What is Ohms: Definition and 68 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. A

    Why does the top surface of a Silicon Die measure close to 0 ohms?

    I have gotten access to a large bare silicon die (almost 1" across, 14nm process) that my company gets from a fab. I've been monkeying around with an ohmmeter placed at the top of the die, with the test leads placed at various points around the die, and I almost always measure the same value...
  2. S

    Engineering Find Current Through 40 Ohms Resistor Using Thevenin

    Find the current through the 40ohms resistor using the Thevenin? I have calculated the Zth = 10 ohms. And I couldn't find the Vth.
  3. Boltzman Oscillation

    Must a load consume the entire available current or only what it needs

    So if I have a source of 5V and 20 amp then the maximum power I can get from the source will be: $$ P_{max} = 5*20 = 100W$$ but my load can only take in 5 watts, it will blow up. But, does this have to happen or does my load only take what current it needs? My guess is that the load takes in...
  4. Boltzman Oscillation

    Understanding Basic Electronics: A 9V Battery & Two 9V Bulbs

    Homework Statement:: How can I determine whether my basic circuit will work? A battery and two light sources. Homework Equations:: conceptual question, use basic ohms law, current law, voltage law, etc. This is not a homework question, i am just trying to understand electronics better. I am...
  5. K

    Electric Circuts (Voltage, Ohms, Amps)

    I made a chart and this is my attempt. I am not sure that I am doing the calculations right thou
  6. ry12

    Understanding Power Equations: How Do You Solve for V2 and R in Ohm's Law?

    Hello everyone new here :) I've recently enrolled myself in a computer technician course and I've encountered a few (basic) electrical sums. I have absolutely no electrical background, and the course mentioned no requirement of such, but I'm already being presented with work I have no idea of...
  7. B

    Confused with the relationship between Volts, Current, and Power

    Homework Statement For an engineering assessment (first year with no electrical background), we are using a solar panel to power an element for a distillation system. we have calculated our heat energy output requirement that we need from our heating element as being 800 J/s. For simplicity we...
  8. J

    Coil resistance increases from 54 ohms to 8k at 220kHz, why?

    edit: The key thing I am after is why the ferrite might be responsible for the increase in resistance I measure on the coil. Hello, i have a coil designed to be 2.2mH and54 ohms. When an MN60 ferrite (T-ish core) is used with it, the inductance rises to 6.1mH as expected, and the resistance...
  9. A

    Circuit Problem -- Combining 4 resistors to make 95 Ohms

    Homework Statement 1. Use resistors of 30 ohms, 40 ohms, 50 ohms, and 50 ohms to create a circuit with a total resistance of 95 ohms. 2. Find the amount of current going through two of these resistors if the circuit is attached to a source of 12 v. 3. What would be the voltage drops for the...
  10. M

    Lab: Plot graph of resistance, R (in Ohms) versus 1/d^2

    Homework Statement We were given five samples of nichrome wire, each with a different diameter but the same length. A micrometer was used to measure the diameters. We then measured and recorded the electrical resistance, R in Ohms of each nichrome sample with a DMM. I will try to summarize all...
  11. Glurth

    Odd troubleshooting results: disobeys ohms law

    I have a DC powered pump, that has suddenly stopped working. During troubleshooting I came up with the following results, that I just cannot reconcile: Input wires, not connected to pump: 12v Input wires connected to pump: 0v Sounds like a short in the pump right? However, connecting the...
  12. N

    How to convert Ohms to luminosity?

    So, I recently joined a stargazing club, and for our summer activity, we're supposed to use a telescope, a photoresistor, and a multimeter to measure the luminosity of the moon. I know that luminosity can be calculated with the equation, L = σ AT 4, and that brightness can be measured with the...
  13. B

    Graphical or calculation solution. Which is better? Ohms law

    Homework Statement A student is calculating the resistance of a piece of fuse wire. He takes 5 readings on the voltmeter and ammeter for different settings of a variable resistor. He decides that instead of measuring the gradient of the graph to calculate the resistance, it would be okay to use...
  14. B

    Book wrong? Ohms law, Graph, wire, slope change question

    Homework Statement Hello. The resistance of a wire increases when the temperature increases. How would this cause the shape of the graph to change? Explain why. The graph shown is a straight line graph with the line traveling at 45 degrees path. The x-axis is VOLTS. The y-axis is CURRENT...
  15. P

    How does corrosion affect the resistivity of copper wire?

    I'm not sure if corrosion does have a significant effect on copper in general but if it does, how and why does it happen, and the process of it happening and its effect on the overall resistivity? This is for a physics assignment...Please help if you can. Thank you
  16. U

    MHB Wire Length w/ 0.068 Ohms & 2.8mm Diameter: ~11.56 ft

    The electrical resistance of a wire varies directly with the length of the wire and inversely with the square of the diameter of the wire. If a wire 50 feet long and 2 millimeters in diameter has a resistance of 0.265 ohms, find the length of a wire of the same material whose resistance is 0.068...
  17. 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...
  18. True Rock

    Why is the terminology in electrical engineering so redundant and confusing?

