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. J

    Calculating Equivalent Resistance of Resistor Network

    Homework Statement Show that the equivalent resistance is Req = 1/2 [(4RtRl + Rt^2)^(.5) + Rt] http://img74.imageshack.us/img74/5905/pingib2.png Homework Equations The Attempt at a Solution So far all I can get is Req = Rt + Rl Rt/(Rt+Rl) from the first three resistors starting from the...
  2. C

    Help With 15.15 & 15.16: A Capacitor + Resistor Circuit

    Hi. I've no idea how to answer the following questions. Could someone please help? I'd really appreciate it. 15.15 A capacitor is joined in series with a resistor, a low resistance microammeter, a switch and a 12 V battery. (a) When the switch is first closed, what is (i) the p.d...
  3. E

    Estimate Resistor Temperature Change with DC Voltage

    I am working on getting an MSHA approval for a device and I would like to estimate what the surface temperature of a resistor will be over time. Is there a way to calculate the surface temperature (temp change per unit time perhaps) of a known resistor if a simple DC voltage is applied...
  4. F

    Magnetic force with spring and resistor problem

    I am having a great deal of trouble solving the following problem. Can anyone help? A straight wire of mass 10.2 g and length 5.0 cm is suspended from two identical springs that, in turn, form a closed circuit (Fig. P19.66). The springs stretch a distance of 0.51 cm under the weight of the...
  5. N

    Choosing Resistor for LED Circuits

    I'm hoping this is the right forum for this question, I've never been to this part of PF before. I've taken up some interest in working with LED lights but I'm slightly confused with how to build the circuits for them. I'm told you need to put in a resistor to keep the LED safe from high...
  6. I

    Resistor - four terminal device

    I've read of resistors being referred to as four terminal devices, and capacitors being referred to as 3 terminal devices, can anyone explain this? or point me to a source that explains it, I can't find anything about it online.
  7. N

    Engineering Finding current in a resistor (in a big circuit)

    hi, can anyone help me with this problem? i need to try find the current in the 50ohm resistor marked with an 'x'. any help would be greatly appreciated!
  8. N

    Circuit, One resistor, two paths

    In a circuit where there is one resistor in one path and a separate path with no resistance, will all of the current go through the second path?
  9. D

    How to solve the infinete resistor network

    find resistance between A & B :bugeye: I'm sure it's not 1 ohm but i don't know how to solve http://www.pantip.com/cafe/wahkor/topic/X5389102/X5389102-1.jpg
  10. R

    Calculating an unknown resistor

    What do I have to do to calculate the value of the unknown resistor? The galvonometer reads 0 AMPS. I don't understand how the galvonometer changes according to where it's connected to the resistance wire. I thought amp meters read the same no matter where they're connected in the circuit. Just...
  11. V

    Current across resistor and inductor

    Homework Statement I have a resistor and an inductor in series. The current across each is the same, correct? I want to know if I can use Ohm's Law to solve for current across the inductor if I know the Voltage and inductive reactance. Basically, does I = V/X_{L} ? Homework Equations V...
  12. N

    Calculating Current in Circuits With o.3μF Capacitor and 40Ω Resistor

    A o.3micro farad capacitor is connected across a 15V, variable frequency ac power supply. Find the current in the circuit when the frequency is a) 100herts (b) 100kilohertz c) solve this question if thee 0.3 microfarad capacitor is replaced by a 40 ohm resistor. My solution I = wCV a)...
  13. M

    Analyzing Conditions for Current Flow Through Resistor R

    Homework Statement The drawing shows a wire loop near a current -carrying wire. Under what conditions would current flow through resistor R from Right to left? Homework Equations Lenz's law The Attempt at a Solution 4 answers a) when the current I is increasing b)when the...
  14. V

    Phasor circuit problem: 1 resistor, 1 capacitor, 1 inductor, 1 Voltage source

    Homework Statement What value of \omega will cause the forced response v_0 in the circuit below to be zero? http://img248.imageshack.us/img248/1854/problem934ao5.jpg Homework Equations Phasor eqs. The Attempt at a Solution...
  15. S

    Investigation on a Light Dependant Resistor

    Special lamps may be purchased to help plants grow indoors. These lamps produce light with wavelengths comparable to natural sunlight. A manufacturer wishes to check these lamps by measuring the out put of the lamp at different wavelengths. The above is the scenario given :smile: You are...
  16. C

    Cathy's Question: Motor on/off with LDR and Resistor?

