What is Power dissipation: Definition and 70 Discussions

In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to a final form, where the capacity of the final form to do mechanical work is less than that of the initial form. For example, heat transfer is dissipative because it is a transfer of internal energy from a hotter body to a colder one. Following the second law of thermodynamics, the entropy varies with temperature (reduces the capacity of the combination of the two bodies to do mechanical work), but never decreases in an isolated system.
These processes produce entropy at a certain rate. The entropy production rate times ambient temperature gives the dissipated power. Important examples of irreversible processes are: heat flow through a thermal resistance, fluid flow through a flow resistance, diffusion (mixing), chemical reactions, and electrical current flow through an electrical resistance (Joule heating).

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  1. patric44

    Power dissipated in this circuit with 2 batteries and 3 resistors

    Hi guys I am struggling to find the power dissipated in the total circuit , my answer didn't match the solution in the book the circuit is simple i used Kirchhoffs rules to find the following : loop 1 : $$10-10I_{1}-40I_{3} = 0$$ loop 2: $$20-20I_{2}-40I_{3} = 0$$ and $$ I_{1}+I_{2}=I_{3}$$...
  2. A

    Active power dissipated by a resistor from DC to RF

    Hello all PF members! I was wondering about the power dissipated by resistor at high frequency which is: ##P=Re\left \{ U\cdot I^{*} \right \}=Re\left \{ \frac{\left |V^{+} \right |^{^{2}}}{2\left |Z_{c} \right |}\cdot (1-\left |\Gamma \right |^{2} )\right \}##, (1) where: ##Z_{c}## -...
  3. B

    Power dissipation question I^2 R

    I understand that when using the equation I^2 * R that current is meant to be constant in each component? I got the idea from this video So how can we use this equation to find the relationship between varying current against power? As the current is at a constant?...
  4. Benjamin Sorensen

    Calculating the Power Dissipation of a Wire

    I'm having trouble verifying an experiment I ran to determine the power dissipation of a heating element. 13.15W of power was applied to 3ft nichrome wire. Temperature readings were collected until they stabilized at 128.5F (room temp was 70F). I want to create a mathematical model of the system...
  5. A

    Average power dissipation for induced current

    Homework Statement A wire shaped as a semi-circle of radius a rotates about the axis OO’ with a constant angular velocity ω in a uniform magnetic field with induction B (attached figure). The plane of the rectangular loop is perpendicular to the magnetic field direction. The total resistance of...
  6. Metals

    How to find power dissipation of a resistor in this circuit?

    Here is an image with information: https://i.snag.gy/UMCRig.jpg I have calculated the total power dissipation as 11W. What I don't see is why R1 has a higher dissipation rate than R2/R3, and my main question is how do I calculate the power dissipation of R1? I get that R2/R3 are in series so...
  7. E

    Alter resistance for max power dissipation?

    1. The problem Given a circuit with a 30V source and five resistors. The circuit can be drawn as two boxes. Resistor 1 (R1 = 300ohm) is in series with the source. R2 (300ohm) in the middle of the two boxes, and the remaining resistors (550 ohm) in series at the other side of the box. The...
  8. toforfiltum

    Mean power dissipated in resistor in ac circuit

    Homework Statement Homework EquationsThe Attempt at a Solution I am surprised that this question came up, I haven't learned ac circuits yet. I don't know how to solve this. I just added both values and current and divide it by two, which gives me 1.5A, since I thought it's the average but I'm...
  9. A

    Power dissipation in capacitor circuit

    Capacitor connected to a battery of certain internal resistance. If it is asked to calculate what is power dissipated as heat, Does -the voltage across capacitor X current through capacitor- gives heat dissipated or should we add heat dissipated in battery by considering its internal resistance.
  10. B. Vane

    RCL Circuit: 2 Resistors, 1 Capacitor, 2 Inductors

    Homework Statement NOTE: Image uploaded with thread shows problem in clearest possible form. V = (45v)sin(80[pi] t) Resistors 1 and 2 = 50 Ohms Inductor 1 = 20 mH Inductor 2 = 2.5 mH Capacitor = 50 uF a) Find the power dissipated by each resistor. b) At what frequency will both resistors...
  11. eee_engin33r

    System Loss In Terms of I why not V?

