Heat Definition and 1000 Threads

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The various mechanisms of energy transfer that define heat are stated in the next section of this article.
Like thermodynamic work, heat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of state, for example its internal energy, or for example its enthalpy. This is to be distinguished from the ordinary language conception of heat as a property of an isolated system.
The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. Such methods are called calorimetry.
The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy (being transferred), the SI unit of heat is the joule (J).

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  1. YoungPhysicist

    I Wavelength approaching the Planck length

    If I heat up an object,the object emits a electromagnetic wave with a shorter and shorter wavelength. But if I heat an object up to Planck temperature, and making the EM wave that it emits has a wavelength of Planck distance,what will happen when I heat it up even more? Will the wavelength...
  2. J

    Calculating Total Energy with Dimensional Analysis | Screenshot Included

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  3. S

    Calculating Heat Capacity in a Bomb Calorimeter using Combustion of Toluene

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  4. Y

    How does solar radiation contribute to heat transfer through windows?

    I am doing an assignment about heat energy transfer and passive cooling. I understand that heat energy is transferred into rooms through windows by conduction, but I'm confused about if heat energy is also transferred through windows by solar radiation and where infrared radiation comes into...
  5. K

    Heat Buildup in Complete Insulation Box

    Supposed you have a box of size 1 square foot and the insulation is 100% efficient.. meaning there is no transfer of any heat outside.. and you put a lamp with glass surface temperature of say 50 Celsius (155 Fahrenheit). Would the air temperature in the box keep increasing... can it reach 1000...
  6. Krushnaraj Pandya

    Thermodynamics problem: Heat capacity of a Gas

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  7. Krushnaraj Pandya

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  8. Krushnaraj Pandya

    How Is Heat Generated from Friction in Physics Problems?

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  9. A

    Excess Heat Generated By a Liquid Ring Pump

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  10. J

    Calculate the final temperature of the solution

    Homework Statement Consider the dissolution of CaCl2. CaCl2(s) Ca2+(aq) + 2 Cl-(aq) ΔH = -81.5 kJ A 10.6-g sample of CaCl2 is dissolved in 109 g of water, with both substances at 25.0°C. Calculate the final temperature of the solution assuming no heat lost to the surroundings and assuming...
  11. M

    Steady Heat Eqn between two cylinders

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  12. Death eater

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  13. SchroedingersLion

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  14. F

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  15. M1gu3l

    Calculate Heat Loss from Pipes: Tips & Example Calculation

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  16. evinda

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  17. Rahulx084

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  18. K

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  19. C

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  20. Comeback City

    Heat Transferred to a Falling Object

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  21. T

    A heat exchanger is to be used to heat a process liquid with....

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  22. Gregs6799

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  23. B

    B Photon Gas in a Box w/ Heat Conductor

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  24. C

    I The amount of time it will take to melt ice

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  25. C

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  26. S

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  27. G

    Laminar flow in a tube, heat transfer coefficient-sanity check

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  28. J

    Simple reversed heat engine problem

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  29. TheSlovakEngineer

    Storing Energy as Heat in Vegetable Oil

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  30. T

    Best way to heat up metal plates?

    Hey there! I want to make a rosin press from scratch. I have a big press with 2 inch thick metal plates, probably about 4 inches wide and 10 inches long. I need to heat these plates up to 230 degrees Fahrenheit and press them against each other with product in between them. I am going to fasten...
  31. fluidistic

    I How come electrons and phonons lead to the heat equation?

    Phonons on their own lead to the common heat equation. One sees that for example in insulators or non doped semiconductors. However in metals (or conductors), the electrons are the ones that are mostly responsible for the heat transfer, which extremely surprisingly to me, is also of the form of...
  32. Y

    Thermodynamics: help regarding the coefficient of heat transfer

    Hi! Basically I have some tasks in thermodynamics calculating the heat transfer through a wall. I have been attempting to solve the following problem: “Calculate the heat transfer through the exterior wall in a building, where the temperature inside the building is 20 °C and the temperature...
  33. shintashi

    Friction of a Wheel on the Axle?

    So say I've got a wheel who's outer radius is 12" and the radius of the axle is 1.5", so the simple machine here is an 8 to 1 ratio. So I am wondering, since 1/2mv^2 is for kinetic energy, and the velocity here is 1/8th, does it mean the friction is 1/8th or 1/64th? does it get 1/8th hotter or...
  34. C

    Temperature change in a metal due to heat from a distant animal?

    In bolometers, incoming radiation warms a strip of material. this material will have a large thermal coefficient of resistance, leading to a (small) resistance change in the material. the inventor, Samuel Pierpoint Langley apparently used this to detect a cow from 1/4 of a mile away using a...
  35. TheExibo

    How can heat change be measured under constant pressure?

