Resistor Definition and 65 Discussions

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads for generators.
Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds and forms. Resistors are also implemented within integrated circuits.
The electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. The nominal value of the resistance falls within the manufacturing tolerance, indicated on the component.

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  1. bluesteels

    Power formula for circuit when another resistor is added in

    On Chegg they solve for V using P=V^2/R using 36W and R1= 25Ω, which is equal to 30V then they add R1+R2 = 40Ω and they plug in P=V^2/R and solve for P which is 22.5W I'm confused on why they didn't use P=I^2*R cause you know the system is in series so I is the same and solve for I then...
  2. S

    DC circuit finding Req

    The answer sheet assumes that the resistors in both circuits are in series and that we need to use the equation Req = R1+R2+R3.. to find the Req in both cases. How come the resistors are in series, when there are multiple resistors in a single row? Also, why does the following work yield the...
  3. J

    Circuit problem -- Find the equivalent resistance of this series/parallel resistor circuit

    Having more difficulty understanding the concept, thus I am not showing values. What is causing me confusion is the line in the middle. The first aR and bR are obviously in parallel, but the second aR and bR confuse me. I tried calculating the equivalent resistance from the first aR and bR and...
  4. B

    Equivalent resistor of a simple circuit

    Hi. Anyone knows how to calculate the Req of this circuit? n tends to infinite.
  5. Prabs3257

    Heat dissipated in a Resistor-Capacitor circuit

    I tried to conserve the charge on the left plates of both the capacitors as intially the total charge on both is 48 and at t=t0 the total charge is 36(on c1) +4V(V is the potential across c2) so i got V=3 and then i conserved the energy Initial energy on both capacitor = final energy on both +...
  6. C

    I RC charging - intuition behind equal dissipated energies?

    Assume that a resistor R charges a capacitor C, whose other terminal is connected to the ground. The charge at time t = 0 is assumed to be null and the supply voltage is equal to V. We have, as is well known, ##i = \frac{V}{R} e^{-\frac{t}{RC}}##. Integrating ##\frac{i^2}{R}## between t = 0 and...
  7. M

    Photodiode - circuit questions

    I am a bit confused on a few things regarding photodiodes. Here is are two circuits that I am referring to: or For the second circuit the capacitor is not of importance. Here are my fundamental questions: 1. Why do we need an external voltage? 2. Why do we need a resistor? 3. What is...
  8. P

    Finding the current and voltage for each resistor

    Homework Statement Moderators note: link removed. All images should be uploaded to PhysicsForums. Homework Equations V=IR Series in parallel Series in current The Attempt at a Solution I managed to get the current and voltage of R1 and R2. I've been trying to get the next one R3, but...
  9. Eduardo Leon

    Energy dissipated in the resistors in a 2 mesh RC circuit

    Homework Statement Hi mates, I have problems solving the third part of this exercise, I've already done all the previous calculations. Given the following circuit, where the switch S is open, the power supply = 50 volts and: The initial charge in the C capacitor: QC = 0 coulombs The initial...
  10. marino

    Power generated by a coil rotating in magnetic field

    The problem: a coil of radius r, length l and N turns, rotating with constant angular velocity ω around an axis perpendicular to its simmetric axis and passing for the center of the coil. The coils is submersed in a static magnetic field, intensity B0, perpendicular to the axis of rotation of...
  11. Lapse

    Engineering Finals Study Time! A Two Source Circuit w/Inductor, Cap, and Resistor

    Homework Statement Homework Equations Z = √(XC2 + XL2) XL = 2πƒL XC = 1 / 2πƒC I = V/Z The Attempt at a Solution First off, thank you for all of the help this semester. I'm sure you'll be seeing questions from me in the spring also. Here is how I'm thinking about this problem: 1. Using the...
  12. B

    Unknown Electrolysis(?) reaction occurring

    I have obtained an experimental setup of a Marx bank which has electrolytic liquid resistors. In the tubing of the resistors are various strength solutions of copper sulfate. I was told that the electrodes are copper but there appears to be some sort of plating or other reaction occurring...
  13. A

    Is the source in parallel or series with the resistor?

