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. J

    UV LED circuit - how many and which resistor?

    Many years having passed since I last looked at an electrical circuit, I been asked to design an electrical circuit at work. We make tonic water, and the idea is to create a holder for bottles with a built-in UV light rigging. Due to the relative efficiency, robustness, cheapness etc, I am...
  2. Femme_physics

    Understanding Vout: How to Properly Calculate and Discount Resistors

    In trying to figure out what's Vout, do I discount R4? I don't believe any current will flow through there. http://img825.imageshack.us/img825/7236/vinvout.jpg
  3. I

    Platinum Resistor: Measuring Temperature with High Accuracy

    Homework Statement A Pt-resistance thermometer is used to measure temperatures in the range 0°C to 100°C. The electrical resistance of the thermometer is 2 Ω at 20°C and 6 Ω at 100°C. It is necessary to measure the temperature to an accuracy of ± 0.1 K. How accurately must the electrical...
  4. J

    Transistor as a variable resistor

    I am looking to design a circuit, most likely with a transistor, to act as a voltage controlled rheostat. The controlling voltage can range from 0 - 3.3 v and I am trying to get a resistance range of about 200 - 5500 ohms. The circuit should have fairly high input impedance since it will be...
  5. L

    Deriving the damped circuit equation and energy dissipated through a resistor.

    Homework Statement I figure I will just combine these two questions into one topic. 1) The energy stored in a capacitor is .5CE^2, where E is the voltage. Wat is the instantaneous power dissipated in a resistor R through which this capacitor discharges? Show that the total energy dissipated...
  6. L

    Find the Current passing through the Resistor.

    Hi, forum. This is my first time posting and I was curious if someone would mind looking over my work for a problem? I need to find the current passing through R1 and R5, the picture below shows the problem and my attempt at a solution. In the picture there are three main equations I used...
  7. R

    Engineering Solving a Circuit with Diodes: Find V Across Resistor

    Homework Statement http://img832.imageshack.us/img832/6302/20285200.jpg Uploaded with ImageShack.us Homework Equations The Attempt at a Solution I'm unsure where to begin with this. I need to find the value V across the resistor and I'm unsure how. What effect do the diodes...
  8. E

    What happens to the speed of charge carriers when going through a resistor

    Hi everyone, I hope this question hasn't be asked and answered already in this forum, I searched through all related threads but I couldn't find an answer specific enough to my question. Consider a simple circuit with a DC battery and resistor. When the electrons (the charge carriers in...
  9. F

    What Happens to Op-Amp Gain When Switch is On?

    http://img684.imageshack.us/img684/8362/opamp2.png Lets say we are given a non-inverting Op-Amp The gain of this circuit would be A = 1 + (R1+R2)/R3 if the switch is off. What happens when the switch is turned on? It shorts the R1 and R2 resistors am I correct? Does this mean that R1...
  10. L

    Can I adjust R4 and R5 to maintain a 12k input impedance?

    How do I reduce this resistor network. The input current and the return current should be equal. But in this case, some current will also flow to ground. Can't get my head around this.
  11. I

    Changing voltmeter resistor value

    I am try to measure the voltage from a high impedance source with a regular voltmeter with an input impedance of 10 mega ohm. But the voltage being measured is inaccurate. Is it possible to change the resistor value inside the voltmeter to 100 mega ohms to get a more accurate reading?
  12. G

    Finding current in a dual battery, triple resistor circuit.

    Homework Statement Find the current in each branch of the circuit shown in the diagram (attached) if: V1 = 1V V2 = 4V R1 = 1\Omega R2 = 2\Omega R3 = 1\Omega Homework Equations V=I*R The Attempt at a Solution Okay, so I know that the voltage will be even across the parallel...
  13. C

    Given I, find V across the elements (resistor, inductor, and capacitor)

    Homework Statement The current after t=0 in a single circuit element is as shown in Fig. 2-37. Find the voltage across the element at t=6.5\mu s, if the element is (a) 10 k\Omega, (b) 15 mH, (c) 0.3 nF with Q(0)=0. Ans. (a) 25 V; (b) -75 V; (c) 81.3 V...
  14. G