    So enthalpy is the heat content of a system at constant pressure. Enthalpy change is equal to the heat absorbed or evolved by the system at constant pressure. If my understanding is correct, a system whose temperature goes up will return back to that starting temperature if pressure is kept...
  36. katelr

    When/How does thermal radiation stop (if it stops) and conduction

    Consider two solid objects in the vacuum (of different materials, if you will) at different temperatures approaching each other until they make "perfect contact" through flat surfaces (no gaps or defects, so that thermal contact conductance effects are absent, even though interfacial thermal...
  37. R

    Heat Loss of Hot Air: Get the Facts on Temperature & Insulation

    Hi everyone I'm new around here and I wonder if anyone can help please. I'm taking hot air off the chimney stack inside a factory at a temperature ranging between 700 and 400 degrees going through a 4 inch stainless steel pipe with 3mm wall thickness. This pipe line will be about 35 meters long...
  38. F

    Problem involving specific heat and graph

    Homework Statement A researcher studies the heat transference between an iron block and an unknown substance, inside an adiabatic calorimeter. In successive experiences he puts inside the calorimeter the unknown substance, always in its solid state and with temperature θs = 20ºC, and the iron...
  39. H

    MATLAB Crank-Nicholson solution of 1D heat equation

    I wish to numerically compute solutions of the 1D heat equation using the Crank-Nicholson scheme: The equation is: \partial_{t}u=\partial^{2}_{x}u I use the discretisation: u_{i+1,j}-u_{i,j}=s(u_{i+1,j+1}-2u_{i+1,j}+u_{i+1,j-1})+s(u_{i+1,j+1}-2u_{i+1,j}+u_{i+1,j-1}) Where s=\delta...
  40. T

    Is the human body a heat engine?

    If this is a valid enough definition of a heat engine: All heat engines transfer heat energy from higher to lower temperatures, and do work in the process. ... then is the human body a heat engine?
  41. A

    How much heat in joules must be added to 0.841 kg of aluminu

    Homework Statement How much heat in joules must be added to 0.841 kg of aluminum to change it from a solid at 130 °C to a liquid at 660 °C (its melting point)? The latent heat of fusion for aluminum is 4.0 x 105 J/kg. Homework Equations Q = mL Total = mc∆t + mL = m(c∆t +l) The Attempt at a...
  42. J

    Heat Flow Rate: Dependence on Conductivity & Temp Diff

    I recently read in a Khan Academy article that the rate of energy exchange through heat across a material of thickness ##d##, surface area ##A##, and thermal conductivity ##k## can be approximated by $$\dot{Q} = \frac{kA\Delta T}{d}$$ where ##\dot{Q}## is the heat rate and ##\Delta T## the...
  43. J

    Does Heat Radiation Decrease the Number of Photons Over Time?

    Homework Statement Homework EquationsThe Attempt at a Solution No . The number of photons should decrease . As the rate of heat transfer decreases with time , the net electromagnetic radiation from the hot body to the surroundings decrease . Heat radiations are composed of photons ...
  44. Ed Lenarduzzi

    Compressed air, heat and pressure?

    Yes compressing air increase its temperature but does that necessarily increase pressure? In an pellet gun a spring driven piston compresses the air which increases the temperature but wouldn't any increasing pressure simply retard the piston's advance? Because the chamber volume is not fixed...
  45. Andres Padilla

    Why this special case occurs in an exchange of heat

    Homework Statement Hello. First of all sorry about this question, it has to do a little with heat transfer from engineering. This situation is not real, I was working in a proyect and this doubt came to me. I have a heat exchanger of parallel tubes. Water flows in a tube and oil flows in...
  46. Beanyboy

    Exploring the Relationship Between Color and Temperature in Thermal Measurements

    There's a passage in Kumar's (excellent) book, "Quantum", which has me confused. He notes that Planck is aware that as the temperature of a heated poker rises, the colours change from red through to bluish white. Later in the passage, he refers to Herschel's earlier work on the relationship...
  47. M

    I What is the solution to the heat equation with a constant added?

    I have seen how to solve the heat equation: $$ \frac{ \partial^2 u(x,t) }{\partial x^2} = k^2 \frac{ \partial u(x,t) }{\partial t} $$ With boundary conditions. I use separation variables to find the result, but i don't know how to solve the equation plus a...
  48. Cassius1n

    Heat loss in a conductor based on Fourier's law

    Homework Statement Find the admissible current density Jadm for a wire that has no insulation and also for a wire that has two layers of insulation and compare it to Jadm for the case when the wire has only one layer of insulation.2. The attempt at a solution and equations In the image I've...
  49. F

    What is the Specific Heat of an Ideal Blackbody?

    Hello, I was thinking about how a blackbody (and any other type of body) eventually reaches a steady-state, constant and finite temperature once the absorbed energy is equal to the emitted energy. The specific heat of a substance indicates the temperature change causes by the...
  50. Krushnaraj Pandya

    Change in temperature when a gas is in a moving container

    Homework Statement Some gas at 300K is enclosed in a container. Now the container is placed on a fast moving train.is the change in temperature of the gas the same as the change dT observed when train suddenly stops? Homework Equations 1/2mv^2=dU?? or dU=0?? The Attempt at a Solution...
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