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. C

    Engineering Load resistor in circuit: Find the no-load voltage.

    Homework Statement http://imageshack.us/a/img62/5467/homeworkprob14.jpg A. Find the no-load voltage of V0 B. Find Vo when RL is 450 kΩ C. How much power is dissipated in the 30 kΩ resistor if the load terminals are accidentally short circuited D. What is the maximum power dissipated in...
  2. J

    Engineering Calculating when voltage across resistor = voltage across inductor in an RL circuit

    Homework Statement A step input of 100V is applied to a resistor of 50Ω in series with an inductor of 10H at time t=0. Calculate the time at which the voltage across the resistor equals the voltage across the inductor Homework Equations Im not sure which equation to use, i know τ=L/R...
  3. A

    Power dissipated by a resistor in parallel

    Homework Statement We are given a circuit as follows: V= 10 V and two resistors are in parallel. R1 is 12 ohms and R2 is 5 ohms. What is the power dissipated in the 12 ohm resistor? Homework Equations V=IR P=(I^2)R The Attempt at a Solution I know that the total resistance of...
  4. L

    Expression for voltage across resistor in circuit

    Homework Statement Write an expression for the voltage across R3 in terms of V0, R1, R2, and R3. Under what condition is the voltage across R3 approximately independent of the value of R3? Homework Equations I uploaded a picture. I think Req = R1 + R2... and 1/Req = 1/R1 + 1/R2...
  5. G

    Determining resistance of a series resistor in a simple series circuit

    Background: I learned electronic theory 10 years ago from the Army, and have since worked in the electronics industry as a technician, for about the past 9 years. I'm working towards a BSEET (my interest lies in application, not research) and am required to take a few algebra based physics...
  6. V

    How Does Symmetry Solve a Cubic Resistor Network?

    Dear all, I'm trying to understand the second figure of the following webpage. The webpage simply solve it by 'symmetry', but I could not figure out its reasoning. Could someone explain how does it work? Thanks in advance...
  7. S

    Calculating Voltage and Current after resistor from an Arduino Uno.

    I have an Arduino Uno micro controller that operates at 5V and I'm doing some work with an LED. The positive leg of the LED has a 220ohm (1/4watt) resistor on it and goes into output pin 13 which produces 40ma @ 5V. My LED wants to have 2V @ 18ma. I'm not quite sure yet how to calculate the...
  8. I

    Is current reduced in a resistor?

    Everyone knows the classic series circuit rule that states that current is the same everywhere, but is this also true in the resistors or a load, like a light bulb filament? I would think that the resistance caused by the electrons smashing against the atomic nucleii in the conductor would...
  9. H

    Analysis for calculating Ideal Opamp current without resistor

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  10. A

    Doubting Ohm's Law: LED & 220Ω Resistor

    As the title states I am really doubting Ohm's law. This is why: On a breadboard I placed a white LED and a 220Ω resistor with the 9v battery all in series. The total current flowing through the circuit shouldn't be more than 41mA by V=IR, but my multimeter points between the range of...
  11. P

    Temperature of resistor in latent heat experiment.

    Hi, I have conducted an experiment for finding the latent heat of liquid nitrogen using a 5W power supply and a 200 ohms resistor. As part of my conclusions I am asked to discuss/refer to the resistor's temperature during the experiment. I am not sure whether I am expected to provide a...
  12. Q

    Calculating the value of R for a resistor in an RLC series circuit

    1. An RLC series circuit has C= 4.8mF, L=0.520H, and source voltage amplitude V= 56.0V. The source is operated at the resonance frequency of the circuit. If the voltage across the capacitor has amplitude 80.0V, what is the vaule of R for the resistor? 2. ##I = (ΔVc)/(Xc)##, ##Xc=...
  13. A

    Can a material have both dielectric and resistance properties?

    Hi, Do material posses both dielectric as well as resistance properties? I imagine that when there is a difference in potential across a volume of some material, some current will flow (I=V/R <-- the material's resistance), but also the material may become polarized to a certain degree...
  14. T

    How Does AC Power Flow Through a Resistor, Inductor, and Capacitor in a Circuit?

    Homework Statement A circuit is constructed with an AC generator, a resistor, capacitor, and inductor as shown. The generator voltage varies in time ε=Vb-Va=εm cos(ωt), where εm = 122.5 V and ω = 10.35 x 106 radians/second. The resistance of the circuit is R= 132.1 Ω. The inductance is L=...
  15. F

    Using a shunt resistor for measuring current

    I was using a signal generator to perform some tests. The circuit was simply the generator in series with a 1 ohm shunt resistor. Even though I was working with high frequencies (1 to 20 MHz), shouldn't the voltage drop across the resistor be the generator amplitude itself? I was using the...
  16. C

    AC vs DC power loss across a resistor

    I was recently informed that AC is the preferred method of transmitting power because it suffers significantly less power loss going from the generating station to where ever it needs to go when compared to DC losses. In my introductory electricity class we learned that power through a given...
  17. W