    We all know that the system loss in transmission line is i^2R. So, in order to reduce the loss we diminish the current flow through the line by means of transformer. My question is i can also calculate system loss by the formula v^2/R where v is the potential across transmission line. So...
  12. baby_1

    Wave Power Dissipation: Solving Pozar's Book Problem

    Hello Here is a problem of Pozar's Book(mircowave). and here is solution: my problem is I don't know how he obtain -40.6 because |T|^2 (T is Reflection Coefficient ) is return power and 1-|T|^2 is transfer powe but 10log none of them return -40.6 , what does -40.6 and how can calculate it?
  13. A

    Calculating Fan Size: Not Driven by Motor

    Hey, I'm trying to find a fan that will dissipate 1471.5W. The fan is going to be driven via a belt connected to a driving spool and not driven by an electric motor. How do i go about calculating the required fan size? Is there anywhere i can look at fan specifications for fans that are not...
  14. Q

    The average power consumed -- where is my mistake

    Homework Statement We have the circuit in the figure.I have to find the average power consumed by all the elements and the source. Homework Equations P=0.5*(I^2)*R P=-VmImcosθ/2 The Attempt at a Solution The inductor consumes zero inductive power. I apply nodal analysis at node Vo We have...
  15. F

    Power Dissipation along power lines and Resistance value

    Hello Forum, It is well known that the electrical power dissipated (in the form of heat) by a resistor of resistance R connected to a battery of voltage V is: P_diss = (V^2)/ R or equivalently P= (I^2)*(R) Clearly the smaller the resistance R, the more the dissipated power because R is at...
  16. A

    Mesh analysis and power dissipation

    Hi I'm taking an intro course to electrical and computer engineering and I'm having trouble figuring out part c of number one. I have attached a copy of my solutions to parts a and b which I believe are right (correct me if I'm wrong please) however when I calculate the power dissipation of each...
  17. C

    Power dissipation limit for a resistor

    I am confused about the concept of a power dissipation limit for a resistor. Basically for a resistor the product of the current through it and the potential across it should not exceed 0.25 watt otherwise it starts to heat up and act in a non-linear fashion. Is this value just a constant or is...
  18. S

    Engineering Help with circuits (Current, Voltage Drop, and Power Dissipation)

    Homework Statement Basically, I need to know the power dissipation (W) for three resistors using aw 12V battery: 120, 80, and 50 ohms. https://webwork2.uncc.edu/webwork2_files/tmp/Fall2014-Engr1201-Common/img/2ff2f0ce-cb10-3786-8109-c42346130316___1a2e5eeb-8657-3983-941f-b7d8a9123afa.gif...
  19. D

    Power dissipation in this circuit

    Hey Guys, Can you see what is wrong with this circuit? It looks fine to me but I am being told that it is incorrect and will not work. I am pretty sure I am wrong and am willing to ask for help in understanding why this wouldn't work. Please see attached picture for further info and any...
  20. D

    Power dissipation at high ambient temperatures

    Hello, This is my first post on this forum and I better warn you that there maybe some poor grammer and spelling mistakes. Given what I had to aggree to in order to register I'd like appologies in advance to all those people who are offended by such things. I'm looking at a problem with...
  21. Y

    How does atmospheric dissipation affect UV light measurements?

    I am looking around for some sort of equation regarding optical power dissipation of light (ultraviolet light in particular) in the atmosphere but i cannot find anything. I know that UV light obeys Rayleigh scattering but I don't know much else. I'm trying to figure out for example, if I shined...
  22. D

    Understanding Power Dissipation in Resistors and Ohm's Law

    Homework Statement i let r = 1 ohm, so i get effective r = 1.5 ohm, , since P=VI, i get my I = 8A, so i get the power dissipation of RESISTOR P = 8W , so the 4W remaining for both Q AND R , why power of R is 2W? i hope someone can explain this. Homework Equations The Attempt at a...
  23. U

    Oscillating charge, larmor power dissipation

    Homework Statement A z-polarized incident EM waves hits a small charge (-q) bounded to a massive charge (+q) with spring constant k0 and frequency ω. (a) Write down the equation of motion (b)Find time averaged total power dissipated. (c) Find classical scattering cross section σ...
  24. A

