# What is Joule: Definition and 81 Discussions

The joule ( jowl, jool; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

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1. ### What is the relationship between entropy and pressure in thermodynamics?

Hi, Starting from dS in term of H and P, I'm trying to find ##(\frac{\partial H}{\partial P})_t## in term of ##P,V,T, \beta, \kappa, c_p##. Here what I did so far. ##ds = (\frac{\partial S}{\partial H})_p dH + (\frac{\partial S}{ \partial P})_H dP## ##ds = (\frac{\partial S}{\partial H})_p [...
2. ### What is the Definition of the Joule and How Does it Relate to Energy?

Mentor's note: Moved from HW for a better fit Homework Statement:: A joule is defined as "the energy transferred to an object when a force of one Newton acts on that object in the direction of its motion through a distance of one meter." Explain this definition. Relevant Equations:: 1J = 1N.m...
3. ### How Does Joule Thomson Expansion Affect Gas Temperature?

Wikipedia says, Unlike a free expansion , in Joule Thomson expansion work is done causing the change in internal energy. Whether the internal energy increases or decreases is determined by whether work is done on or by the fluid; that is determined by the initial and final states of the...
4. ### Joule heating effect - qualitative explanation

Hi, I understand mathematically why using low resistance results in a greater heating effect. Could someone give an intuitive and microscopic picture of why the current contributes more to a greater power dissipation by the resistor rather than the resistance contribution to the power...
5. ### How to work out Joules needed to perform work

Hello all! First post here, and I apologize in advance if this question belongs elsewhere- I'll learn as I go. I am interested in knowing more about energy and performing work. In particular, if I have an object I would like to lift, how much energy I need to expend to do that. Take for...
6. ### Convert solar radiation from Joule per cm square to Watt per meter^2?

I have solar radiation data in the units of Joule per cm^2 (joule per square centimeter) measured hourly. I want to use this data in evapotranspiratin calculation which requires radiation units as Watt per meter squared. How can I do this conversion?
7. ### Thermodynamics: Joule / Brayton Cycle - Specific Work Done Question

Relevant Equations: Specific Work Done: w = \frac{p_2 v_2 - p_1 v_1}{1-\gamma} (1) w = \frac{R}{1-\gamma} \times (T_2 - T_1) (2) Thermal efficiency: \eta _{th} = 1- \frac{1}{r_p ^ {\frac{\gamma - 1}{\gamma}}} = \frac{w_{out} - w_{in}}{q_{in}} = \frac{q_{out} - q_{in}}{q_{in}} (3) Context...
8. ### Conversion between Watt and Joule

example) E = 2734.2 joules per gram P = 2.73 x 109 watt/gram q: How can this conversion work? E = 21000 joules per gram P = ?
9. ### Joule Heating and the Thomson effect in Drude theory

Homework Statement ##\mathbf A##.Joules heating Consider a metal in a uniform temperature in a static uniform electric field E.An electron experiences a collision, and then after a time t, a second collision. In the drude model , Energy is not conserved for collisions, for the mean speed of an...
10. ### Bypassing a joule thief until voltage gets low enough

I'm working on a small crank-able light using a DC motor,capacitors, and LEDs with a joule thief to drain the capacitors completely when the voltage in them drops too low for the LEDs. However I want the power from the capacitors to be able to go directly to the LEDs before the capacitors drop...
11. ### Calculating how many Joules are required to make a photon

A double covalent bond of nitrogen (N2) is 15.58eV Now let's go into a example. if i have a laser that is 477nm and i do 1240/477nm then i get 2.6eV per photon. Now if i do (15.58eV / 2.6eV) it equals ~6 photons. Now to figure out how many Joules are required for 1 photon I do (6.626*10^-34S *...
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### Pressure increase required for 1 Joule of work

Homework Statement Estimate the pressure increase required to impart one joule of mechanical work in reversibly compressing 1 mol of silver at room temperature. Same process for alumina. Homework Equations W=-PdV dV=V(alpha)dT-V(beta)dP dT=0 The Attempt at a Solution I used the work...
13. ### I Joule-Thomson Effect: Explaining Qualitatively

I'm trying to understand the Joule-Thomson effect in a more qualitative way. Here's my attempt at an explanation: Real gases experience intermolecular forces. If we expand a gas whose attractive interactions dominate, it'll cool down. This is due to the potential energy increasing and the...
14. ### What Causes Maximum Joule Heating in a Resistor Circuit?

