating water in a recipient
I don't know how to resolve a problem, but I don't want the answer since I'm almost going to have it resolved.
What the problem says is we have 85 liters of water at 7ºC in an iron pot of 29kg. We ...
0
votes
1answer
137 views
Is this a simple system in which no heat transfer is possible?
Let's say that a hot gas is trapped in a metal box. This metal box is magnetically suspended in another structure with a low temperature. The inner box does not touch anything. And there is a void in ...
4
votes
5answers
8k views
Which direction does air flow?
I remember learning this in high school, but have forgotten it, and can't seem to find it anywhere online.
Air travels from areas of high pressure to low pressure...correct? So if I have a cold room ...
4
votes
3answers
644 views
How to understand temperatures of different degrees of freedom?
So I'm reading this book, where after the preface and before the models there is a section called General Notions and Essential Quantities, which introduce some things I don't understand. They regard ...
1
vote
1answer
3k views
Why does a gas get hot when suddenly compressed? What is happening at the molecular level?
My guess is that the molecules of gas all have the same speed as before, but now there are much more collisions per unit area onto the thermometer, thus making the thermometer read a higher ...
1
vote
2answers
650 views
How to calculate the temperature of a receiving point from concentrated solar power?
I'm exploring a DIY project about solar power and found very little resources that can explain in a not too simple but not too advanced way how to go about calculating important values in solar power, ...
0
votes
1answer
159 views
Does a water cooker element have to be 100C to get water to cook?
I understand that a water heater element is basically just adding energy to the mass of water in the container. So does that mean that the heater element only has to keep adding energy while the water ...
