What is Resistor: Definition and 891 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. funmi

    Voltage between two points on an empty wire and also across a resistor

    In a closed circuit the battery sets up a potential difference which causes charge to flow. I understand potential difference as the measure of electric potential energy per unit charge, the amount of energy required to move a charge from one point to another per charge. for example when a...
  2. D

    Finding the current and voltage for a resistor

    I tried to solve it by loop currents. So on the left mesh the loop current ##I_1## goes clockwise and on the right mesh the loop current ##I_2## goes counterclockwise. I ended up with the following equations: 1) ##V_1-R_1(I_1+I_2)-R_2I_1=0##; 2) ##V_2-R_3I_2-R_1(I_1+I_2)=0##. To find the...
  3. Tryhard314

    Voltage drop across a capacitor and resistor in series

    In this circuit a battery,Capacitor,and a resistance are in series. For simplicity assume that there is a +4V in the positive terminal of the battery and -4V in the negative one and let A be the capacitor plate connected to the positive terminal and B the capacitor plate connected to the...
  4. J

    Electronics Calculating Resistor Size for 3V Battery: A Guide

    Found this online I added 3 volt battery how do you figure out what size resistor to use?
  5. lalallaland

    Two batteries with inner resistor in parallel

    I am kind of stuck at this exercise and I would like some help. Thanks a lot!
  6. R

    Finding Equivalent Resistance, Current, and Voltage across a resistor

  7. Physics lover

    Maximum power in this resistor circuit

    My attempt-: So the resistance is coming to be negative.Can anyone tell me my mistake.Thanks.
  8. P

    Boiling off Liquid Argon Using A High Powered Resistor

    I understand that liquid argon is constantly boiling when it's in contact with the air in the lab, but I want to increase that boil off rate. Because of that, I got myself a high powered resistor (1 ohm, 100 W) and got the highest current power supply I had (5A). When I supply about 5 V and 5 A...
  9. Bheshaj

    Voltage drop: What do we mean when we say that voltage drops across a resistor?

    What do we mean when we say that voltage drops across a resistor?and what does it mean when we say that a point is at lower potential as compared to some other point?Can we say that potential is potential energy per unit charge?
  10. 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}## -...
  11. X

    Determining the optimal resistance of a variable resistor

    Let ##R## denote resistance of standard resistor and ##R_v## the resistance of the variable resistor. I know that ##I = \frac{V}{(R_v + R)}##. Now I also know that ##P = I^2 R_v##represents the power dissipated by the variable resistor and that I need to maximise ##P##. The problem I am having...
  12. Oannes

    Finding the Current Through a Resistor (Working With Parallel and Series)

    Here is the actual question. And here is my attempt at a solution In Summary I did the following Found the Equivalence Resistance to Be 5.9 ohms and the Current throughout the entire resistor to be 1.53 Amperes Worked backwards from my resistor simplifications. When the resistors were in...
  13. J

    Engineering Voltage across the output resistor for this opamp circuit

    Here is question: Find voltage across R3 options: 10V 11V 5V 2V Attempt: No current flows through Opamp, so 1mA flows through R3, this gives voltage across R3 = 1ma * 1K = 1V. But that is not in option. Where am I wrong? No current flows inside or outside opamp, right?
  14. 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...
  15. P

    New Parallel Resistor Calculation Method

    In teaching HS Physics part of which is Electric Circuits, I have discovered a rule / technique for parallel resistors that I never encountered in all my 30+ years in electronics engineering, nor in any textbook on Circuits. It is what I call " The N + 1 Rule " We all know the Reciprocal...
  16. Eucliwood

    Calculating Resistance at Multiple Points in a Resistor Network

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  17. C

    Avalanche relaxation oscillator biasing resistor

    I've tried the circuit in this article. It works very well and I've obtained 2ns clear pulses at 150 V (the main issue was to find the right avalanche voltage, which turned out to be 150-160V for my 2n3904 transistor). While the basic principles of operation in this circuit is clear for me, I...
  18. Tesladude

    What is the voltage across this capacitor, inductor and resistor?

    I can solve for the questions in completely series or parallel circuits however having the capacitor and inductor in parallel while the resistor stays in series is stumping me completely.
  19. M

    Coil and resistor in parallel -- How to calculate the phase angle?

    Hello. So I have a coil and a resistor in parallel connection. It is powered by alternating current. I have to calculate angle between voltage and current, what is the formula? I know the reactive resistance in coil, I know resistance of resistor, voltage across both of them and amps flowing...
  20. 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...
  21. P

    Finding the current and voltage for each resistor

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  22. MedEx

    Finding the Current in a Resistor in a Closed Circuit

    1. Homework Statement The ideal battery in Figure (a) has emf = 7.7 V. Plot 1 in Figure (b) gives the electric potential difference V that can appear across resistor 1 of the circuit versus the current i in that resistor. The scale of the V axis is set by Vs = 18.9 V, and the scale of the i...
  23. K

    B How a Secondary Resistor affects the Transformer Primary Side?

