Resistor Definition and 894 Threads

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. solour

    Current Through A Resistor That Is In Parallel With A Capacitor

    Homework Statement [/B] My question is regarding part C of the question. Homework Equations V = IR V(t) = V(1-e^(-t/tau)) The Attempt at a Solution My idea is to use Kirchoff's Voltage Law and find the voltage of the capacitor as a function of time, then since the voltage across capacitor is...
  2. nothing909

    Calculating resistor for IGBT and choosing flyback diode

    Homework Statement On the circuit I've drawn up, how do I calculate a current limiting resistor for the gate of the IGBT? The IGBT being used is a stgp6nc60hd. Also, how would I go about choosing a flyback diode for the motor?
  3. G

    Finding resistance of single resistor

    Homework Statement Two resistors are connected in parallel. The total resistance of the combination is 6.0 ohms. If one of the resistors is 10 ohms, what is the value of the other? Homework Equations 1/RT= 1/R1+1/R2 The Attempt at a Solution I got 15 just by doing trial and error, and I'm...
  4. 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})##...
  5. duhuhu

    Can Resistive Heaters Fail in Vacuum Due to Reasons Other Than Temperature?

    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...
  6. 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...
  7. 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...
  8. nothing909

    Calculating resistor values for transistor

    << Mentor Note -- Two threads merged into one >> As a project I have to design a switching circuit for a switched reluctance motor. I've picked all the components I need and I've tried to design the circuit. Open collector - 74LS06N Optocoupler - TLP 251 IGBT - stgp6nc60hd Does the circuit...
  9. 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...
  10. R

    Keep setting fire to discharge load resistor - Wattage limit

    We kept getting some voltage spikes back into our amplifier. One of the things we put in place is a 10kOhm resistor (discharge load) connected to the output of the amplifier. However, the resistor keeps burning and setting on fire. The amp company offered a way on checking this... I'm really...
  11. K

    How do we know if a resistor is added or subtracted?

    Homework Statement I was reading in my physics book about loop currents. However, some resistors are added to the result (R*I) whereas some resistors are subtracted from the result -(R*I). The book uses the phrase "uphill" and "downhill" to describe this, and, indeed, the so called "uphill"...
  12. D

    Solving Resistor Circuit Homework: DC Motor, Rf, Rr, E, If, Ir, Pth

    Homework Statement A shunt-wound DC motor with the field coils and rotor connected in parallel (see the figure) (Figure 1) operates from a 140 V DC power line. The resistance of the field windings, Rf, is 248 Ω . The resistance of the rotor, Rr, is 4.40 Ω . When the motor is running, the...
  13. EddNeedsHelp

    Engineering Solving for resistor values in voltage divider circuit

    Homework Statement So I was studying an example and the picture given simply asked to setup a voltage divider for the values without solving for resistance. However... I want to know if I'm missing something or if this can even be solved: I attached the problem below. Homework Equations...
  14. Planobilly

    What is the effect on audio of using larger wattage resistor

    Hi, In general 1/2 watt resistors is what I see in tube guitar amps. I built one with 1 watt resistors and can not hear any difference. I assume shot noise will decrease with larger wattage values. Other than heat dissipation, how is a 1 watt resistor different from a 1/2 watt resistor...
  15. J

    What is current across 5 ohm resistor

    Homework Statement Find the current across 5 ohm resistor Homework Equations Superposition theorem. Other voltage sources become short circuit and current sources become open circuit. Ohm's law. I = V / R The Attempt at a Solution Using superposition theorem, we get: When only left side 10...
  16. R

    Calculating Voltage in a 6x6 Resistor Grid

    Homework Statement We have a resistor grid with 6x6 squres. ( figure below) If we know the voltage between ##O## and ##A##, what is the voltage between: ##a) O## and ##B## ##b) C## and ##D## ##c) E## and ##F## Every side has the same resistance. Attempt for solution: Because of the symmetry...
  17. 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...
  18. MeaningfromForm

    Super small electronic variable resistor -- Exists?