    Thank you for your time and effort. It is much appreciated. 1. Homework Statement I have attached the problem with the solution to this thread. Basically, the problem asks to construct the circuit model for a generic device by using the data of terminal current and voltage measurements. From...
  14. H

    Find the transient current in this circuit

    Homework Statement Homework Equations The Attempt at a Solution I often do circuit. But still there is always stuff i don't get.. I was asked to find 1) I1 I2 I3 immidiately after S closed 2) I1 I2 I3 after sufficient of time 3) I1 I2 I3 immidiately after S opened Just give me clue...
  15. C

    Find maximum dissipated power

    Homework Statement A constant voltage source V with internal resistance r is connected to a load resistor R. The dissipated power by the resistor R is P=RV^2/(R+r)^2. Show that the maximum power dissipated by the resistor R is achieved when R = r. The maximum of P with respect to R is achieved...
  16. H

    Find the Voltage in the parallel resistor-capacitor circuit

    Homework Statement C1 = 4 micro F C2 = 8 mF R1 = 4 ohm R2 = 8 ohm V = 12 Questions : 1) Find current I when S not closed 2) find Vb, when Vc is 0 3) find Vd, when Vc is 0 4) total charge move from B to D Homework Equations Vf - Vi = F.d/q (not sure this below is useful equations) I = E/Z E...
  17. B

    Energy dissipated in a resistor

    Homework Statement A resistor of resistance 10Kohms has voltage across it described by the function V(t) = 6sin(10t+pi/4)*exp(-2t) Volts Calculate the energy dissipated in the resistor between t=0 and t=0.5 Homework Equations The Attempt at a Solution I have done the definite integral and...
  18. H

    Can you help me find the current through the 15 Ohm resistor branch?

    Homework Statement Homework Equations I = VR Series = current the same, voltage different Parallel = current different, voltage the same The Attempt at a Solution Is the 1 ohm and 15 ohm parallel? I'm still learning to differentiate it. If yes, then R = 15/16 ohm Is the R series to 5ohm? If...
  19. G

    How do you find the current going through a weird circuit?

    Homework Statement Homework Equations at point C: i2 - i3 - i4 i2 = i3 + i4[/B] The Attempt at a Solution I labeled all the currents going through each resistor in the picture[/B] for loop ABC: 2000i1 = 3000i2 + 4000i3 for loop BDC: 3000i5 = 2000i4 + 4000i3 at point C: i2 - i3 - i4 i2...
  20. M

    Finding the time for charging Voltage

    Homework Statement 1. The characteristic decay constant for a capacitor C discharging through a resistor R is the product of R times C. If the initial voltage at time t = 0 is Vo = 13Volts and what is the voltage at time t = 2RC? 2. A capacitor C = 9microFarads is charged from 0Volts to...
  21. L

    What is the current in these 3 circuits right after the switches are opened?

    Homework Statement What is the current through the resistor marked 'R' in all three circuits just after the switch is reopened after being closed for a long time? The Attempt at a Solution The explanation that we were given for (1) is that I = V/2R and (2) I = V/3R and (3) I = V/(R/2) but I...
  22. S

    Resistors in Series - Lab data confusion

    Homework Statement (see my attached photo to better understand where I am coming from!) So after some research, I've discovered that the current at different points in a simple series circuit is supposed to be the same value, and that the voltage is supposed to be different values. I...
  23. S

    Resistors in Series - Lab data confusion

    Hi guys! (see my attached photo to better understand where I am coming from!) So after some research, I've discovered that the current at different points in a simple series circuit is supposed to be the same value, and that the voltage is supposed to be different values. I performed a lab on...
  24. L

    Resistor maze

    Homework Statement Res-monster maze. In Fig. 27-21, all the resistors have a resistance of 4.0 and all the (ideal) batteries have an emf of 4.0 V. What is the current through resistor R? (If you can find the proper loop through this maze, you can answer the question with a few seconds of mental...
  25. prakhargupta3301

