Heat is energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objects and systems, but its origin and properties can be understood in terms of their microscopic ...
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1answer
267 views
ratio between work and heat [closed]
I am really stuck on a problem in my textbook:
Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. ...
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1answer
486 views
Will adding cold water to a hot iron pan harm it? Why/why not?
Adding cold water to a aluminum pan can be harmful.
Is this same with iron pan too?
How can it be explained?
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2answers
377 views
Why can't I evaporate water without wind, just heat? (not boiling,evaporating!) Or can I?
So here is the thing, I searched all over the internet for this but all the sources say that I need wind because the process of evaporation goes as follow:
Water particles at the top layer with ...
3
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1answer
218 views
What is the difference between infrared heat and “regular” heat?
In Feynman's terms temperature is the speed at which atoms are 'jiggling'. Now, let's suppose I've just eaten a sizable dinner, and my body temperature just got a tad up. Am I emitting more photons in ...
3
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1answer
584 views
Where does the lost energy go in a rubber band powering a rotating shaft?
Okay, I'm no physics whiz, and this has me stumped. You know those toy airplanes you can get with the rubber-band driven propellers? You twist the propeller a bunch of times, and this stores ...
3
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5answers
329 views
What is the meaning of following expresion $C=\frac{\delta Q}{dT}$ mathematicly
Our professor raised the following question during our lecture in Statistical Physics (even so it's related to Thermodynamics):
Many text books (even wikipedia) writes wrong expressions (from ...
3
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2answers
251 views
Why does it take until the middle of summer before lakes have warm water, but desert sand heats up in hours?
My sister asked me this question and I keep thinking that water would conduct heat much faster than sand. Hence the energy transfer of heat across the lake does not allow it to heat up soon. Sand on ...
2
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3answers
141 views
Heat Equation Equalities
While studying the heat equation, I ran into a few equalities that I cannot understand.
For example, Fourier's law of heat conduction claims that
$$\varphi(x,t)=-K_0\frac{\partial u}{\partial x},$$
...
4
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1answer
72 views
Where does the heat flow in the Earth's crust switch from primarily solar to geothermal?
Ok, maybe more of a geology question than physics, but maybe somebody has been involved in modeling these heat flows?
Essentially I'm asking if we know what sort of depth the heat source becomes ...
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2answers
244 views
Is carbon dioxide a greenhouse gas? [duplicate]
Possible Duplicate:
What experiments prove the greenhouse effect?
I am seeking for a proof that CO2 is a greenhouse gas. I posted this on Skeptic.SE recently but found no help in seeking ...
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1answer
105 views
Why does the aligning of magnetic dipoles in a material cause its heat capacity to decrease?
This is with regards to adiabatic magnetisation.
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1answer
205 views
Physics of the electric hot plate
For an electronics experiment, I began wondering about the electric hot-plates (specifically the temperature dependence over time). If I were to measure the given temperature over time, I assume that ...
3
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1answer
502 views
Calculating time to heat cold water in bowl of hot water
How would I calculate the time it takes to heat a given volume of water to a given temperature with a given temperature T1 when it is submerged in a volume of water with a temperature T2
Estimation ...
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3answers
301 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 ...
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2answers
649 views
design of the heat exchanger…in chimney
I want to design a heat exchanger in a chimney in order to utilize heat from chimney. I have done several experiments, but I could not determine the exact length of tube (carrying water), such that ...
2
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2answers
333 views
Why water will stay on a piece of toilet paper?
I think everyone has tried to blow air (breath) on toilet papers. The papers will get wet. I believe the holes diameters on a toilet paper should be much larger than diameters of water molecules. (The ...
2
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1answer
65 views
Is Joule heating only between charged particles?
The Wikipedia page for Joule heating explains
"It is now known that Joule heating is caused by interactions between the moving particles that form the current (usually, but not always, electrons) and ...
2
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0answers
102 views
Problems in the modern semiconductor/electronics technology?
From what I have read, the problem with modern semiconductors/electronics seems to be quantum tunnelling and heat. The root of these problems is the size of the devices. The electrons are leaking out, ...
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3answers
94 views
How can a strong water current be cold
This is a layman question.
If heat is the motion of atoms, how can a fast moving water current be cold?
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0answers
65 views
How is pool boiling dealt with by today's process design methods?
Designing evaporators and industrial reboilers often requires at initial stages of dimensioning (i.e. when the support from a finite element software tool to model the system of interest, isn't yet ...
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1answer
558 views
Why does burning magnesium explode when sprinkled with water?
Magnesium powder burns extremely well and reaches temperatures of 2500°C. However, attempts to extinguish such a magnesium fire with conventional water (e.g. from a garden hose) only make it worse: ...
2
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1answer
120 views
Why is the crust of my meat pie only slightly warm?
I just cooked a meat pie in the oven. Almost immediately after pulling it out of the oven, I felt that the crust was only slightly warm, but when I cut it open the filling felt very warm. I can't ...
1
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1answer
107 views
Temperature and latent heat
Building a bronze stature we make a mold and pour in the liquid bronze when the bronze hardens we remove the mold.
The mold is made of 3 Kg of steel and the statue has a mas of 1 Kg. The specific ...
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2answers
1k views
Why I will feel colder when I get out from a swimming pool?
A friend of mine told me that because water heat capacity is higher. He also mentioned that it was similar to alcohol on skin effect.
Assume that there are 3 situations.
1. I did not get wet
2. I got ...
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1answer
116 views
Determine the flow and amplitude equation for thermal energy (with Del operator)
It is a question vector calculus and Maxwell's laws. I put it this way. Let's say, we are working in a $3$-Dimensional space ( e.g $x\cdot y\cdot z = 4\cdot3\cdot2$, a certain room/class of that size ...