    Compute percent uncertainty of Resistor

    Homework Statement The relationship between resistance with temperature is expressed by the equation of R= R0[1+ α(T-T0)], where Ro is the resistance at the reference temp. T0 and α for the resistor material has been determined to be 0.0048 ± 0.1% oC. In the range 0 to 100* C, in which we...
  15. N

    Purpose of series resistor in parallel (R')RLC circuit

    Hi, I've understood the basics of an RLC circuit but it seems that when actually putting them into practice I'm advised to put an additional resistor in before the (RL) and C that are in parallel with one another with no explanation. What's the purpose of this resistor and what does altering its...
  16. S

    Calculating Current for Two-port Resistor Network

    Homework Statement A network of resistors has a pair of input terminals AB connected to a dc supply and a pair of output terminals CD connected to a load resistor of 120 ohm. The resistances of the network are AC=BD =180 ohm, and AD=BC=80 ohm. Find the ratio of the current in the load...
  17. P

    Voltage amplitudes across inductor and resistor

    Homework Statement A series combination of a 22.0 mH inductor and a 145.0 ohm resistor are connected across the output terminal of an ac generator with peak voltage 1.2 kV. (a) At f= 1250 Hz, what are the voltage amplitudes across the inductor and across the resistor? (b) Do the voltage...
  18. S

    Discharging a capacitor through a resistor

    Homework Statement A 2 micro F capacitor with an initial charge of 5.1 micro C is discharged through a 1.3 kohm resistor a) calculate the current though the resistor 9ms after the resistor is connected across the terminals of the capacitor. b) what charge remains on the capacitor after 8ms...
  19. S

    Current in circuit with resistor and two batteries

    Homework Statement what is the current in each of the branches in this circuit: [PLAIN]http://img593.imageshack.us/img593/893/resisotrcurrentquestion.th.jpg http://img593.imageshack.us/i/resisotrcurrentquestion.jpg/ Homework Equations v=ir r1+r2 = r3 1/r1 + 1/r2 = 1/r3 v1 + v2 = v3 ? The...
  20. H

    Wire-Wound Resistor Calculation - 18.6 Ohms/m

    Homework Statement A long, insulated wire with a resistance of 18.6 ohms/m is to be used to construct a resistor. First, the wire is bent in half, and then the doubled wire is wound in a cylindrical form as shown in the above figure. The diameter of the cylindrical form is 2.6 cm, its length is...
  21. I

    Current sensing and standard resistor

    I have a 12v switching transformer; one of the legs on a black brown silver gold 2w resistor is broken off. I have had zero luck finding a standard .01 2w resistor. I did find a current sensing resistor at the values, but should it be used. The resistor in the power supply is ceramic, I think...
  22. P

    Voltage drop across a resistor in a circuit

    Homework Statement Three batteries and four resistors are connected in a loop as shown (see attachment). What is the voltage drop across the top left resistor? Homework Equations V = IR The Attempt at a Solution This is part 3 of the 3 questions for this problem. On the other...
  23. M

    Capacitor - Resistor || Capacitor - Capacitor AC circuit

    An AC circuit consists of 3 segments: a capacitor, then another capacitor which is in parallel with a resistor, and then finally another capacitor, these 3 segments being in series with each other. The formula which describes the charge Q(t) on the left hand side plate of the first capacitor...
  24. B

    Transfrom scheme into eq. scheme with one EMF and one resistor.

    I don't know English well(I'm from russian speaking countries) but I try to explain the problem(and practise my english too) Homework Statement Transfrom scheme into eq. scheme with one EMF and one resistor. Homework Equations Where is the series configuration of resistors and where is...
  25. I

    Understanding Power Dissipation in Parallel Resistors

    Ok, I'm not an EE student, nor do I really understand all of the P=IE^2 stuff concerning power and resistance, etc. My question is regarding the power dissipation abilities of resistors in paralell. Let's say I have (10) 100ohm/5w resistors in paralell. Would this effectively be a 10ohm load...
  26. C

    Calculating Resistance of 25W Lamp & Resistor in Series

    Homework Statement a) Bulb power is 25 W 24 V voltage. b) 25-watt light bulb and resistor, whose resistance is 19 Ω, connected in series and connected to 24 V DC voltage. In this case, passing within 0.71 A of current. Homework Equations a) Calculate the resistance of the lamp. b)...
  27. K

    Is a Shunt Resistor Necessary for a 12VDC, 40W Electromagnet Setup?