    Hi I couldn't find of these exist anywhere. Is there a component that is a variable resistor that adjusts based solely on receiving an up/down signal? And maintains its state on powerdown? I don't want this solution to involve any type of software, just a hardware solution. Looking for...
  19. 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...
  20. moenste

    Resistance of the resistor and voltmeter's readings

    Homework Statement A battery of EMF 12.6 V and internal resistance 0.1 Ω is being charged from a DC source of EMF 24.0 V and internal resistance 1.0 Ω using the circuit shown in the figure below. V1 and V2 are high resistance voltmeters and R is a fixed resistor. (a) What is the polarity of...
  21. Elvis 123456789

    Change in entropy of a resistor

    Homework Statement Consider a thermally insulated resistor with resistance R=20 Ω and mass m=5.0 g. The resistor is made of a material with specific heat capacity c=850 J/(g-K) and carries a current of 2.0 A for a time period of 1.0 s. a) Calculate the increase in the temperature of the...
  22. Cocoleia

    Simplifying a circuit w/ multiple resistors & current source

    Homework Statement I am given this circuit...
  23. 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...
  24. moenste

    Resistance of the resistor and of the diode

    Homework Statement A semiconductor diode and a resistor of constant resistance are connected in some way inside a box having two external terminals, as shown in the diagram below. When potential difference of 1.0 V is applied across the terminals the ammeter reads 25 mA. If the same potential...
  25. B

    Finding current in the 25 ohm resistor

    Homework Statement The problem is to find the current in the 25 ohm resistor (left side) http://imgur.com/a/luKCW [Image inserted by moderator] Homework Equations KCL KVL ohms law (v=IR) The Attempt at a Solution My attempt at the solution was to add both power sources together (-5v(-5v...
  26. Z

    Solve for Equivalent Resistance - Resistor is shorted?

    Homework Statement I'm studying for a test and since this is technically a textbook problem I figured I'd post here to prevent being flagged. I have the circuit redrawn. Homework Equations Series: Req = R1+R2... Parallel: 1/Req= 1/R1 + 1/R2... The Attempt at a Solution I want to understand...
  27. JMatt7

    Entropy: gas heated by resistor

    Homework Statement A current ## I=0.2 A ## flows in a resistor ##R = 50 Ω## immersed in a rigid adiabatic vessel that contains ##n=3## moles of Helium. The initial temperature of the system is ##T_0 = 27 °C##. The resistor has a mass ## m = 10 g## and specific heat ## c = 0.2 (cal/K)/g ##...
  28. 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...
  29. chuvacjoe

    What are the currents at each resistor?

    1. The problem statement, all variables and given/known data Homework Equations I3 + I1= I2The Attempt at a Solution [/B]
  30. E

    Power Resistor Immersed In Water

    Homework Statement For the circuit shown below the 20-ohm resistor is immersed in water surrounded by insulating foam; the equivalent resistance through the circuit is 40 ohms. The current through it is 0.75A. What is the power dissipated through the 20 ohm resistor? Homework Equations $$...
  31. M

    Power Dissipated By Resistor is LRC Circuit

    [Note by mentor: this post does not use the homework template because it was originally posted in a non-homework forum.] --------------------------------------------- Problem: What is the average power dissipated by a 25-Ω resistor in an LRC series ac circuit for which the power factor is...
  32. W

    A resistor with current flowing but no dissipation

    If an amplifier (audio or RF) has the collector of a transistor for its output electrode and assuming the transistor operates in its active region (not saturated or cut off) the output impedance of the amplifier will be high (several 10s of kilohms). If now a tuned circuit is connected as a load...
  33. Planobilly

    Resistor noise reduction questions

    Hi Guys, I am looking for a high level overview concerning resistor noise and how to reduce it. I have read the following general statements. Carbon comp resistors are rated at 0 db. I read this somewhere. Vishay metal film resistors MIL-R-10506 are rated at -40 db...
  34. J

    Soving for resistor values and source current-image included

    Question is in image included So, I need to find R2, R3, and Is. I was able to get the correct answer for R3 by doing R3= V/I (R3= 12/1 = 12) . however when I apply that equation to R2 ; R2= V/I. (R2=12/4 =3), I do not get the correct answer. The answer is supposed to equal 4 ohms. Am I using...
  35. Salvador

    Temperature dependant resistor for MAF

    Hi folks, so here's my recent problem, My car has a broken MAF (mass airflow sensor) the semiconductor innards are ok but the very thin metal strip that comes into the airflow tube has become brittle from old age and broken up. I know the MAF works when it sends a low voltage through the...
  36. A