    Internal resistance of the battery and power dissipation

    I got this question ( i won't include a lot of details because this is not the homework forum) where i need to calculate the power dissipation due to internal resistance. What i did is , i calculated total V and total R and I , then i treated the battery as a normal resistance ( eg. a 1kohm...
  25. L

    Metal chassis resistor power dissipation

    I need some information on power dissipation of metal chassis resistors. I have 47 ohm, 50W resistors. (digikey part #A102169-ND) I hooked them up to 24V. So current flowing is about 0.51A But the resistors get too damn hot to touch(48-55 deg C, just after a few mins(~5mins). The power...
  26. P

    When can we use Vpp in calculations involving Ohm's law?

    Homework Statement So today in lecture, my professor talked about VRMS. I understand VRMS and its relationship to DC power dissipation, however, in lab today I became very confused. In lecture, we were told to use the VRMS value when applying Ohms laws/power equations (P=VI). Then, later, in...
  27. M

    Difference power dissipation and actual power dissipation

    difference "power dissipation" and "actual power dissipation" Hi, Is it possible to explain me the difference between "power dissipation" and "actual power dissipation" for a resistor ? I really can't understand the difference...
  28. L

    Calculating CFM based on Power Dissipation and Max Junction Temp

    I know how to select a heat sink based on Power dissipation and max junction temp. But how do I relate this to CFM of a fan. How I calculate CFM based on pd and max junction temp?
  29. E

    Conductive disc power dissipation in oscillating field

    Homework Statement A disc of conductivity σ is in an axial magnetic field B = B0cosωt The disc has radius a and thickness s Homework Equations possibly dP/dv = JE (dot product of two vectors) but I have absolutely no clue if it is relevant or not. I think J=σE might be relevant, but I...
  30. R

    Power dissipation in a circuit (Kirchoff's Laws)

    Homework Statement Three resistors, R1 = 27 Ω, R2 = 42 Ω, and R3 = 53 Ω, are connected in a multiloop circuit, as shown in the figure. Determine the amount of power dissipated in the three resistors. Homework Equations Junction Rule Loop Rule The Attempt at a Solution I...
  31. N

    Relationship between power dissipation in wires and temperature

    Hello, I am wondering if anyone knows any correlations or equations that can give me the temperature of a wire due to power losses. I understand how to calculate the power loss in the wire, based on wire resistance and current (P=I^2*R) but how do I turn this into a heat transfer problem and...
  32. P

    Current, Power dissipation in a cord

    Homework Statement An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 1.2m (4ft ) is connected to an electric heater which draws 15.0A on a 120 V line. How much power is dissipated in the cord? Homework Equations P = IV R = ρL / A P = V^2/R...
  33. BruceW

    Power dissipation in parallel circuit

    Right, so I was going over some old (basic) electromagnetism principles (to make sure it doesn't all fall out of my head). And I was thinking about two resistors in parallel, assuming some constant dc voltage across them. And I was thinking about the power dissipated by this simple circuit. And...
  34. O

    Relation of resistance to power dissipation

    Equation (p=i^2 * R) seems to suggest that the rate of increase of thermal energy in a resistor is reduced if the resistance is made less. "Eq" : p =v^2/R seems to suggest just the apposite . How do you reconcile this apparent paradox?
  35. C

    Power dissipation in resistors

    Calculate the power dissipated in R1, R2 and R [/b] Previously i worked out the Current I1, I2 and I3 so i planned to use this to calculate the power dissipated; For current i got; I1= 0.8409 A I2= -0.4545 A I3= 0.39 A I used I^2/R to get the following answers R1 =...
  36. T

    Help with resistor power dissipation homework

    This question is in reference to the diagram here: http://imageshack.us/f/17/ecediagram.jpg/ Find the average power dissipated on the resistor. Assume Vth for the diodes is 1V, N1 = 1000, N2 = 100, the transformer is ideal (non-lossy), and V(t) is a purely sinusoidal voltage with frequency...
  37. G

