What is Ohm: Definition and 72 Discussions

The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Ohm. Various empirically derived standard units for electrical resistance were developed in connection with early telegraphy practice, and the British Association for the Advancement of Science proposed a unit derived from existing units of mass, length and time, and of a convenient scale for practical work as early as 1861. As of 2020, the definition of the ohm is expressed in terms of the quantum Hall effect.

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  1. .Scott

    Is this really a 75 Ohm cable?

    There have been a few times in my career as a SW engineer when I have gone to the EE's on the project and they have been unable to answer my EE question. My thought is that if I post these problems on this message board, they might make it into the EE curriculum much to the advantage of newly...
  2. P

    Can I replace a 4 ohm speaker with a 4 ohm power resistor?

    Also would a passive filter add much resistance to the circuit and rob the speaker of power? Here is the 2 way lowpass filter I was thinking of. I don't need 2 of these obviously but they seem to come as a pair. https://www.amazon.com.au/dp/B07R613YSK/
  3. C

    Why a 20 Ohm lightbulb won't light up in a closed circuit?

    When using the voltmeter and ammeter to investigate the circuit, it was found that the batter had a current of 0.67 A, the two 30 Ω bulbs had a current of 0.17 A, and the two 10 Ω bulbs had a current of 0.50 A. In terms of voltage, each bulb had a voltage of 5 V. When the switch was closed, the...
  4. D

    Increasing the 50 Ohm bandwidth of an impedance-matched system

    Hello, Some trouble came up today with designing a 50 ohm system for a wireless powering project. I'd like to increase the frequency range for which my system impedance is 50 ohms in order to reduce power losses due to mismatch. I've simulated two RLC circuits in OrCAD SPICE to demonstrate my...
  5. P

    A Understanding Ohm and Hall Diffusion in Cosmic Rays

    Summary: I know that the diffusion of charged particles in a magnetic field is described as a diffusion tensor with 3 components: Diff parallel to the field, perpendicular and anti-symmetric diffusion. Is this last one that I do not understand. Dear community, I am PhD candidate in...
  6. Z

    Engineering Amplifier circuit driving an 8 Ohm speaker

    Homework Statement Hi all. I need a bit help with the following. Estimate the power developed in the 8 Ω speaker of the circuit of FIGURE 2 for a 1 kHz sinusoidal input signal of 100 mV peak. All capacitors may be assumed to act as a short circuit at the frequency of operation. Compare your...
  7. Wrichik Basu

    What is the use of 0 Ohm resistors?

    Today, I found that there exists something like a 0 ohm resistor: https://www.electroncomponents.com/0-e-ohm-resistor-resistance-zero?filter_name=0%20ohm%20resistor Don't look at the image in the page I can simply connect two points in a circuit with a good quality copper wire, thereby...
  8. F

    Ohm reading when there is a short in a condenser motor

    Preface to thread: The multimeter is set to read resistance in all the scenarios I ask about in this message. The word "COMP" in the ladder diagram stands for compressor motor. The three letters underneath the capacitor are DRC, which stands for Dual Run Capacitor...
  9. Helmholtzerton

    50 Ohm to 75 Ohm to 50 Ohm line?

    I'm trying to understand how I can mathematically describe a particular situation in order to calculate what I should expect to read on an oscilloscope. Let's say I have a signal generator that is generating a 1MHz sinusoidal signal 1Vpp. The source impedance of the signal generator is 50ohm...
  10. A

    Question about multimeter continuity

    Hi guys , i am working in the automotive industry today i encountered a weird electrical issue and i am sure you guys have an explanation , i was using my multimeter to check continuity between different stuff , by mistake i put the leads on the car battery terminals i found the multimeter...
  11. H

    Can you help me find the current through the 15 Ohm resistor branch?

    Homework Statement Homework Equations I = VR Series = current the same, voltage different Parallel = current different, voltage the sameThe Attempt at a Solution Is the 1 ohm and 15 ohm parallel? I'm still learning to differentiate it. If yes, then R = 15/16 ohm Is the R series to 5ohm? If...
  12. N

    B Solving a Circuit: Neglecting the 1 Ohm Resistor

    I want to know why in this problem in the solution, he disregarded the 1 ohm resistor and found the equivalent resistance of 6 and 3 ohms right away. https://imgur.com/a/efG11
  13. Plat

    Mains transformer with 1.4 ohm primary winding?