    Let's assume a 2:1 transformer which has a 100V Source connected on the primary circuit and has no/negligible resistance, on the secondary circuit a 5 Ohms resistor is connected. Using the 'Impedance Transfer/Reflection' method, the primary circuit would act as if there was a 25 Ohms resistor...
  24. R

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  25. S

    Measuring the resistance of a resistor

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  26. fluidistic

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  27. Eduardo Leon

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  28. marino

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  29. iVenky

    I Intrinsic impedance of a resistor

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  30. Lapse

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  31. M

    Is the Earth a Resistor or Capacitor for Underground Cable and Pipe Location?

    I work for a company that locates underground cables and pipes. We apply an AC signal to the underground facility and to be able to detect the location. Take the simplified drawing above. Two transformers grounded with a buried electrical cable. We use a transmitter and connect it to one...
  32. bornofflame

    RC Circuit - Rate energy is dissipated in the resistor

    Homework Statement 1. A 2.01 uFcapacitor that is initially uncharged is connected in series with a 6.51 kΩ resistor and an emf source with 74.6 V and negligible internal resistance. The circuit is completed at t = 0. a) Just after the circuit is completed, what is the rate at which electrical...
  33. F

    I Proof that the E field inside a cylindrical resistor is constant

    I am reading a proof for this statement and I don't understand one of the steps. It is stated that since the surrounding medium is nonconductive the flow of charge at the surface has no component along the normal of the surface. From this the conclusion is drawn that the E field along the normal...
  34. J

    Circuit with resistor, switch and capacitor

    Homework Statement We have a circuit with a battery, two resistors, a switch and a capacitor. We assume that the battery has a switch so that we can choose whether it should be a voltage source for the circuit. a) At time t = 0, we put on a voltage Vs over the battery in the circuit. What is...
  35. Muhammad Usman

    Pull Up resistor in the Voltage?

    Hi, May be this is the most basic question, but I don't understand the concept of pull up resistor and how they maintain the voltage value. For example let's take an example of below circuit. There is 5 volts battery and then there is 10K resistor which is further connected with the Vout which...
  36. G

    Spherical Capacitor Discharging Through Radial Resistor

    Homework Statement A spherical capacitor has internal radius ##a## and external radius ##b##. At time ##t = 0##, the charge of the capacitor is ##Q_0## Then the two shells are connected by a resistor in the radial direction of resistance ##R##. Find the Poynting vector and the energy...
  37. AchillesWrathfulLove

    When putting a Resistor in series with an LED

    When putting an LED in series with a Resistor do you put it according to current convention (positive to negative) or to the actual current flow? Does it matter?
  38. C

    Energy dissipated by resistor problem

    Homework Statement A 10 Ω resistor carries a current that varies as a function of time as shown. How much energy has been dissipated by the resistor after 5 s? a. 40 J b. 50 J c. 80 J d. 120 J Homework Equations I=dq/dt → dq=Idt → Q=∫Idt P=∇E/∇t and V=IR (Ohm's Law) so P=IV ⇒...
  39. 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...
  40. F

    Engineering Unknown resistor in a series-parallel circuit

    Hey guys, I have tried and tried to find a start to this problem with no success. My book may have the answer but unfortunately I must be not realizing it. So hopefully I just need a different perspective. Typically I would find the equivalent resistance of the circuit and then begin to...
  41. 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...
  42. H

    Find the transient current in this circuit

    Homework Statement Homework EquationsThe 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 please...
  43. C

    RC Circuit with parallel resistor

    Homework Statement A circuit contains a capacitor of capacitance C, a power supply of emf E, two resistors of resistances R1 and R2 , and a switch S2 . Resistor R1 is in series with the power supply and R2 is in parallel with the capacitor and the power supply. S2 switches the branch that...
  44. P

    Potential difference across a resistor

    Homework Statement Two cells of same emf E and different internal resistance r1 and r2 are connected in series to an external resistance R.The value of R for which the potential difference across the first cell is zero is given by (A) R=r1/r2 (B)R=r1+r2 (C)R=r1-r2 (D)R=r1r2 Homework Equations...
  45. F

    What causes a voltage drop over a resistor?

    Why is the electrical potential greater before it passes through a resistor than after?
  46. J

    Does the current increase or decrease through the resistor ?

    Homework Statement Homework EquationsThe Attempt at a Solution This looks to be a simple problem but the answer key has left me wondering whether I am thinking correctly . I get option 1) whereas answer key states option 3) . Since the variable resistance R increases , the resistance...
  47. A

    Power dissipated by a Resistor

    Homework Statement What power is dissipated by the R2=3.0Ω resistor in the figure if R1=6.0Ω? Battery 1: 12 V Battery 2: 15 V Resistor 1: 3.0 Ω Resistor 2: 6.0 Ω Homework Equations P = V2/R Rtotal = R1 + R2 The Attempt at a Solution I started on the left side and used the formula, P = V2/R...
  48. 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...
  49. 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...
  50. J

    Power dissipated in a resistor

    Homework Statement Homework EquationsThe Attempt at a Solution Power dissipated in the 2 Ohms resistor will be maximum when current is maximum .This will occur when total resistance is minimum . If I think logically then I do get the right answer . But on trying to arrive at the result...
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