    Calculating Resistance in a Parallel Circuit without Voltage Information

    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...
  37. S

    Discharging a capacitor through resistor and uncharged cap

    Homework Statement Given v0 c1c2 r1 need to find the current on r1 picture switch 1 is closed for long time and on t=0 opened and switch 2 is closed Homework EquationsThe Attempt at a Solution in the attached file i was trying to use kvl assuming that q0(charge on cap before opening switch...
  38. Neil Hayes

    Finding the value of a neutral earthing resistor

    Homework Statement An 11 kV motor is fed by cables from a transformer via switchgear, having a phase impedance of 0.3 + j0.3 ohm. The Earth return path to the transformer neutral has a resistance of 0.42 ohm. Determine a suitable value of neutral resistance if the voltage rise at the motor in...
  39. T

    How Do You Choose the Right Pull-Down Resistor Value for an IC Input Pin?

    Hi, I have this IC Datasheet: http://www.ti.com/lit/ds/schs015c/schs015c.pdf I need a pull down resistor at one of the input pins but I am not sure what value to use. How can I calculate what value resistor I need ?, can someone give me a specific range ?
  40. M

    Graphing the energy in an capacitor, coil and resistor

    I need to graph the current energy on a resistor, capacitor and inductor they are all separate it is not a RLC circuit. This is what I know u(t) = sqrt(2)*220*sin(314*t+π/3) R = 10 Ω L = 3 mH C= 3 mF I have already calculated the current for each component, now I need to calculate the energy...
  41. 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 EquationsThe Attempt at a Solution I have got four equations so far. One is simply using KCL, I1 = I2 + I3 + I4. The other...
  42. Naakicibi

    Resistor parallel to short circuit when finding R_thev ....?

    (sorry, I couldn't figure out how to insert an image from my drive) I have a problem where in finding the thevenin resistance I take out my independent sources and as a result I'm left with a resistor parallel to a short circuit. Should I ignore this resistor when calculating equivalent...
  43. ReidMerrill

    How Do You Calculate Current and Power in a 3-Resistor Circuit?

    Homework Statement Find the current through and power dissipated by each resistor Homework Equations V=I/R ΣIin=∑Iout The Attempt at a Solution Did I set up the loop laws correctly and where do I go from here?
  44. terryds

    What Voltage Makes the 6 Ohm Resistor Absorb 1.5 J/s?

    Homework Statement A circuit is arranged like above. To make the energy absorbed by the 6 ohm resistor every second is 1.5 J, voltage X should be ... Volt Homework Equations V = IRThe Attempt at a Solution [/B] I really have no idea. I just know that it's kinda like wheatstone bridge and...
  45. Silverado

    Power Dissipated in a Sliding Resistor

    Homework Statement The circuit [http://tinypic.com/r/2cwl7bt/9] shows a battery connected across a uniform resistor R0. A sliding contact can move across the resistor from x = 0 at the left to x = 10 cm at the right. Find an expression for the power dissipated in the resistor R as a function...
  46. V

    Find voltage across resistor using mesh current analysis

    I'd like to find Vth by mesh current analysis. Mesh A and B share a current source, so they're treated as one supermesh. What's the equation for this supermesh? Also, do I ignore the loop with the open circuit? Since there's no current flowing there... 2A = ib - ia Anyway, is this the right...
  47. P

    Potential Difference Across Diode & Resistor

    Homework Statement Assume an ideal diode with ##V_t=0.6##v, find the potential differences across the diode V_ab and across the resistor V_bc as the forward bias voltage is varied from 0 to 10v. Hint: equivalent circuits may be useful Embedding the image wasn't working so...
  48. Sollicitans

    Do resistor polarity assignments affect current flow in Kirchoff's second law?

    I guess there's a simple rule, but I can't find it anywhere and it seems I was supposed to know this. I'll appreciate it if someone explains me how it works and also if (and how) is related to the way you consider positive and negative voltages when you apply Kirchoff's second law as shown in...
  49. PhysicsBoyMan

    Find resistance of resistor connected in series

    Homework Statement Two 1.80 V batteries—with their positive terminals in the same direction—are inserted in series into the barrel of a flashlight. One battery has an internal resistance of R1 = 0.280Ω, the other an internal resistance of R2 = 0.155Ω. When the switch is closed, a current of...
  50. 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...
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