    I don't understand how this is possible. This is a rather large transformer in a stereo system amplifier. The transformer is a simple step-down with 120V mains primary to a center-tapped secondary providing both 38V and 76V. According to ohm's law, at 120V this thing should draw about 85 amps...
  14. AAO

    Which RTD is better for noise-reduction: 100 ohm or 1k ohm?

    Hi all, We are planning to use RTD (Resistance temperature detectors) for our system which basically are temperature sensors that contain a resistor that changes resistance value as its temperature changes. The RTD can come in two nominal values: either 100 ohm or 1k ohm. Knowing that the RTD...
  15. E

    Why the rule of thumb: 1Mega ohm max when doing PCBs?

    My curiosity was peaked when looking at this application circuit from linear: http://cds.linear.com/image/Fig2_-_Wireless_Current_Sense_Circuit_Floats_with_Sense_Resistor.png They put two 2M resistors in series instead of one 4M resistor. I've never really used anything bigger than 470K so I...
  16. A

    How to make total resistance of 1 ohm?

    Homework Statement We have 1Ω, 2Ω, 2Ω, 4Ω, 5Ω and 6Ω resistors. We have to make a circuit with all of them and total resistance must be 1 ohm. Homework Equations Parallel: 1/R1+1/R2=1/R In series: R1+R2=R The Attempt at a Solution I have only made a circuit from 4 resistors: 1 ohm and 2 ohms...
  17. J

    What is current across 5 ohm resistor

    Homework Statement Find the current across 5 ohm resistor Homework Equations Superposition theorem. Other voltage sources become short circuit and current sources become open circuit. Ohm's law. I = V / R The Attempt at a Solution Using superposition theorem, we get: When only left side 10...
  18. B

    Finding current in the 25 ohm resistor

    Homework Statement The problem is to find the current in the 25 ohm resistor (left side) http://imgur.com/a/luKCW [Image inserted by moderator] Homework Equations KCL KVL ohms law (v=IR) The Attempt at a Solution My attempt at the solution was to add both power sources together (-5v(-5v...
  19. Abysmaltan

    Solving Circuit with Ideal Ammeter: 4.0 Ohm Resistance

    Homework Statement A circuit is setup with an ideal ammeter connected across the 4.0 ohm. What will the reading of the ammeter be? 2. The attempt at a solution I am not sure whether the question is testing my understanding on how an ammeter should be connected in a circuit or about how to...
  20. P

    Can Henry be converted to Ohm?

    Homework Statement I came across a question in my homework sheet where it give the unit of "L" in ohm when it supposed to be "Henry" (right?). So I just wondering, can ohm be converted into Henry? Homework EquationsThe Attempt at a Solution
  21. G

    USB power bank: How can both voltage and current be given

    Hi. I'm still confused about basic electricity. I have a USB power bank with two 1 A and one 2.1 A outputs. They all are specified with 5 V (all numbers from the manual, not measured myself). I just can't bring this into agreement with Ohm's law U=RI. Shouldn't the resistance R only depend on...
  22. N

    How Does Ohm's Law Apply to Parallel Circuits?

    *U=voltage Homework Equations U=IR (V=IR) The Attempt at a Solution 200mA=0,2A --> 0,2*50=10V...? So because it's parallel the source should be 10V too right?
  23. terryds

    Circuit problem -- What voltage value makes the energy absorbed by the 6 ohm resistor....

    Homework Statement A circuit is arranged like above. To make the energy absorbed by the 6 ohm resistor every second is 1.5 J, voltage X should be ... Volt Homework Equations V = IRThe Attempt at a Solution [/B] I really have no idea. I just know that it's kinda like wheatstone bridge and...
  24. H

    Do 40 Watt 1 Ohm resistors exist

    My local hobby store says no. I want to draw a full 40 Amps from my power supply to play with a few formulas that give the magnetic field strength as a function of distance and current from a wire. The wire will be car battery cables. I have a calibrated Gauss meter for field measurements...
  25. T

