# What is Heat: Definition and 1000 Discussions

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. ### How does the rise in temperature of fuse wire depend upon its radius?

I tried the following: We know, Q = mc (delta t) but by Joule's law of heating, we also know that H = I^2 R t Assuming that no heat is lost in the surroundings, we get Q = H => mc (delta t) = I^2 R t => (delta t) = (I^2 R t)/(mc) But m = V d = AL d and R = (rho L) / A => (delta t) =...
2. ### I How does BTU convert to heat in degrees in a greenhouse?

Information online claims sun is 200 btu per sq ft in winter only when sun is perpendicular to plastic or glass of a green house. When sun hits glass or plastic at an angle there are losses. The steeper the angle the more losses will be. Is it possible to calculate how warm a green house will...
3. ### Question about the thermodynamic temperature scale

My first problem is to find the absored and rejected heat. Can I say that it is equal to the work done in an isothermal proccess (##dQ=Pdv##)? My reasoning : We have ##dQ=C_V d\theta + Pdv##. For constant temperature it becomes :$$dQ=Pdv$$
4. ### I Work done in cycle of a refrigerator (in Heat and Thermodynamics by Zemansky)

I guess the first one is wrong. Because in this cycle we have ##|Q_H| > |Q_L|## then ## |Q_L| - |Q_H| ## is negative and caanot be equal with ##|W|##. Am I right?
5. ### I Measurement of heat as an interval measurement or a ratio measurement

Hello! I am new to this forum and I'm not even sure if this is the right place to ask but here goes: I am studying Research Methods. I got to the part where the teacher is teaching us about levels of measurement. They said that there are a few levels but the two that are significant to my...
6. ### B How much heat energy can give out put by ionization gas?

I mean by accelerating electrons and ions for energy levels in atom
7. ### Why does this question make this simplifying assumption?

The question says to "neglect the change of volume of the water". This confuses me. Why do we neglect the change of the water's volume? Let's say we didn't. A = Q/It, where A is area, Q is heat, I is intensity, t is time. Q = mc(deltatheta), mass is constant, specific heat is constant (as mass...
8. ### I Measurement and Thermal Effects Similar?

A weak (one photon at a time) beam of laser light strikes a double slit. In case 1 the barrier forming the double slit is a mirror. In case 2 the barrier is flat black. An array of detectors surround the experiment and can detect the photon whether it goes through the slit or is reflected. In...
9. ### I Is low entropy found in something very hot?

If we have a kg of something that is 100miljon Celsius degrees, and can controlably use this heat somehow, we can sustain life, grow crops, drive steam engines and with these we could build a whole city like New York, we can create a lot of mass with very low entropy, things that are very...
10. ### I Why is ##dQ = dH## still valid for chemical reaction (Callen)?

Consider a system which is characterized by the extensive variables ##(U,V,N_1,...,N_m)##. For a quasistatic process which occurs in contact with some pressure reservoir and where the ##N_i## are constant, one has $$dU = TdS -PdV \implies TdS = dQ,$$ where the implication follows from the First...
11. ### Correct statement about thermodynamics process

I know process B absorbs heat but I can't determine the heat of process A. In adiabatic process, Q = 0 but process A is not adiabatic. I only know both W and ΔU will be negative for process A but how to know Q? Thanks
12. ### I Does heating weaken the strong nuclear/electromagnetic forces

In this steel forging video, does the heat weaken the strong nuclear and electromagnetic forces allowing compression?

34. ### I 1D Heat Transfer Analytical Wall

Hello everyone, I'm trying to solve the transient heat transfer problem within the ID wall. The material is steel, and it is isotropic. The properties are given below : L = 5 mm qin = 0 Tinf = 100 deg C Tini = 20 deg C rho = 7850 kg/m3 cp = 460 W/Kg.K k = 45.8 W/m.K h = 20 W/m^2.K alpha = k /...
35. ### Calculating heat released from excess enthalpy

Hello, I am currently trying to determine the method to calculate the heat absorbed / released when a gas and liquid mix. I believe that this is known as the heat/enthalpy of mixing (or excess molar enthalpy). I also believe, that if this value is negative it means an exothermic reaction (heat...
36. ### Heating up of tyres on the road

I have searched online for this and found that it's due to friction. But for a rolling tyre there is only static friction acting and static friction produces no heat. For heat to be produced the two surfaces in contact must slide over each other i.e. there needs to be kinetic friction. Perhaps...
37. ### B Heat exchange after thermal equilibrium

