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. T

    Effect of frequency of a.c. circuit, resonance and temperature in resistor

    In an L-R-C circuit, if the reactance of the capacitor equals that of the inductor, X_L = X_C, and consequently the current is at it's max and we have resonance, will the temperature in a resistor with a positive temperature coefficient increase faster in this situation, and thus get increasing...
  2. T

    Why Does a Resistor Show Different Values in AC and DC Measurements?

    Homework Statement If possible, find reasons why the resistance of a resistor may have a different value when measured with a sine wave signal (a.c.) than when measured with a d.c. (dirrect current) source. Homework Equations The Attempt at a Solution Please correct me if anything...
  3. P

    Engineering Linear Circuit - current through Load Resistor

    Homework Statement When a 2-kΩ load is connected to the terminals A–B of the network in the figure, the current through the load is IL = 10 mA. If a 10-kΩ load is connected to the terminals, IL = 6 mA. Find IL if a 20-kΩ load is connected to the terminals. 2. The attempt at a solution I...
  4. xortan

    Calculators Resistor Calculator - C - Complete n00b

    Hi all, I am studying to be an electrical engineer and I have a C programming course that all of a sudden took a massive jump..last week we were writing single For statements and things of that manner and now he assigned a program that's just got my completely stumped, I thought I was...
  5. R

    How to Find the Current in a 6 Ohm Resistor?

    hello Find the power dissipated in the (6 ohm) resistor. the circuit is in the attachments i know that P in the resistor = (i^2)*R but how can i find the current in that 6 ohm resistor? thanks
  6. N

    Finding Length and Area of Tungsten Wire Resistor

    Homework Statement the actual question is the resitivity of tungsten metal is 4.9x10to the power of -6 Ωcm. choose appropriate values for length and cross-sectional area for a home made wire resistor of resitstance 20Ω Homework Equations r=pl/a r-resistance a-cross sectional area in...
  7. T

    Why Does a Light Bulb's Resistor Burn Out When Directly Connected to an Outlet?

    I was with my electrician friend the other day, and we stuck two copper wires into each of the holes of a regular 120V outlet then smashed a 100W light bulb and took the resistor (small coiled looking thing) out of it and set it on a piece of wood and touched the copper wires to each end of the...
  8. A

    Finding AC voltage across Resistor

    Homework Statement I have three questions 1. How do you find AC voltage across resistor when there are both AC and DC current? 2. is AC voltage across a resistor different from voltage across a resistor? 3. Find AC voltage across Resistor (in this image) http://img199.imageshack.us/i/acv.gif/...
  9. H

    Why is there resistor R2 connecting output and input of op amp?

    I have attached image. Thanks in advance.
  10. J

    Finding Voltage Across A Resistor in a 1st Order RC Circuit

    Homework Statement For the RC Circuit (R = 100 Ohm, C = 100 Micro Farads, and an open switch at t=0), we know that the capacitor is charged to a voltage of 10 V prior to T=0. Find expressions for Vc(t) and Vr(t). Homework Equations Vc(t) = Vi * e(-t/rc)The Attempt at a Solution Vc(t) =...
  11. K

    Potential difference across a resistor as measured by a voltmeter.

    Homework Statement The voltmeter shown in the figure below can be modeled as an ideal voltmeter (a voltmeter that has an infinite internal resistance) in parallel with a 11.0-MΩ resistor. Calculate the reading on the voltmeter for the following. R = 1.1 MΩ R = 10.8 MΩ R...
  12. L

    Really simple Resistor question NEED HELP

    So i have a general question that I came across with source transformations, but this question can be classed as a beginner question. When I find the equivalent resistance, how do you determine whether or not it is in series or parallel with a source?
  13. F

    Finding Scale Reading with New Resistor in Circuit

    The meter in the circuit shown in the image has an uncalibrated linear scale. With the circuit as shown, the scale reading is 20. Find the scale reading when another 2000Ω resistor is connected across XY.
  14. L

    Solving I3 Resistor Problem with Kirchhoff's Laws

    Find the current in I3 resistor by using kirchhoff's laws. problems: -when i try to use norton theorem to check for my answer and my answer is IN=2.855A=I3 but when i use kirchhoff's law i get I3=0.645A. -i don't know where is the problems...the current for norton theorem and kirchhoff's...
  15. R

    What is the reflection coefficient on a transmission line at a resistor halfway?