    Will there be a difference between the readings of V1 and V2

    I= Current flowing V1= Voltmeter 1 V2= Voltmeter 2 My question is that if there would be any difference between the readings of V1 and V2? We know that: By Ohm's law: V= I.R also: Combined resistance of R1 and R2 will be: 1/RCombined Resistance of R1 and R2= 1/R1+1/R2 The reading in V2...
  26. B

    HOW TO: Stop efficient LEDs from lighting up when off

    Saw an old thread, "Led Lights Burn With Power Off" and it was closed... so let me check out an issue with you all: in this same situation and I don't want the lights softly glowing, could I put a 100 ohm 1/4 watt resister in line to block the teeny tiny induced current? Would it behave well...
  27. Additya

    B Can a wire be called a resistor?

    Can a wire be called a resistor? Also do all circuits require a resistor? If no then give an example of a circuit which doesn't have a resistor. Please thanks
  28. S

    Value of resistor for full scale deflection with 10A

    Homework Statement In order to provide full scale deflection the coil current required in a galvanometer is 190μA and the resistance of the coil in the galvanometer is 35Ω - What is the value of the resistor to be connected in parallel with the meter so that full scale deflection is obtained...
  29. franktherabbit

    Delta-Y transformation of resistors

    Homework Statement Starting from the expression of the Delta-Y resistor transformation work out the conductance transformation equation. Homework Equations 3. The Attempt at a Solution [/B] I will just be using one equation as others are done analogically. My Δ has ##(R_{12},R_{23},R_{13})##...
  30. duhuhu

    Electronics Issues in Vacuum

    I am working on a project for a cube-sat to go up on a balloon to 40 km. My team has been talking to some other groups who have worked on other cube-sats who say that our resistive heaters need to be Kapton heaters rather than 1D heaters like what we have designed for. They claim that our...
  31. solour

    Reducing all circuit resistors to only parallel and series?

    Homework Statement The problem from the textbook is: Is it possible to connect resistors together in a way that cannot be reduced to some combination of series and parallel combinations? Homework Equations V = IR kirchhoff's current law kirchhoff's loop law The Attempt at a Solution I am...
  32. RoboNerd

    Resistor made from two materials

    Hi everyone, I am having problems figuring out how to solve a particular problem. Because I was not able to access PhysicsForums recently, I typed everything about my issues into a pdf file that I have attached below. I am grateful for your help in advance, and make it a great day...
  33. doktorwho

    Engineering Help understanding the solution to a circuit problem

    Homework Statement When the switch is open, the voltage is ##U_{ab}##. When the switch is closed the calculated max current is ##I_{max}##. Calculate the resistance of ##R_p## when its power is max and the current of ##I_g## ##R1=100,R3=200,R4=400##,##0<Rp<100## and...
  34. O

    Find the voltage across the resistor

    Homework Statement A battery with = 12.0 V and internal resistance r = 1.0 Ω is connected to two 6.9 kΩ resistors in series. An ammeter of internal resistance 0.50 Ω measures the current, and at the same time a voltmeter with internal resistance 10.0 kΩ measures the voltage across one of the...
  35. MagicPandaLol

    Why is voltage constant in a wire?

    Hey! I have a question and a drew up a diagram to help out. I drew up a circuit that includes just a voltage source and a resistor. I know the voltage is constant in each of the circled portions of the circuit. As in, as you move through the wiring, the voltage doesn't change from one point to...
  36. Cocoleia

    Simplifying a circuit w/ multiple resistors & current source

    Homework Statement I am given this circuit...
  37. moenste

    Find initial current and resistance in a circuit

    Homework Statement A battery of internal resistance 0.50 Ω is connected (as shown below) through a switch S to a resistor X, which is initially at 0 °C. When S is closed, the voltmeter reading falls immediated from 12.0 V to 10.0 V. The reading then rises gradually to a steady value of 10.5 V...
  38. A

    Finding a Missing Resistor

    Homework Statement Three resistors are connected as shown in the diagram. If the current from the power supply is 250 mA and the current through R3 is 54 mA, what is the resistance of R3? Homework Equations 1/Req= 1/R1 + 1/R2 +1/R3 V=IR The Attempt at a Solution First I used the parallel...
  39. D

    Finding unknown values in DC resistor network via matrices

    Homework Statement I need to get 7 equations to make a 7x7 matrix in order to solve it. I have 4 of them, but I'm not sure how to get the voltages equations. Homework Equations The Attempt at a Solution I have got four equations so far. One is simply using KCL, I1 = I2 + I3 + I4. The other...
  40. P

    How Many coulombs pass through each resistor in a circuit?