In screenshot below, systems A and B are separated by an adiabatic wall initially while each of them exchanges energy with system C via a diathermic wall. Once A and B reach thermal equilibrium with C, then A,B are allowed energy exchange via a diathermic wall, and energy exchange between A and...
38. ### I Cannot understand formula for molar heat capacities of an ideal gas

Homework Statement:: I am trying to understand a formula given in our book for determining molar heat capacity of an ideal gas under different thermodynamic processes using a single formula, but it is confusing. The exact formula for different processes is in the screenshots below. Can someone...
39. ### Heat loss from the temperature difference

Hello, My house has some heat loss. As an example I know the outside door temperature. How can I calculate the heat loss delta if I reduce the door temperature by 1 degree? I know that there is a formula to calculate a heat loss based on the U-value of a fabric. But I can't get those values...
40. ### I Heat transfer via air cooling -- which airflow direction is best?

I'm using a stainless steel pan and a fan to cool my coffee down as quickly as possible. Usually, I have the fan blowing down towards the coffee, but this morning I flipped it over to suck the heat out of the coffee and I'm wondering which of the two is the most efficient, especially as, in the...
41. ### Specific Heat Capacity of a metal bar placed into water

Previously solved thermal energy gained by water as Eth= 0.15(4180)(17.6) = 11035.2 J Not sure if its relevant
42. ### The Mystery of Heat Loss: Examining Ice Melting Without Heat Loss

During the procedure, 30% of heat is lost. So that means that 70% of water+container is contributing to melting the ice, right? And the other 30% contributing melting the ice is down to, well, the "heat being lost to the surroundings" (not sure what this really means). We compute the sum and...
43. ### I try to solve a thermodynamics problem on heat transfer

I have some doubts about a thermodynamics exercise I did-I'll write down the text and show how I tried to solve it to see if I reasoned it out right. In a container of thermal capacity ##C## containing ##1.0 kg## of ice at a temperature of ##-4.0 °C##, a mass of ##3.0 kg## of water is poured...
44. ### Heat Radiation question (skin's reaction to UV versus IR radiation)

I am not sure of the answer. But I am guessing that infra-red rays carry more heat radiation than ultra-violet rays, and the heat is instantly felt on our skin when exposed to both these rays. So what we feel is the heat sensation from infra-red rays and that sensation is missing when it's...
45. ### Fourier's Law of Heat Transfer: Conceptual Explanation

Hello, I'm looking over some old school notes and re-learning some basic heat transfer. I have known Fourier's Law (1D: ##q = k\frac{dT}{dx}##) for a long time, but when I look at it now I find it strange that heat flux is inversely proportional to the length of the conductor. I would think...
46. ### How could the discrepancy be reduced between the two readings?

I am able to solve part (a) using the relationship ##\frac {P_1} {T_1} = \frac {P_2} {T_1}##, where ##T_1 = 273.16## since its the triple point of water and ##T_2 =T_s## ##(T_s = ## melting point of sulphur). I use the two readings for thermometer A to get ##P_1## and ##P_2## as mentioned in the...
47. ### pV diagram, ranking heat transfer between 4 processes

Apologies, made a mistake when posting. Please see below post.
48. ### I Temperature change due to mixing liquids, heating and heat losses

Hello, I am stuck how to proceed with the equations below. The problem: A tank containing ##m_0## mass, with a temperature of ##T_0##, is to be filled with a total mass of ##m_1##, with the constant mass flow rate ##G## and temperature ##T_1## during ##t_p## seconds. ##T_0>T_1##. Other than the...
49. ### Work greater than heat given to colder reservoir -- impossible?

photo below... Is it possible to make a machine that would take more heat from the hot reservoir to do work than what would hot reservoir give to the cold reservoir(heat)? Apparently, it's impossible because it violates 1st law of thermodynamics. the thickness of the arrows symbolizes the...
50. ### Python Animating 2D Heat Map with Varying Time Intervals

Consider the following heat map: from scipy import special import numpy as np import matplotlib.pyplot as plt u0=200 r0x=25 r0y=25 rmax=2.5 alpha=2 t=0.575 y, x = np.meshgrid(np.linspace(0, 50, 100), np.linspace(0, 50, 100)) r=np.sqrt((x-r0x)**2+(y-r0y)**2)...