    Homework Statement If I have a coaxial transmission line, with a resistor halfway through, and another resistor at the end, how do I calculate the reflection coefficient for the spot where the resistor is halfway? Here is a diagram of what I mean. Dashes and dots are are the lines, and }...
  16. F

    How is a voltage drop across a resistor caused?

    Preface: Newbie here. Sorry if this has been asked before - I did have search but couldn't quite find what I was after. Also, I'm not putting this into the electrical engineering section because I don't want what will inevitably be an electrical engineer's answer =) Here goes: Voltage across...
  17. W

    Shunt resistor right application?

    I have a 400A (125VDC) charger that feeds a battery bank and a few DC panels (critical). This poor design has the panels being fed from the high side of a 600A breaker that is between the charger and battery bank. I need to take the battery off line for a load test but the problem I'm going to...
  18. J

    Uncertainty formula in resistor

    I am having a lot pf problem to attempt this question, please help me, i am stuck..! The power loss P in a resistor is calculated using the formula p=v^2/R The uncertainty in the potential difference V is 3% and the uncertainty in the resistance R is 2%. What is the Uncertainty in P...
  19. P

    AC Generator with Resistor: Exploring Kirchhoff's Loop Rule

    Homework Statement A resistor of resistance R is connected to an AC generator with EMF(t)=(EMF_max)sin((w_d)t). (a) Write Kirchhoff's Loop Rule for this circuit at a particular instant of time. Is your result a differential equation? (b) Find the current as a function of time. Now...
  20. P

    How Do You Calculate EMF in a Circuit with a Resistor?

    Homework Statement The question itself doesn't make sense to me, it says to find emf but the answer box has V= ? problem is an attachment. Homework Equations I=e/(r+R) Ir+IR=emf P=VI The Attempt at a Solution If it wants voltage that's simple P=I^2R P=V^2/R V=54.8V if...
  21. J

    Resistor to trick 12v transformer

    Hi guys, new here. I was wondering if anyone knew of a way to trick a 12 volt transformer into seeing more load. I have these lights http://www.lowes.com/pd_172832-24969-800CBL5N_0_?productId=1207073&Ntt=tiella&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=tiella$y=0$x=0" and it...
  22. R

    Complex current along a resistor

    If a current of .587e^j1.12 is passing along a 200ohms resistor, how would I go about calculating the power dissipated in the resistor?
  23. T

    Zener diode ballast resistor question

    Homework Statement Determine the value of the ballast resistor is satisfactory if a 5Volt 0.5 watt zener diode is used in the circuit sorry can't upload a picture but basically VS = 15v min to 20v max R ballast = 90 ohms (series with zener) and R load (in parralel with Zener) is 50...
  24. S

    Equivalent Current Through Specific Resistor

    Homework Statement http://farm5.static.flickr.com/4117/4775531139_8d4dd954f5_b.jpg Homework Equations I = V/R E = I1R2 = I2R2 =I3R3 The Attempt at a Solution I got 5.22 ohms for part (a), but I'm not sure how to go about calculating the amps through a specific resistor.
  25. P

    Electric current flowing through a resistor

    Homework Statement Consider the electric circuit shown in the figure. Assume that V = 10.4 V, R1 = R2 = R3 = R4 = R5 = 3.00 Ohm. What is the electric current flowing through resistor R2? I couldn't upload the figure, but you can find it on my cramster.com post...
  26. N

    Engineering Electrical Engineering- Capacitor Resistor Circuit

    Electrical Engineering-- Capacitor Resistor Circuit Homework Statement Hello all. First time posting so excuse any fourm faux pas I may make. I was wondering if anyone could lend some help with the circuit below (ignore the *, they are just space holders to prevent reformatting of the...
  27. C

    What is the current through the 10-ohm resistor?