    Impedance matching between two 50 ohm cables through a joint

    Hi, I'm in a bind trying to determine how to handle impedance matching through a joint of copper wire sandwiched between two 50-ohm coaxial cables (the joint is an interface between atmosphere and a UHV system). There is a signal pulse with a rise time of 2 ns coming through one of the coaxial...
  26. UMath1

    Voltage in Circuits: Explaining Voltage Drops & Flow

    I feel that I don't understand how voltage works in a circuit. I understand voltage to be electric potential energy per unit charge (kq/r). In the case of a circuit, electrons flow from low potential to high potential. But I don't understand how resistors cause a voltage drop. Isn't voltage...
  27. T

    Engineering Circuit (equivalent resistance)

    Homework Statement Find the equivalent resistance Homework Equations Req(series) = R1 + R2... Req(parallel)=(1/R1+1/R2...)^-1 The Attempt at a Solution I'm having problems understanding how to simplify this circuit. There should be parallel and series "loops" to simplify but I'm having...
  28. MushroomLT

    Can a different Ohm rating resistor burn a pc motherboard?

    Hello, my motherboard recently has stopped working, so I returned it to warrany, they fixed it, but after a few months the board broke again, but unfortunatly the warranty has ran out, so I'm attempting to fix it myself in the freetime :D So I have found a resistor on the motherboard, that looks...
  29. SmokeyMTNJim

    Resistance and DC circuit question

    Here is the problem: I have already lost the ability to get the correct answer for AI Homework Statement (a) What is the maximum potential difference that can be applied to the terminals a and b? 33.541 Which resistor will have the largest current? V (b) For the voltage determined in part...
  30. Heros

    Uncovering the Mystery of Non-Linear Torque in Muscle-Powered Energy Conversion

    Hi, i didnt know where to put this question cos its kind of multitopic, here is why... I am working on a better way to take mechanical energy from muscles, i made a teste bench for pedalling in very different ways, including traditional(circular) pedalling, the thing is. I am measuring the power...
  31. davenn

    What is the relationship between resistivity and the Ohm meter?

    I just need a clarification, I have been through a dozen www sites and cannot find an answer they show how resistivity is worked out eg ... the Ohm meter is usually shown with a "dot" between Ohm and metre Is this the same as Ohm times metre ? or Ohms per metre or something else? I would...
  32. A

    When 1 mega Ohm resistors are used?

    When and "for what purpose"/why are 1 mega ohm (1 MΩ) resistors used in filters, such as high pass filters? Is it with regards to electrostatic discharge or impedance matching? What difference does it make, if I only use a 10 K ohm resistor, when the high pass frequency will be the same (by...
  33. marellasunny

    Can I use a ordinary 1K ohm potentiometer to convert 12V to 5V?

    I have a 1K ohm potentiometer.(datasheet is attached below). My aim is to convert 12V to 5V,which I would then apply to power the Arduino microcontroller. I'm not quite sure if I CAN use the potentiometer I have ie T93 YA 1K 1035 to do this conversion. The datasheet says that the maximum...
  34. Entanglement

    The original definitions of Ohm, ampere, volt and coulomb

    What's the original definition of Ohm, ampere, volt and coulomb, And which unit was defined according to the other ??!
  35. J

    How many electrons does one Ohm prevent/resist?

    Hello All! I am having a rather difficult time locating the answer that I am seeking. What I am trying to determine is a little more understanding about resistance. I know that 1 Amp is coulombs per second, and that is 6.241×1018 electrons. I know that 1Ω is 1 Amp across 1 Volt. However what I...
  36. B

    Find the oc voltage and the voltage across the 5 ohm load

    Homework Statement https://dl.dropbox.com/u/3405118/24-02-2013%2018-46-54.png Find (a) the open-circuit voltage VL , and (b) the voltage across the 5 ohm load, by the following methods. Method 1: Direct approach. First find the open circuit voltage by simple ‘potential divider’ approach (but...
  37. J

    Find the current through the 100 Ohm resistor:

    Homework Statement Find the current through the 100 Ohm resistor: http://imgur.com/sohdpyE The Attempt at a Solution So I was able to simplify the 100 and 500 resistors, as well as the 20, 20 and 10 series resistors, but I can't seem to discern at all whether any of the remaining ones...
  38. Drakkith

    Voltage Drop in a Series Circuit with 100V & 2 50 Ohm Resistors

    Ok, let's say you have a 100v voltage supply and two 50 Ohm resistors in a series circuit. The total resistance is 100 Ohms, leading to a current of 1 amp. Now my question is, what exactly is voltage drop? I know the voltage drop across each resistor is 50 volts. If we were to look at one of...
  39. B

    Can I hook a 50 Ohm Variable Attenuator To This Circuit?