    I have a 12vdc, 5Amp power supply and need to connect to a 12vdc, 40 watt electromagnet. I put a SPDT relay switch between the power supply and the electromagnet to turn it on and off. Do I need to put in a shunt resistor or something else to protect the magnet and the power supply? How do I...
  28. S

    Parallel Circuit 2 batteries, solving for current of resistor

    Homework Statement For the circuit shown in the figure below, calculate the current I4 through the 2.18 resistor. As shown, R1 = 4.20 R2 = 8.12 R3 = 6.10 R4 = 2.18 I1 = 3.16A and E1 = 18V I couldn't get the picture on here but I will describe it: It is a parallel circuit, with...
  29. A

    Current through a resistor in a network

    Homework Statement Consider the electric circuit shown in the figure. Assume that V = 21.7 V, R1 = R2 = R3 = R4 = R5 = 6.00 Ohm. Part 1) What is the equivalent resistance of the circuit? Part 2) what is the electric current flowing through R4? Homework Equations Series and parallel...
  30. U

    Sum of potentials across a resistor in series with parallel RC

    Homework Statement We have built a circuit with an ac source containing a resistor in series with a parallel RC combination, we have measured the voltage across the first resistor and the voltage across the RC combination with a high and a low frequency. 80Hz: V0 = 2,325 V en Vm = 2,780 V...
  31. N

    Calculating the currents in each resistor

    Homework Statement Calculate the currents in each resistor in this figure: http://session.masteringphysics.com/problemAsset/1084690/2/GIANCOLI.ch26.p32.jpg Homework Equations Kirchhoff's rules In a closed loop: the sum of voltage is 0 A a junction: the sum of current is 0 The...
  32. A

    How to Calculate Equivalent Resistance in a Series-Parallel Circuit

    Homework Statement Find the equivalent resistance of the circuit as shown in the diagram below; where R1 = 4.0 , R2 = 3.0 , R3 = 1.0 , R4 = 3.0 , R5 = 2.0 , R6 = 4.0 , and R7 = 1.0 . [Ohm] Homework Equations Parallel and series resistance equivalence Req= 1/R1 + 1/R2 + 1/R3 ... etc...
  33. S

    What is the current in each resistor and the power delivered by the battery?

    Homework Statement The battery has negligible internal resistance http://www.webassign.net/tipler/26-50.gif Find the current in each resistor. Find the power delivered by the battery. Homework Equations V=I/R P=IV The Attempt at a Solution Now I feel like this problem is ridiculously simple...
  34. I

    Correcting Voltage Drop by Adding Resistor L Pad

    I have a source of 800 Kilo Ohms and I want to power an LED with that source. Which I would presume the LED would have a resistance of 9.5 to 10 Ohms if I'm correct. When I connect the LED to the source the voltage drops from 12 volts DC to around 1 volts DC. If my thinking is correct the reason...
  35. T

    Are These Resistor Problem Calculations Correct?

    Homework Statement http://img214.imageshack.us/i/124w.png/ Homework Equations \[R = \frac{V}{I}\] P=VI The Attempt at a Solution a) Using KVL around the loop, I got V_{R}=6.3 V . Then I used \R = \frac{V}{I}\ and got R = 1.4 ohms. b)I used P=VI and got P = 28.35 W...
  36. H

    Engineering Ac circuit non inductive resistor and a coil

    Homework Statement A non inductive resistor takes 8A at 100 volts. What inductance of a coil of negligible resistance must be connected in series in order that this load can be supplied from a 220 volt 60 Hz mains. Homework Equations Z^2 = R^2 + XL^2 R=V/I XL = 2pi(frequency)...
  37. N

    Are the Req's between Two Nodes Equivalent? Basic Resistor Question Explained

    Are the following Req's between the two nodes equivalent? I'm pretty sure the first and seconds ones are, sort of sure the third is, and a little sure the fourth one is. The r's are the resistors. I'm sorry that the pictures are so crude, I couldn't attach my MS paint picture's jpeg or png Bonus...
  38. R

    Voltage vs Current curve isnt going through origin for Playdoh resistor, why?