    Homework Statement Number 15 http://lookpic.com/d2/i2/386/kFYE2mOH.jpeg [PLAIN]http://lookpic.com/d2/i2/386/kFYE2mOH.jpeg Homework Equations Rs=R1+R2+R3 Rpar=1/r1+1/r2+1/r3 I=V/R The Attempt at a Solution 1/(1/5+1/10+1/5)=2 Rtotal=7 I=21/7 I=3 I don't know what else to...
  28. Q

    Resistor Power Rating: What Does It Mean?

    i have a question about resistors. i thought they were described by their resistance - 20 ohm, 40 ohm, 2 Megaohm, etc. how come I see "power" values on resistors? for example my lightbulb says 40 watts. but i thought the power is simply P = V^2/R and that would depend the voltage of my power...
  29. S

    Simple logic diagram-with switch and resistor

    Homework Statement Why is it that the output is equal to V+ (when the switch is open) in diagram A, if there is no current flowing? Why is it that A (1/0) is used by convention? I mean the lamp I got at home has a "0" for off and "1" for on, on the switch. This is confusing me...
  30. jegues

    Resistor pattern - Equivalent resistance

    Homework Statement See figure Homework Equations Rs = R1 + R2 Rp = (R1*R2)/(R1+R2) The Attempt at a Solution I tried completing one repitition of the pattern to see if I could figure out what the Req would be so: R + R in series on the end so 2R // R so 2/3R in series with R...
  31. T

    How Does Angular Frequency Affect AC Voltage Across a Resistor?

    Homework Statement For the circuit below (attached) plot the amplitude of AC voltage across resistor as a function of the angular frequency of the ac source. Homework Equations ZR = R The Attempt at a Solution I'm not really sure about any of this. Across the resistor, the complex...
  32. C

    What is the resistance of a non-ohmic resistor in v-i graph

    What is the resistance of a non-ohmic resistor (lamp) in v-i graph given a voltage? I thought it would be the gradiant for specific voltages. But apparentlly it is the ratio of the specific voltage/current which makes sense too. So what is the correct out of the two?
  33. G

    How to calculate voltage at a specific resistor

    Homework Statement How would you calculate the voltage at a specific resistor given that it's a parallel circuit.
  34. K

    Resistor, capacitor and coil with Alternating current

    Homework Statement A problem from a translated Sears-Zemansky, 1965, 14-10: A conduction coil with inductance of 15 miliHenrys and resistance of 10 Ohms, is connected in line with a capacitor of 200 microFarads and a resistor of 12 Ohms. The circuit is supplied with an alternating current of...
  35. P

    Finding resistance of (semi-)infinite resistor chain between two points.

    Homework Statement What is the resistance of the (semi-)infinite resistor chain below, between points A and B, if R = 25 ohms? The Attempt at a Solution I am not sure where to begin exactly, but I am thinking of this formula: VAB=VB-VA=∑ε-∑i.R or...
  36. D

    Resistor Wattage: Find Out If You Need Bigger Resistor

    I have a circuit that uses a resistor to drop the input voltage. From my calculation, the power dissipation thru the resistor is less than it's wattage rating but yet the resistor is hot to the touch. Should I use a bigger resistor because it's too hot to the touch or should I keep using it...
  37. A

    Voltage drop and current for each resistor

    Homework Statement heres a picture of the problem. Please don't give me the answer just tell me what are the steps to complete it. thanks. http://i307.photobucket.com/albums/nn296/alan1592/download-1.jpg Homework Equations V=IR The Attempt at a Solution 1/6+1/3=2 Ohms
  38. S