    Maximum Power transfer theorem ( Power dissipation in resistors in circuits)

    the equation P = (E2R) / [(R-r)2 + 4Rr] We say that when R=r , P = E2/4R which is said to be maximum.. But if I say R→∞ , then r→0 and then P = E2/R which is greater.. So, shouldn't power be maximum for max R ?
  38. R

    Electrical Circuit - Power dissipation

    During a Lab we had a simple purely resistive circuit hooked up to a 10 VDC power supply with an adjustable voltage output. In order to determine the power dissipated by the circuit we were asked to determine the source voltage while the circuit was DISCONNECTED... we were not told why... In the...
  39. K

    How to Find Power Dissipation of different ICs

    I've been looking over how to find power dissipation for voltage regulators, op-amps, comparators, logic gates, and amongst other things. Ive looked at some resources and I'm not getting what each variable means. From what I understood so far I've seen PDstatic = Vcc*Icc where Vcc and Icc...
  40. R

    This is about power dissipation.

    i got part (a) by using the equation Vab + E - Ir Which gives 26.57V (also the current = 1.171A) Having trouble getting the power dissipated, any ideas?
  41. K

    Power dissipation due to temperature change

    Homework Statement Heater dissipates 500W when applied potential diference is 110V and wire is 800C. How much power would it dissipate if the wire temperature were held at 200C? Homework Equations a=4.0e-4 p=V^2/R Rf=R0(1+a(T-T0) where R is resistance after temp change...
  42. J

    Maximum power dissipation for resistors

    there are 3 resistors of, different values. 470o,22o and 100o. but each one is 500W I want to connect them in series/parallel in order to dissipate the maximum power 500W. I have connected 4,22o in series and 2, 100o in series, 1, 470 in parallel. but the dissipation is not maximum. the...
  43. S

    Power Dissipation in Resistive Circuit Conceptual Question

    Hey guys, so I have a homework question that I have already solved one way, but when I try it another way I can't seem to get the correct answer. First of all, the question is: "A single resistor is wired to a battery as shown in the diagram...
  44. R

    What is the Maximum Power Dissipation for a Zener Diode Regulator?

    Homework Statement The following is a diagram of dc power supply with a Zener diode regulator. For what load current is the power dissipation of the Zener diode maximum? How would you find the approximate value of this maximum power dissipation...
  45. H

    Power Dissipation by R at t=3.7ms:

    Homework Statement The current through a resistor is i(t) = 2sin(30t + 169°), and R = 50Ω What is the power dissipated by R at t = 3.7ms? Homework Equations p = i2R or p = .5(Vmax)(Imax)*(cos(\phi-\theta)+cos(2*\omega*t+\phi+\theta)) The Attempt at a Solution I feel stupid...
  46. J

    Calculating Power Dissipation in a Circuit

    If I ran over a problem asking for power supplied by a non-ideal battery, or a battery with an internal resistance. Do I account for the internal resistance when I calculate the power dissipation? Or do I just account for the loads (finding the total resistance excluding the internal...
  47. B

    How to find power dissipation in combination circuit?

    Homework Statement What is the power dissipated in the 34-Ohm resistor? Homework Equations P=RI^2 The Attempt at a Solution I have found the total current in the system as well as the current through the resistor, and keep getting 1.88, which is incorrect. Any suggestions on...
  48. A

    Power dissipation in RC circuit

    When a capacitor is charged by a battery half the power is dissipated as heat and half is stored as potential energy within the field of the capacitor. Similarly a resistor dissipates all power that the battery supplies. Now here's my question: In an RC circuit where is the power dissipated...
  49. B

    Estimate Power of CMOS Inverter Circuit - 0.12um Tech

    I want to estimate the power of a CMOS inverter circuit. I want to ask that is there any software for simulation purpose to give the power of CMOS inverter. The second problem I have is that when you calculate the dynamic power of CMOS dynamic power = Vdd2*CL*f This dynamic power depends...
  50. R

    Power Dissipation (more than one battery)

    Homework Statement For the circuit shown, find the power dissipated by the 10.0 ohm resistor. (as attached) Homework Equations P=IV=I2R=V2R V=IR The Attempt at a Solution I really don't know where to start with this. I'm basically tied up in the fact that there are three...