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1answer
58 views
What is the average total heat incident on Earth's surface each hour?
Just what the title states
Some part or the other of this Globe faces approximately towards the Sun during each 24 hour period. What is the total amount of heat (in calories) incident on average ...
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2answers
183 views
Density of states via a Laplace transform
Is this formula correct?
$$ \frac{-1}{\pi}Im\int_{0}^{\infty}\!dt~\exp(Et)\Theta (t)\exp(i \epsilon t) ~=~ \sum _{n}\delta (E-E_{n}), $$
$$ \Theta (t)~=~ \sum_{n}\exp(-tE_{n}) ,$$
and I have used ...
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1answer
519 views
How to calculate specific heat capacity of an alloy
I have done an experiment in which I measured the specific heat capacity of a coin. I would like to compare the results to the actual value. I have found out that the coin is made of Cupronickel alloy ...
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2answers
169 views
Second Law of Thermodynamics, heat and quantum-level explanation
I heard somewhere that the second law of thermodynamics is stating that some heat (energy) becomes unusable for work (at the scale of the whole universe). Why is it like that? Can't heat be converted ...
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1answer
399 views
Do materials cool down in the vacuum of space?
Do materials cool down in the vacuum of space?
If yes, how does it really work?
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0answers
570 views
What is the insulative value of water?
I am having a hard to finding what the R value of water is. I am trying to compare it to styrofoam (which has an R-Value of 5).
EDIT
Based on the assumption that water has an insulative property, ...
4
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2answers
213 views
How can one feel cold without touching it?
Let me explain.
My shower is inconsistant in how hot it gets. Whenever I turn on the shower, I always put my hand really close to the water, but not touching it, so I can feel the heat radiate from ...
3
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2answers
318 views
Heuristics for specific heat capacities of solids
A didactic question publish in The Physics Teacher (http://tpt.aapt.org/resource/1/phteah/v41/i1/p8_s1) asks which will melt more ice: 100g of metal at 100C or 100g of wood at 100C. (The particular ...
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2answers
673 views
Specific heat capacity
Which of two objects at the same tempreature can cause more intense burns when you touch it: the one with the greater specific heat capacity or the one with the smaller specific heat capacity and why?
...
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2answers
139 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 ...
4
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2answers
148 views
Why is latent heat required?
Why is latent heat required for a system to change its state? (I.e. liquid water to ice) Why the "extra" energy?
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0answers
44 views
What other factors effect the ability of a propigating field of pressure in a gaseous medium to predict gravitational collapse?
What other factors effect the ability of a propigating field of pressure in a gaseous medium to predict gravitational collapse?
Will the only factor influencing the Speed of Sound in this medium be ...
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1answer
82 views
heat of a laptop when placed on a table, when placed on a pile of books and when placed on a bed [closed]
I heard somewhere that it is dangerous to place a laptop on a bed. The reason given was that placing the laptop on the bed blocks (assume that the laptop does not have sideway fans - it only has air ...
4
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1answer
402 views
Greatest volumetric heat capacity
Is there any substance with bigger volumetric heat capacity than water? According to this table water has the biggest known VHC. But I can't believe that in the 21. century we have no special material ...
2
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2answers
234 views
how does heat energy start to speed up a gas molecule?
If it was possible to place a single gas molecule in a cell and freeze it to near absolute zero.
What would the molecule do as it thawed out?
Would it translate the heat energy into it's electrons ...
4
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1answer
4k views
What exactly is the difference between advection and convection?
After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms.
Sometimes, the term convection seems to ...
1
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1answer
191 views
Efficiency of parallel and sequential heat pumps
Consider two identical heat pumps, for example, split-system air conditioners. There're two ways to make them work - in parallel or sequential. Parallel means that "hot" radiators of the machines are ...
1
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1answer
281 views
How would I calculate the convection coefficient in transient convection?
So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I ...
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2answers
314 views
Transient radiation--heating a slab
Hey guys I really need help on this problem.
A ceramic slab of dimentions 5cm x 10 cm x .25 cm has to be heated to $177\,^{\circ}{\rm C}$. The ceramic slab travels on a conveyor belt traveling at ...
4
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1answer
1k views
Why is glass a good conductor of heat?
AFAIK Glass is insulator, it doesn't have free electron. It's said metal is a good conductor of heat because it has free electron, glass doesn't have free electron, why it is a good conductor of heat?
...
2
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2answers
142 views
How would I go about solving this transient convection problem if the mean fluid temperature is constantly changing?
Let's say I have a ceramic slab on a conveyor belt that is initially at $450\,^{\circ}\mathrm{C}$ and there is air being blown over it at a speed of $35 \frac{m}{s}$ with an ambient temperature of ...
2
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2answers
308 views
Intuition behind the concept of heat
Even if elementary, I'm afraid I am still not comfortable with the concept of heat. I can picture heat as some kind of incompressible fluid that is transferred from a body to another in such a way ...
1
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2answers
516 views
Why did the microwave oven only heat my coffe half as much as expected?
A sticker on my microwave oven states its output effect to be 750W, which is 180 calories per second. This means that heating 250g of water by one degree celsius would take 250/180 = 1.4s.
Now, my ...
18
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6answers
3k views
Is fire plasma?
Is Fire a Plasma?
If not, what is it then?
If yes why, don't we teach kids this basic example?
UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify ...
1
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3answers
364 views
Maximum efficiency for a counter-current heat exchanger (double flux controlled motorized ventilation)
I am not sure if I can explain the question correctly because I don't know the name of this mechanism in English.
This is my explanation attempt: In a house, a tube is expelling the air from the ...