    Finding the current in a resistor

    Homework Statement I have the picture attached. Homework Equations I = V/R The Attempt at a Solution I labelled the 2ohm and the 1ohm resisters in series (R1 and R2). Labelled 5ohm and 1 ohm in series R3, R4. So i found the Req So R1 and R2 are in series so add them 2+1 =...
  18. J

    Simplifying Complex Resistor Circuits

    Simplifying "Complex" Resistor Circuits Homework Statement Question 1: I have an E&M test coming up and I'm having trouble simplifying complex circuits. Our teacher told us something about "pinching" the wires which I didn't really understand. I found the following link...
  19. M

    Why is a current limiting resistor necessary in an LED circuit?

    Let's say that I have an LED where If=20mA and Vf(typ)=2v. I want to power it directly with a 2v lead acid battery. According to most answers to this question I have read this will either not work (with the outcome unspecified), will destroy the LED, or is just a bad idea because of how an ideal...
  20. M

    Series Resistor Problem: Finding the Equivalent Resistance

    Homework Statement Homework Equations The Attempt at a Solution What I did was I knew that the their are two resistors in series 1/req= 1/R + 1/R = 1/2R req= 2R Where I get confused is how do I include the other resistor since I believe that it is in series?
  21. C

    Engineering Simplifying Complex Resistor Circuits

    Homework Statement See attached image. Homework Equations The Attempt at a Solution I cannot find any resistors in parallel or series in the circuit. I am confused by the lone branch going from the 10kOhm resistor back to the other end of the same resistor. How do I deal with...
  22. A

    Find Resistance R_AB: Learn How to Solve the Question

    I can't seem to get the right answer for this question I am thinking (250+470) in parallel with 940. Can someone please explain me this question?
  23. N

    Electric potential difference across capacitor and resistor

    Homework Statement In the circuit shown a resistor of 200k ohm is in series with a capacitor of 500uF and a 9v battery. Switch closed at t=0. What is the electric potential difference across the capacitor and the resistor at t=100? Homework Equations Q=cv Tau=rc Q=q(1-e^t/rc)...
  24. B

    Resistor and Current Source in Parallel with Short Circuit?

    This circuit is really confusing me. I'm trying to find i using KVL and KCL. What's throwing me off is the short circuit effectively created by the inductor. I know that the whole circuit can't be short circuited because there is a current source that is preventing all of i from going through...
  25. J

    FFT and Resistor Noise Newbie Questions - PLEASE HELP

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  26. S

    Understanding RC Circuit Currents: A Homework Question

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  27. Y

    Two ideal dc sources and a resistor with lengths involved

    Ive been given an assignment with the question being question 13of the following pdf: http://vlsi-eda.cm.nctu.edu.tw/course/ICT_12Summer/hw/HWCh4.pdf (note this isn't my actual assignment i just found this one on the internet that happened to be the same question that i was looking for) Im...
  28. D

    Engineering Voltmeter in simple battery + resistor circuit

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  29. E

    Thevenin circuit Max power across Load resistor

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  30. D

    Can Resistors Be Used in A/C Circuits?

    I thought that resistors, like the ones that I buy at RadioShack, could only be used on D/C circuits. I was looking up how to's on electromagnets and found a thread that mentioned using resistors with A/C power. The thread was on this forum but I can't find it now. I am guessing that the...
  31. A

    Calculate New Power when adding a Resistor

    As this is my first post please feel free to correct me if I am posting this is the wrong section or on improper etiquette in general. I'm having a bit of trouble with what should be a pretty simple problem. Homework Statement A resistor R1 = 23Ω is connected to a battery that has negligible...
  32. P

    Finding the current through a resistor using superposition theorem.

    Homework Statement We have this circuit. The problem states to find i, or the current through the 3 ohm resistor. Homework Equations V = IRThe Attempt at a Solution I've started by shorting out both voltage sources and leaving only the current source in the circuit. I paralleled the 4ohm...
  33. A

    Determining the current through a resistor

    Consider the circuit drawn on the attached picture. I have seen a calculation of what the current through each of the resistors is using Kirchoffs laws. Unfortunately I don't qualitatively understand how you are able to determine the current through them. First of all, but this is probably...
  34. C

    Resistor values of LED, LCD, Processors

    I have a generator which after being regulated, outputs 70mA through 3V. (I should say the amps go through the voltage right?) In some circuits I may be using diodes. Some advice me that the voltage drop is 0,7. Others say it's dynamic, that I should divide the driving voltage over the...
  35. A

    Current through the circuit with resistor and light bulb

    Homework Statement Problem is give in the image Homework Equations V=IR The Attempt at a Solution Since its a series circuit i tried that current should be the same so it's 9/20 since there is no resistance in the bulb which is 0.45 Ω somehow the answer is 0.3Ω. why is that the...
  36. H

    Resistor is a current limiting element.?