    I've no idea how to start the following question so any help or guidance would be really appreciated. A potential divider circuit is set up with a LDR and a fixed resistor, R. The LDR has a resistance of 200 Ω when it is light and 2500 Ω when it is dark. A motor is set so that it comes on if...
  17. B

    Calculating the Current Through a 10-ohm Resistor

    Homework Statement A 10-ohm resistor has a constant current. If 1200 C of charge flow through it in 4 minutes what is the value of the current? A) 3.0 A B) 5.0 A C) 11 A D) 15 A E) 20 A The Attempt at a Solution I get B as an answer. I=(Q/t). I= 1200C/ (4 * 60) = 5.0 A The book...
  18. C

    Lenz's and Faraday's Law Induction. Help on resistor and switches

    Lenz's and Faraday's Law Induction. Help on resistor and switches! Homework Statement Find the direction of the current in the resistor shown below a) at the instant the switch is closed b) after the switch has been closed for several minutes and c) at the instant the switch is opened...
  19. J

    Zener diode-finding Resistor value

    Need some help finding the value of the input Resister... Design a 7.5V zener regulator circuit using a 7.5 zener specified at 12 mA. The zener has an incremental resistance of 30 ohms and knee current of .5 mA. The regulator operates from a 10 V supply and has a 1.2 k-ohm load. What is the...
  20. C

    Heating Water Using Circuit Resistor

    Homework Statement In a circuit a 20-ohm resistor sits inside 104 g of pure water that is surrounded by insulating Styrofoam, there are additional resistors in the circuit. If the water is initially at temperature 10.5 degrees celcius, how long will it take for its temperature to rise to...
  21. P

    How to calculate current of a resistor inside of another parallel resistor?

    How to calculate current of a resistor "inside" of another parallel resistor? The 1st image is how he drew it for us, no text.. I guess because it's quite complicated. He asks a bunch of questions, I've answered.. 1. Equivalent resistance of R3 and R4=5 ohms 2. combined resistance of R6 and...
  22. P

    2 series resistorss are in parallel with another resistor

    2 series resistors are in parallel with another resistor.. Homework Statement Resistors R1, R2, R3 have resistances of 15ohms, 9, 8.. R1 and R2 are in series and the combination is in parallel with R3 to form the load across a 12 volt battery. a)diagram b)total current c)Current across R3...
  23. D

    Solving a Diode Circuit: Output Voltage & Resistor R Values

    Homework Statement A scheme of a diode circuit is attached. The voltages at the inputs A and B are 5V. A. What is the output voltage (=voltage at the black node, Z)? B. What values of resistance would you recommend for the resistor R? 2. The attempt at a solution A. The diodes D1 and...
  24. D

    Diode OR Gate - the role of resistor

    Hi! What would happen if the resistor in the attached diode OR gate removed (connection with the ground would be preserved)?
  25. S

    Capacitor and resistor in a flowing liquid

    Homework Statement A parallel-plate capacitor with cross-sectional area S and plate separation d is put into a stream of conducting liquid with resistivity \rho. The liquid moves parallel to the plates with a constant velocity v, and the whole system is located in a uniform magnetic field of...
  26. D

    Finding the current across a resistor

    Homework Statement The currents are flowing in the direction indicated by the arrows. A negative current denotes flow opposite to the direction of the arrow. Asume the batteries have zero internal resistance. Find (part 1)the current through the 5.3 ohm resistor and the 3.1 V battery at the...
  27. D

    Find Current I1 in 7.5 Ω Resistor with Kirchhoff's Rule

    Homework Statement In the circuit below: (a) Find the current I1 that passes through the 7.5 Ω resistor. Homework Equations Kirchhoff's Rule--Loops The Attempt at a Solution This was a problem in my textbook. The answer is .65 A, but I don't understand how to get that. I tried...
  28. M

    Mass,Spring, Damper vs Capacitor, Indcutor, Resistor vs ? analogy

    From a mathematic, linear differential equation point of view, and energy storage point of view, the concepts I mentioned in the topics are the same (I remember this being a concept in modeling control systems.) My question is, what are the same basic elements in other topics: thermal...
  29. N

    Does the resistance of an LDR vary with frequency?

    Hi frnds Iam working on an investigatory project wherein iam studying the variation of resistance of an LDR with intensity of radiation and frequency. Regarding the frequency dependence iam having a doubt as the results tht I've got arent consistent. Could anyone guide me... whether...
  30. R

    Can Two 15 Ohm 1/2 Watt Resistors Be Used for a 1.8 Watt Requirement?

    hello, I am new here.. so please excuse my..um. n00bishness im sorry if this under the wrong area, i doint know which area of physics it might be under, i just remember reading about resistors back in HS physics...which was years ago.. I'm currently building a shed lighting system through the...
  31. G

    Maximum current IN the resistor

    Here's what I know: A 1.89 nF capacitor with an initial charge of 5.26 mC is discharged through a 1.34 kW resistor. I'm supposed to find the maximum current in the resistor. I know the maximum current through the resistor is -2.077 A from the equation I(t) = -(Q/RC)*e^(-t/RC) and I know...
  32. T

    Equivalent 1000Ω Resistor Uncertainty

    my question is that i have two resistors that are combined to form an equivalent resistance of 1000 ohms. Now there are two common resistors rated at 500 plus/minus 50 ohms and two others rated at 2000 ohms plus/minus 5%. I need to know what combo (series or parallel) would provide the smaller...
  33. L

    Resistor Network: Find the Equivalent Resistance Across AB

    A resistor network is built up indefinitely as shown in the figure. The equivalent resistance across AB is A. 1 ohm B. 1.24 ohm C. 2 ohm D. unable to be determined. -> I don't know where to start with. Can anyone give me some hints?
  34. N

    How Do You Calculate Current Amplitude in a Parallel RC Circuit?