Homework Statement 2. Homework Equations [/B] Consider the following circuit where: $$R_A=330 k\Omega$$ $$R_B=220 k\Omega$$ $$C= 2.2 nF$$ $$v_1(t)=6u(t) V$$ $$i_2(t)=-10u(t-t_2) \mu A$$ $$t_2 = 12 ms$$ All the currents go clockwise (with the obvious exception of the current source)...
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### How can I represent these resistances on a diagram?

1. The problem statement, all variables and given/known d Hi have this problem but I don't know how to represent, however I've tried. The problem says: You are designing an electric grill and you have to choose a resistance circuit between the circuits shown the figure. Consider that every...
16. ### B What Effect Does Opening a Valve in a Vacuum Have on Air Molecules?

Hi Suppose there is a 1 m3 cylinder containing 1.3 kg air at 25 C. The cylinder is sitting in a vacuum place. The air inside the cylinder will exert a pressure of almost 1 atm. The cylinder also has a valve which can be opened to let the air out into surrounding vacuum. The average speed of...
17. ### Confused with the relationship between Volts, Current, and Power

Homework Statement For an engineering assessment (first year with no electrical background), we are using a solar panel to power an element for a distillation system. we have calculated our heat energy output requirement that we need from our heating element as being 800 J/s. For simplicity we...
18. ### Joule heating in internal resistances of a solar cell

Hi , How can I calculate the resistive heating occurring in the internal resistances of a solar cell ? Are ohm's law or the power dissipation relation P=RI2 applicable in this case ? if not the case how can we calculate the resistive heating there? Thank you in advance for your help
19. ### The Joule Thompson Coefficient -- Throttling effect

Say I have a line of steam with temperature 800 deg C, at 10bars connected with it is a partially evacuated tank 0.01 bar pressure, room temperature. The connection was built with a long capillary and a valve. Does throttling effect experience when the valve suddenly opened? Why and why not?
20. ### B Physics 101 refresher question -- Confused about the definition of a Joule

we all know the equation for KE 1/2mv^2 you do this simple math and you get an number that is in KE units , Joules. so, why is the KE unit equation, 1 Joule = Kg x (m^2/s^2) ?? 1Kg traveling at 1m/s would have a KE of 1Joule, but using the KE equation, it would be 1/2 a Joule. why is...
21. ### Why are work and energy different even though they have the same units?

Work unit is said to be Joule and Energy unit is also Joule. Work formulas in F x S ( Force x Displacement) . We know 1 J = 1 F x `1 s Now Energy is also measured in Joule(J) So can we state : E = 1 F x 1 s as 1 J = 1 F x 1 s that is E = W Then why work and energy are different by definition...
22. ### Do Joule Thief's Work With Supercapacitors

I have a supercapcitor to power some of my small projects. The only problem is that the voltage drops gradually, unlike a lithium ion battery, in which the voltage is mostly stable throughout. My boost converter that I am using to boost the voltage up to 5 volts, stops working with an input...
23. ### Is a joule also known in nutrition as a kilojoule?

I just came across Table 2 on pg 173 of...
24. ### Does turning a spoon in water raises the temperature?

Homework Statement I read about Joule's experiment proving the transformation of mechanical work into heat. But say I have a bowl with some water, and I start turning a spoon in it very fast, thus doing work - the water won't get hotter! What am I missing? Homework Equations conservation of...
25. ### How much energy can be generated by a swinging pendulum 60 kg

I would like to make a pendulum go on moving by a permanent magnet that pushes the pendulum back with a force that is big enough to make it swing back with the same height. Can anyone tell me how much energy could be generated by a pendulum with height is 2 meter and 60 kg, swinging 90 degrees...
26. ### Can The Joule Coefficient be Derived Using the First Law and Maxwell Relation?