    Resistor or Inductor: Exploring Rheostats

    Hi! A little food for thought for people who like high school physics labs.. In a standard rheostat(I have seen only the cylindrical one..the question is about rheostats of this shape..), we find a metal wire wound over a cylindrical core. The wire is wound with very closely spaced turns...
  39. T

    Resistor Nyquist-Johnson noise formula question

    Hi all -- I had a question about the Nyquist-Johnson noise formula: \[ E_{\nu}^{2}d\nu=\frac{4R_{\nu}hd\nu}{e^{h\nu/kT}-1}\] which of course can be approximated for most purposes as $ E_{\nu}^{2}d\nu=4R_{\nu}kTd\nu$. I'm just wondering why the formula has $ exp(h\nu/kT)-1$ in the...
  40. R

    Current source in series with resistor

    1. In the case of a current source in series with a resisitor, can this be transformed to just a current source with 0 resistance, or is the resistance infinity in the Norton equivalent? Homework Equations The Attempt at a Solution My teacher told us this in class but i can't...
  41. L

    What is the Potential Inside a Homogeneous Resistor?

    Homework Statement Determine the potential \phi inside a resistor of length l and radius a. Also determine the current density J, resistance R, surface and volume charge density Pe and Pes. The resistor is homogeneous. Homework Equations The Attempt at a Solution V=Ed, d=l here...
  42. Saladsamurai

    How can I find the current through R4 if the source voltage is known?

    Homework Statement Given that the souce voltage = Vo, find the Current at resistor 4. Homework Equations For resistors in series, I = constant For resistors in parallel V = constant The Attempt at a Solution So I gather that since the block containing resistors 2-5 is in...
  43. T

    Plot the graphs of power dissipated in pure resistor

    I am trying to plot the graphs of power dissipated in pure resistor , pure capacitor and pure inductor against time . My question is when i plot the voltage and current graph for pure resistor , i know they are in the same phase , but V0 is greater or Io is greater , i think Vo is greater...
  44. K

    Finding the current on each resistor

    Homework Statement [PLAIN]http://img297.imageshack.us/img297/7053/96217079.jpg given this circuit find the current on R1,R2 and R2Homework Equations I = V/RThe Attempt at a Solution i applied kirchhof's law and I have this: 36 - 5*I - I1*4 = 0 36 - 5*I + 20 - 2*I2 - 14 = 0 20 - 2*I2 - 14 +...
  45. M

    Current Through Resistor in Rectangular Loop

    Here is the problem and the equations I feel are relevant. The instructor was not clear on whether or not R2 was moving with velocity v, but I assume so because something must be moving (I think). Can somebody give me some instruction on where to go from what I have...
  46. T

    Magnitudes and Directions of Currents in Resistor

    Homework Statement please see attached picture. Homework Equations The Attempt at a Solution
  47. R

    Calculating Current in a Single-Loop Circuit with Resistor and Capacitor

    Homework Statement There is a Battery connected to a single loop circuit containing two resistors, R1 and R2, and one capacitor L. After a long time, the battery is removed, so there is a single loop circuit with just two resistors and a capacitor. What is the current going through R1...
  48. E

    Voltage controlled resistor circuit Help

    I have a unit that measures temp with a thermistor. I want to use it to measure voltage. I am trying to build a circuit to emulate a thermistor. Here are the parameters. 24v control = 37.8K. 1v control change = -1k so there is an inverse relation ship. Control voltage range = ideal is 6...
  49. S

    : Finding the Current and Power across each Resistor in a Complicated Network

    URGENT: Finding the Current and Power across each Resistor in a Complicated Network Homework Statement For the circuit below, a 12 V batter is connected across the points a and b. Determine the following: a) the equivalent resistance between points a and b b) the total current flowing...
  50. J

    Engineering Find the voltage across a resistor in a difficult circuit

    Homework Statement Find the voltage across R1 (see attached image). Note that all values are known. Homework Equations Voltager divider might be used. I hope KVL doesn't have to be used here. The Attempt at a Solution My problem is that I don't know if the current from I1 is...
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