    In a simple circuit having battery (6v) connected to two resistors (1K each) in series, 3mA would flow through the entire circuit. 1) If resistor is a current limiting element, current following the first resistor should reduce its value (from 3mA to some other) before entering the another...
  37. S

    Calculate the current through the 22ohm resistor (Kirchhoff's Rules)

    From the image attached: A. Calculate the current through the 22Ω resistor. B. What is the voltage across ab Here is what I've done: A. ) I labelled the currents and applied the Junction Rule I1 + I2 = I3 -I1*22Ω + 8V + 13*6Ω + 18V - I3*6Ω = 0 -I1*22Ω + 8V + I2*14Ω - 12V = 0...
  38. M

    Diode running into the resistor

    http://www.itisff.it/dip_eln/tda2030.pdf Couple questions. 1. In the Typical Application diagram on the left there is Vi w/ a 22k resistor. Appears that there's a diode running into the resistor and then the resistor goes to ground. The question is how should I interpret that? The...
  39. O

    Variable Resistor connected to parallel resistors

    Homework Statement In the electric circuit shown in the figure, when the value of the variable resistor R3 is 25Ω, the current which flows into the power supply is 2A. Moreover, when the value of the variable resistor R3 is 5Ω a current of 1A flows into the resistance R2. Q1.Find the value of...
  40. JJBladester

    Simplifying a resistor network using pi-T (Y-delta) conversion

    Homework Statement Reduce the resistor network to a single resistor. Go step-by-step and indicate the series or parallel combinations being reduced. Homework Equations For series resistors: R_T=R_1+R_2+R_3+\cdot \cdot \cdot +R_N For parallel resistors...
  41. B

    Energy Dissipation Across a Resistor

    Homework Statement A battery is connected across a uniform resistor R0. A sliding contact can move across R0 from x=0 to x=10cm at the right. Moving the contact changes how much resistance R is to the left of the contact and how much is to the right. Find the rate at which energy is dissipated...
  42. L

    Resistor Temp Variation: 2K at 0°C or Room Temp?

    Every resistor has some variation with temperature. Let's say I pick a 2K resistor. Is the 2kohm specified at 0 deg C or room temp?
  43. K

    How do I find the emf and internal resistor of this cell of this circuit?

    This is a potentiometer circuit. I don't have the diagram so I hope you can follow me. This is the main circuit with the unknown emf E with internal resistance r of the main cell and with two resistors P and Q connected in series at the bottom of this rectangular circuit, p being connected near...
  44. B

    Understanding Resistor Volt Drops

    I've come across a booklet on understanding electricity, and it's been very interesting, but I've hit a rut! The packet says that the sum of the voltage drops of resistors equals the source voltage. How is that possible? Were the voltage to continuously drop, wouldn't no voltage exist at all...
  45. J

    Total Current Draw Of LED And Resistor Combined

    I am using a 3.3 volt led rated 25 ma powered with 12 volts and have 1000 ohm resistor in between. Ohms law says amps = ohms / volts so 12 / 1000 = 12 ma so is this all the LED and resistor combined will draw? As I know the led can only handle 25 ma, but if the led where using this much current...
  46. S

    What is a Resistor & What Does it Do?

    and what is its purpose? what does a resistor actually do? My understanding is that electrical resistance is sort of like electrical friction, or imagine sitting in a car, with your hand out of the window, as the car speeds up, you feel more resistance against your hand, and it takes...
  47. J

    Charging capacitor - no resistor

    Homework Statement When charging a capacitor with NO resistor in the circuit, the p.d of the capacitor IMMIDIATELY reaches a maximum... Homework Equations The Attempt at a Solution ...is the following reasoning correct: As stated by Kirchoff's Law, the sum of the potential differences...
  48. A

    R1 + R2 in Parallel with R3 + R4 + R5 in Series | Find Req

    Homework Statement Five resistors with resistance R1 = 4.00 Ω, R2 = 6.00 Ω, R3 = 2.00 Ω, R4 = 7.00 Ω, R5 = 4.00 Ω, are connected to a battery with emf = 8.00 Volts as shown in the figure. Find the equivalent resistance of the circuit. Give you answer with a unit of "Ohm". Homework...
  49. I

    [Confuse]Capacitor and resistor in DC circuit,

    [Confuse!]Capacitor and resistor in DC circuit, please help :) Homework Statement The figure in attached file below shows a circuit in which a battery (electromotive force = 10V) is connected with three capacitors (capacitance = 1 microFarad, 2microFarad,3microFarad) and two resistors...
  50. F

    Engineering Need help with 2 capacitor 2 resistor circuit

    Homework Statement Find an expression for Vo, the voltage across the resistor. Hint: find V1 and V2 first.Homework Equations i_c = C(dV/dt) V_c = 1/C integral( i dt )The Attempt at a Solution I think at t = 0, the voltage source turns on so @ t < 0 : V1(0-) = 0 V2(0-) = 0 @ t > 0 ...
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