    Hi, I'm doing a IB Physics internal assessment on how the length of a tube of playdoh in a straw relates to the resistance of that tube. I tested it by connecting a 150 ohm resistor to one end of the tube of playdoh and connected the two to a power supply. My data at the different lengths all...
  39. C

    Calculating Resistance of Resistor for 12V/10W Lamp & 24V Accumulator

    Homework Statement A lamp is marked 12V/10W. the lamp is connected to 24V accumulator. in series with lamp you must then connect a resistor. Calculate the resistance of the resistor. Homework Equations The Attempt at a Solution
  40. S

    Solution to Op-Amp Circuit with Adjustable Resistor RΔ

    Homework Statement The op-amp in the circuit shown is ideal (please see attachment). The adjustable resistor RΔ has a maximum value of 160 kΩ and α is restricted to the range of 0.22 ≤ α ≤ 0.7. (a) Calculate the range of vo if vg = 40 mV (b) If α is not restricted, at what value of α...
  41. M

    Resistor Shorting and Kirchhoff's Rule Explanation

    Homework Statement What would the current I1 be in the figure below if the 18 Ω resistor is shorted out (resistance = 0)? Let r = 1.0 Ω. Homework Equations I used Kirchhoff's RuleThe Attempt at a Solution I figured this problem out, but I had trouble, and I'm not sure I understand why the...
  42. B

    Energy dissipated as heat during a time interval over resistor with constant pot. dif

    Homework Statement How much energy is dissipated as heat over 2 minute time interval by a 1.5 k(ohm) resistor which has a constant 20 V potential difference across its leads? Homework Equations deltaV=-Ed The Attempt at a Solution In my notes this is the only equation that seems...
  43. P

    Assorted Resistor and Capacitor

    Anyone could suggest which resistor and capacitor value that used most in home-brew project? Those project basically deal with LED and PIC. I want to buy them in bulk, but I do not know how to assort them. I wish to buy like 50 resistors and 50 capacitors. Looking forward for your help.:)
  44. T

    What is the purpose of connecting a resistor in the circuit?

    When charging the capacitor, what is the purpose of connecting a resistor in the circuit? Is it to slow down the rate of charge entering the capacitor, therefore lowering the potential difference across it? I think that doesn't make sense. Or maybe to encourage the flow of current in the...
  45. A

    Rms current in circuit with capacitor resistor and rms output

    Homework Statement A 39.5 uF capacitor is connected to a 47.0 ohm resistor and a generator whose rms output is 25.2 V at 60.0 Hz. Calculate the rms current in the circuit. (also asks for voltage drop across resistor, capacitor and the phase angle for the circuit, but I mostly want to get...
  46. S

    How Can Increasing Resistance Affect Voltage and Current?

    how can i increase the voltage, without changing the current... do i increse the current or decrease it V=IR--->(V/R)=I i just increase the resistance
  47. M

    Is this Resistor Capacitor Circuit Reliable and Versatile?

    http://www.mediafire.com/?dqjlrfbu0m63l67 Hey I've been trying to recreate this circuit on a breadboard for a while and it never works... Then I try to make it in a circuit simulator and it still doesn't work. Anyone know if the circuit actually works? Also I believe this circuit can be used...
  48. C

    Capacitor charging with unknown resistor

    Homework Statement Capacitor voltage as a function of time is recorded for a simple direct current RC series charging capacitor. How could we determine the resistance of the resistor?Homework Equations q=Qe^\frac{-t}{RC}The Attempt at a Solution I understand the question I'm just having...
  49. G

    Capacitor in parallel with resistor

    (another problem but less differential equations-sy) Consider a circuit where there is an effective resistor in parallel with an effective capacitor. Each effective capacitor consists of two capacitors in series, same for the resistor. Now, when the capacitors are uncharged, all the...
  50. G

    Calculating Time Constant and Effective Resistance for a Parallel RC Circuit

    I am trying obtain some equations for an RC circuit that has a resistor R1 after a battery, which then splits into a capacitor C and a resistor R2 (the circuit closes after this point). When I try to seek help online, the resources are quite unhelpful. I cannot seem for example, obtain any...
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