The Joule coefficient, μJ, is defined as μ = (∂T/∂V)U. Show that μJ CV = p – αT/κ Relevant equations Cv=(∂U/∂T)v κT=-1/V*(∂V/∂p)T α=1/V*(∂V/∂T)p dV(T,p)=(∂V/∂T)pdt+(∂V/∂p)TdpWhat I have attempted was to make μ = (∂T/∂V)U=(∂T/∂U)V(∂U/∂V)T=(∂U/∂V)T*Cv-1. Then α/κT=(∂V/∂T)p/(∂V/∂p)T because the...
27. ### Converting Coulombs to Joules Without Voltage

Hi Is it possible to convert coulomb to joule without knowing volt?
28. ### Thermal Radiation: Calc Total Emitted Joules in Certain Temp Range

Dear forum I am working with thermal radiation. This is the specific formula: P = σ ⋅ A ⋅ T4 P = emitted effect (W, J/s) σ = Stefan-Boltzmann constant (5,67 ⋅ 10-8) A = area of object (m2) T = temperature of object (K) How can I get to know the...
29. ### Modeling technique for Joule heating

Good Day, I am looking for mathematical modelling of Joule heating of a simple cantilever beam . Can anybody provide me good source of relevant material. Thanks in advance.
30. ### Joule Thief -- Which transistor should I use?

Hi everyone..I'm trying to build a Joule Thief circuit operating on a 1.5V cell. Which transistor should I use? I have BC547 but I'm not sure it will work...Suggestions are welcome..
31. ### Joule thief : number of turns around the ferrite core

Hi everyone, I have to build a simple Joule thief circuit for school. Here it is :(http://upload.wikimedia.org/wikipedia/commons/8/83/Joule_thief.png). The resistance of the resistor is fixed to 1 kOhms, the voltage across the "dead battery" is about 1.5V, the transistor needs about 0.7V to...
32. ### What really is a Pascal and a Joule?

Hi forum, First time poster. I'm in thermo this year and it's the first time working with pascals and joules. My teacher and most post just jump right into the equations, 1Pa = 1N/m^2 and 1J = 1N * M. But what really is a pascal? I get what a N is, force to move 1kg*m/s^2. If I convert N, I get...
33. ### Converting Calories to Joules: Uncovering the Correct Conversion Formula

Lets suppose we have 2000 kcal and we want to translate it joule. 1 calorie is 4,2 J/gC isn't it so I think it will be 8400000 g m^2/s^2 But my teacher says its 8400000 kg m^2/s^2 Which one is true Thanks
34. ### A problem about Calorie and Joule transformation

Homework Statement There's a person and he ate a hamburger which its 2000 kcal.And he wants to spend this energy . he will be weightlifting and he will lift 45 kg to 2 meters.How many times he can lift it ? Homework Equations W=Fx or W=mgh The Attempt at a Solution 2000...
35. ### Joule Heating of Metals with Different Resistivities

Hello, I am a high school student carrying out a physics experiment. I created a short circuit in order to see how much heat different types of metals would release when a current is running through them (4.5 A). In my experiment, I tested three different types of metals: Brass, Stainless...
36. ### Joule Heating in Carbon Fiber w/ DC Current

Ok so as fare as I understand the equation for Joule heating in a material with a DC current is I^2*R. I am trying to calculate for the heating of carbon fiber in an argon environment. Carbon fiber has a resistivity similar to graphite (roughly 5.0*10^-7) I am trying to calculate for 3.3VDc...
37. ### Joule Coefficient at Constant U

Homework Statement Using basic thermodynamic relations, show that the Joule Coefficient is given by: Homework Equations {\left(\partial T \over \partial V \right)_U}=-{T^2 \over C _v}{\partial \over \partial T} \left(P \over T \right)_V The Attempt at a Solution I started with the cyclic...
38. ### What is the Derivative of P/T with respect to T?