    Homework Statement My question relating to physics and electric circuits, is "If a circuit consists of a 12 volt battery and two ohm resistors connected in series, then how many Coulombs pass through each resistor in a second". Thank you all so very much. Homework Equations V=IR The Attempt...
  41. A

    Find the resistance of a resistor using Ohm's Law?

    Hi, I have been at this problem for days and I can't seem to see what I am doing wrong. Here is the circuit layout along with my work As you can see I am running into problem getting values of current that do not add up equal to zero. My professor has never discussed how adding a wire like...
  42. kostoglotov

    Why isn't this largest voltage source given as negative?

    This isn't actually a homework problem, but it is an example in a my textbook that I have a question about... imgur link: http://i.imgur.com/2OglMH4.png Ok, I wanted to clarify some things. I understand that current flowing from a positive terminal to a negative terminal represents a...
  43. kostoglotov

    Power dissipated by resistor -- Right answer, but need insight

    imgur: http://i.imgur.com/9VILpYL.jpg Now, I can easily solve this by applying the formula P_R = \frac{(\Delta V_R)^2}{R} and get all the correct answers. However, the answers feel strange to me intuitively. In the formula above, lowering the resistance increases the power that is dissipated...
  44. G

    Potential difference of each resistor

    Homework Statement What is the potential difference across each resistor? I know that I'll have to incorporate the V=iR equation but I don't know where to start though... My first attempt was with these: R1=4 R2=8 R3=5 R4=6 R5=3 24-I1R1-I1R2-I3R3+I4R4+I5R5=0 but this lead me nowhere so I...
  45. F

    Complex Resistors Problem

    Hey there! I'm having some real trouble deciphering this complex resistor problem. I have heard of the Kirchhoff voltage and current rules and do know how to use them to solve some problems but I'm not sure how to apply them in this context, or if they are even used to solve this. As seen the...
  46. Guidestone

    Strange questions about electrical circuits

    What's up people? I'm new in this wonderful forum. I have several questions about circuits, and they are not really common, I mean, I find them somehow complicated, but I would really come to enlightenment if you guys gave me some clues. 1.- So, let's suppose we got the simplest circuit, a...
  47. P

    Find power dissipated in circuit with a ground

    Homework Statement 1. Find the power dissipated by 12 ohm resistor 2. What is the potential at points a,b,c,d? Homework Equations P=I^2R I=V/R The Attempt at a Solution For a) 3v-IR-6v-IR=0 9v=I(18) I=0.5 P=0.5^2 * 12 = 3 watts But not sure if the ground changes anything b) unsure if ground...
  48. T

    Electrical circuit Source transformation Question

    I'm extreeeeamly rusty at basic circuit theory. I want to transform a sort of infinite arrangement of this circuit: The values themselves aren't important, just the representation of what's happening, all the verticle resistors are the same value as each other, and all the horizontal resistors...
  49. R

    Alternating Currents

    Homework Statement A 10 ohms resistor, a 12 microFarad capacitor and a 28 mH inductor are connected in series with a 170 V generator. A.) At what frequency is the rms current maximum? B.) What is the maximum value of the rms current? Homework Equations A.) Fo = 1 / 2pi sqrtLC b.) Irms = Vrms...
  50. MushroomLT

    Can a different Ohm rating resistor burn a pc motherboard?

    Hello, my motherboard recently has stopped working, so I returned it to warrany, they fixed it, but after a few months the board broke again, but unfortunatly the warranty has ran out, so I'm attempting to fix it myself in the freetime :D So I have found a resistor on the motherboard, that looks...
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