    The is the Output circuit of a microphone I'm using to look at photoacoustic signal, is just an Op-Amp, connected to a high pass filter which is using a 30 Kohm resistor. Sadly, the signal the microphone gives is too strong for the lock-in I'm using to read the signal, and overloads it. I want...
  40. H

    Engineering Design a circuit w/1 Ohm impedance

    Homework Statement Design a suitable combination of resistors, capacitors, and/or inductors which has an equivalent impedance at ω=100 rad/s of 1Ω using at least one inductor. Homework Equations Zeq=ZR+ZL+ZC ZR=R ZL=jωL ZC=-j/ωC The Attempt at a Solution I really am not sure how to start. I...
  41. A

    Solving 2 Questions on Circuit Analysis: PD Across 3 Ohm & EMF of Batteries

    Homework Statement I have two questions. Both questions are in the picture below. Dont mind my workings lol http://img163.imageshack.us/img163/5680/scanpic0001qe.jpg Ans to the 1st qn: C The potential difference across the 3ohm resistor is zero. Thus, it can be considered that the 4ohm and...
  42. K

    How Do You Calculate Current in a 10 Ohm Resistor Using Kirchhoff's Loop Rule?

    Homework Statement Find the current in the 10.0 ohm resistor in the drawing (V1 = 24.0 V and R1 = 15.0 Ohm) Diagram: Homework Equations Kirchoffs loop ruleThe Attempt at a Solution well do i have to solve for both parts of the circuit if i just want to find the current at the 10.0 ohm...
  43. T

    Use resistor simplification to find current across the 10 ohm resistor

    Homework Statement Use resistor simplification to find current across the 10ohm resistor Homework Equations V=ir p=vi The Attempt at a Solution Any help you can give me is much appreciated. When I did it i got down to a parallel circuit with a 30ohm and a 100ohm but didnt get a...
  44. C

    Using a Matching Transformer for 50 Ohm to 75 Ohm Coax

    hello, good afternoon. I'm a little bit confused about the use of matching transformer. I made a 50 ohm tv antenna, and i connected it to a 50 ohm coaxial line. However, I've found out that for tv applications, 75 ohm coax should be used. my question is, if i will replace my 50 ohm coax, can i...
  45. A

    What ohm resistor should I use for my transformer's extra capacity?

    This will (maybe) be an easy question to answer. Here is my situation: I have a 12v 200mA capacity transformer (wall wart) that I am using to power up a relay which takes about 5mA and has an input voltage range of 5-24v. Basically I need to burn off the other 185mA or so of the transformer's...
  46. S

    500 ohm resister fed from 120 VP-Pac source

    Homework Statement a 500 ohm resister is fed by 120 Volt P-Peak ac source;How much heat does the resister dissipate if the signal is a sine wave or a square wave? Homework Equations The Attempt at a Solution
  47. Femme_physics

    Understanding the Ohm: Definition, Explanation, and Examples

    I'm not sure I understand this definition, it's written in a rather confusing manner...instead of saying how much ampere is being stopped from flowing, it tells us how much current is being produced! That's a little confusing...I thought the definition for the resistance SI unit would be how...
  48. W

    Ohm's Law in Transformers: Voltage vs. Current

    In transformer when voltage increases on secondry coil then current decreases but i am confuse here that how ohm law is obeyed here. as V is d.proportiona to Current. please advise...
  49. K

    Finding EMF Required for a 22A, 5 Ohm Heater Coil

    Homework Statement A current of 22 amperes flows in a heater coil whose resistance is 5 ohms. What E M F in volts is required? Homework Equations The Attempt at a Solution Not quite sure where to begin. I'm thinking the internal resistance, R, is inherent w/the circuit so EMF...