Homework Statement Hi, i have a little problem with a demostration, I hope you can help me. Homework Equations this said that we have a system, a gas is containing in a recipe, there's no heat exchange neither work with the enviroment, only an expansion v to 2v, we have to find that...
39. ### Joule Heating Project: Maximizing Glycerol Vaporization

Hi all, some background info, thanks for reading and helping! I'm working on a project, the portable device is to vaporize glycerol(300 C). In an attempt to maximize vapor production, I've decided to skip the experimentation and calculate the optimal specs for each part. Also pardon my...
40. ### Joule Expansion: Cooling Effects & Kinetic Energy

I read on 27 chapter from Blundell's Thermal Physics 2nd edition. For ideal gases, Joule expansion doesn't cool gases. But for real gases, Joule expansion makes cooling effects. And this book(page 314) says that when gases expand, their potential energy of molecular interactions...
41. ### What is a joule, when you calculate relativistic energy?

Energy is E=γmc^2, but when I calculate this, will my result be in joules? I am unsure what the units are when I calculate it, and I keep hearing people saying joules. Also, what is PJ and MJ?
42. ### How did we come about dicovering energy and why is Joule its unit?

When my textbook talks about energy it starts with kinetic and potential. The derivation goes like this. F=ma=m(dv/dt)=-mg then they split the derivative using chain rule (dv/dt)=(dv/dy)(dy/dt) therefore since (dy/dt)=v we get F=mv(dv/dy)=-mg then they write mv dv= -mg dy...
43. ### Joule heating ansys workbench

Hello, I have the following problem: I would like, from a tungsten filament which an electric current is imposed, find the temperature emitted from the filament (Joule heating) on ansys workbench. I have to study a thermoelectrical , but I can not find any tutorial. Does anyone have...
44. ### AZINGLY, for the Joule cycle there is no heat flow at all, so it is 1-0 = 1.

Diesel, Otto , Joule TRICK? Hi Guys, I try to callculate the efficiency for a cycle Process. For Diesel, Otto and Joule Processes you can write the efficiency as a really small equation. I have seen that for example sometimes the adiabatic equation is used, but i don't understand in which...
45. ### Joule free adiabatic expansion dT=0?

In that experiment , the internal energy is zero , volume increase , pressure of system decrease, then temperature will constant ? Thanks
46. ### Entropy Change from Joule Expansion

Assume we have an ideal gas of N particles inside a thermally isolated cylinder of volume V, and that the cylinder is equipped with a piston that can trap the air on one side. (Assume the piston occupies no volume in the cylinder.) Initially, the piston is fully withdrawn and the gas occupies a...
47. ### Joule Thomson Effect: Adiabatic Free Expansion & Derivation

Is the equation JT = (1/Cp)(2a/RT - b) valid for adiabatic free expansion of real gases only? How was this equation derived?
48. ### The temperature change of an ideal gas, Joule Kelvin expansion (const. enthelpy)

Homework Statement This is the last part of the question. So far have been made to derive: ## \mu _{\text{JK}}=\left(\frac{\partial T}{\partial P}\right)_H=-\frac{1}{C_P}\left(\frac{\partial H}{\partial P}\right)_T ## Then ##\left(\frac{\partial H}{\partial P}\right)_T=V - T...
49. ### What's with this Joule Thief thing?

It's amazing that a name like that can grab the attention of so many people and trigger such a flurry of constructing. Is looks to me as if it's a way of driving a non linear device like an LED is such a way that it produces more light output than it would from a battery. Is it not just...
50. ### Converting Newton to Joule: Understanding Energy Transfer in Crankshafts

I want to know how Newton can be converted to energy (Joule). At least approximately... For example let's say a crankshaft transfer a force, - exactly 100000 Newton How much energy would be transferred be per second, - included all what is "lost" to heat etc..