    A resistor with a resistance of 500 ohms and a capacitor with with a capacitance of 2 x 10^-6 f are connected in parrallel to an ac generator that supplies an rms voltage of 260 v at an angular frequency of 377 rad /s find the current amplitude in the resistor (Ir)peak. I know I have to...
  35. T

    Solving the Physics Riddle: A Current Across a Single Resistor

    Today in physics lecture our physics teacher left us with a riddle. If you had an infinite grid of resistors say with 1 ohm of resistance set up between every node of the grid and then you connected a battery that supplies a current of one amp through across a single resistor, what would be...
  36. P

    Solving a Differential Equation for Parallel Circuit with Capacitor, Resistor, and Inductor

    I have a circuit with a capacitor, resistor, and inductor all in parallel with each other. I have to write the differential equation governing the voltage. However, when I attempt to do that [using Kirchoff's Voltage Rule] I will end up with: Vc + Vl = 0 and Vl + Vr = 0 However, this implies...
  37. V

    Thevenin's Theorem - Dependent Source + Resistor

    Hey, I'm having a bit of difficulty with this one. I spoke to my professor specifically about this problem, he worked through it, I understood him, and I worked through it later in the day. I still get it, I worked through it, and there's step at the end that we both did differently. It seems...
  38. J

    Need help solving resistor network problems

    this isn't so much of a homework question . I am having trouble with identifying and calcultaing effective resistence for parallel or series connected resistors particularly ones that are very complex to even understand what's going on ... I did look through various websites and books looking...
  39. J

    Surface Mount Resistor Tolerance

    Hello, Is there a way to determine the tolerance of a surface mount resistor by its markings or coloration?
  40. L

    Which resistor gets most power in both series and parallel?

    three resistors that have values of 5,2,1 ohms, are connected in series and parallel to a battery, which resistor gets most power in both series and parallel?
  41. A

    Resistor Change from Aorta to Capillaries

    The aorta branches into up to 30-40 billion capillary vessels, 8-10 billion of which are used effectively. As a consequence the cross-sectional area increases by a factor of 800. If we start from the assumption that there are 9 billion capillary vessels (all of which are equally thick) – how...
  42. M

    Finding Frequency of 20mH Inductor & 30 Ohm Resistor in Parallel

    im given a a 20-mH inductor and a 30 ohm resistor in parallel. Z_in is 25 degrees. and I am asked to find the frequency omega in rad/s here's what i try to do: 25=(jw.02*30)/(jw.02+30), and solve for w, but i don't get the right answer. what is it that I am doing wrong?
  43. M

    Resistor Wattage: Higher or Lower for Low Resistance & Cooler?

    I am looking for a low resistance resistor to put in my circuit to lower the current slightly. My circuit is/will be running off a 12 power supply and normally will draw somewhere between 11 and 13 amps under normal operation. I would like to add in an additional maybe .5 to 1 ohm resistor so...
  44. G

    Resistor connected in series with a capacitor?

    Pls help.. If i have a capacitor of capacitance 3uF connected in series with a resistor, what will the potential difference across the 1ohm resistor when the EMF is 6V? Is the answer a zero? If yes, why? is it becoz the capacitor itself have make the circuit a open circuit such that no...
  45. C

    Calculate Current in a 50 Ohm Resistor from Half Wave Rectified Voltage

    im stuck on this question and was wondering if anyone could help point me in the right direction: a half wave rectified voltage is described by: v(t)=100.sinX (that X is mean to be theta) when applied to a 50 ohm resistor find the average and rms values of the current. thanks an help is...
  46. C

    Common emitter ampl. with emitter resistor degen.

    I would like to find the transconductance of such circuit. I am choosing to ignore r_0 for the time being and going with the definition G_m = \frac {i_0}{v_i} \bigg |_{v_i = 0}, What I did first was notice that i_0= - g_m v_\pi[/itex] v_i appears as the top node voltage at r_\pi w.r.t to...
  47. Cyrus

    Find current for circuit with capacitor, resistor, capacitor in series

    I have to solve this problem for a circuit. Its a capacitor, a resistor and another capacitor all in series. Both capacitances are the same, 1uF, and the resistor is 100k-Ohm. I have to find the current function of time. What I did was use KVL to get: - \frac{1}{c_1} \int i(t)dt...
  48. Cyrus

    Circuit Analysis: Voltage Across Resistor vs. Time

    Sorry, no picture my bad. Here is the circuit, everything is in PARALLEL, First its a 1mA source, then its a switch, then its a resistor of 10k-ohm then its a capacitor 1uF. Sorta like below: ---------------------------------- | ...| .... |.... | O...Switch ... R ... C |....|...
  49. T

    RMS Current in Circuit with Capacitor, Inductor, Resistor, AC Source

    Four circuit elements—a capacitor, an inductor, a resistor, and an AC source—are connected together in various ways. First the capacitor is connected to the source, and the rms current is found to be 25.1 mA. The capacitor is disconnected and discharged, and then connected in series with the...
  50. denian

    What are the closest standard resistor values to 175kOhm?

    if not, what resistance is the closest to 175kohm? tqvm.
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