    I've been trying to brush up on my electrical engineering skills and have been working on the circular and redundant terminology of amps, volt, ohms and watts. It seems to me it all comes down to a quantity of electrons (i.e. coulombs). And, for various reasons perhaps the number of electrons...
  19. I

    OLED Watt, Ohms, and Volt Project

    Hi, I am in fact quite new to these forums but have been lurking for a while. I am trying to design a OLED reader that will display the watts, ohms, and volts after being read from a circuit. Almost exactly like this: Any ideas on where to start? I am not necessarily a novice when it comes to...
  20. B

    Designing a display for Watts, Volts and Ohms.

    I am working on a small project and having those values shown in real time on the device will be helpful. I don't have much room as it is. I currently have one of those little 1s-6s volt meters used by RC hobbyist and use my multimeter to check resistance. My goal is to have something around...
  21. O

    Question about Finding unknown resistance by Ohms and Kirchoff's Laws

    Homework Statement Using Ohm's and Kirchoff's Rules find the unknown resistance Rx Homework Equations V = IR Sum of currents at a node is zero Sum of voltages around a loop is zero The Attempt at a Solution For the 2 ohm resistor I found the voltage to be 4V by the formula...
  22. I

    Nodal and Mesh Analysis vs Simple Ohms law?

    At high school we were taught basic circuit formulas such as V=IR, P=IV etc but now I am studying circuits in Engineering (at university) we have been introduced to the techniques of nodal and mesh analysis. My question is, when and why do we use these techniques rather than the...
  23. S

    Heating water with amps ohms and time

    so if i have 89.6g water at 304K and a constant p=1.00bar and i heat it by running 1.75A through 24.7 for 105 seconds what will the final temp be? im thinking i can take q=mC(Tf-Ti) and q=IT and I=R/V to say that Tf= (Rt/vCm)+Ti i can't rember that much about physics and this stuff...
  24. B

    Connection between coloumbs , ohms and magnetic flux density

    what is the connection between coloumbs , ohms and flux !
  25. R

    Solving Umax with Pmax and Ohms

    Brief personal intro, I have last time studied physics about 12 years ago. I am now starting in 2 weeks time in a university and there is mandatory physics course so I am trying to relearn and learn as much as I can before that time. For that reason I am trying to solve textbook tasks...
  26. R

    Omggg Determining voltage between point a and b given R = 40 ohms

    Omggg :( Determining voltage between point a and b given R = 40 ohms This is what I did for part A:1) ΔVrms = Vmax(1/√2) ΔVrms = (145)(0.707) ΔVrms= 102.53 2) Ztotal = √[R² + (XL - XC)²] XL = 2πfL XL = 2π(40)(185 x 10^-3) XL = 46.49 XC = 1/2πfC XC = 1/[2π(40)(65 x 10^-6) XC =...
  27. B

    Engineering Electrical circuit porblem using ohms law

    Homework Statement Using all the following resistors : 2 x 12 ohms , 2 x 24 ohms , and 2 x 36 ohms. create a circuit where the total resistance will be 4 ohms. The problem states that I have to use ALL of the resistors..making it so complicated Homework Equations 1/Req = 1/R1 + 1/R2...
  28. J

    Ohms Law Load Amp Resistance Change

    I have a solar cell that is rated 3.6 amps .5 volts 1.8 watts when you take a ammeter it does put out 3.6 amps, but this is basically a dead short reading. What I want to know is these cells put out .5 volts using ohms law how much resistance is needed to have a voltage output of .3 volts so you...
  29. mrspeedybob

    Question about ohms law and non-ohmic behavior.

    I recently learned that ohms law is not always obeyed. I found this surprising because I thought ohms were defined in terms of volt and amperes by the equation R=V/I. I did a little googling and found the following definition... This clarified things a little in that the definition of an ohm...
  30. G

    Ohms law implies specific condition for the charge density

    We have all seen Ohms law, J=σE. This approximations makes sense in simple electric fields in which the charges are accelerated in parallel. However as I will demonstrate, this implies a few conditions on the charge density (ρ) associated with the current density (J). Now, from the continuity...
  31. Z

    Ohms law for concentric spherical shells

    Look at the attached problem with solutions. I don't understand what the author means in c) when he says that succesive shells contribute less and less because the cross sectional area grows proportional to r2. The flux through a closed surface is always the same (Gauss' law). Rather the reason...
  32. T

    Resistors, potential dividers and ohms law

    Here is my question: When I look a p.d divider circuit I get slightly confused, because the way I was reading the explanation it says: that when the a thermistors has 0 resistance it has 0V across, so when the resistance increase the voltage increases and the will turn on the base emitter to...
  33. J

    Unlimited resistors to build a 5 watt circuit with resistance of 10 ohms.

    Okay well my issue is from a basic problem. The problem is you are given an unlimited number of 10 Ohm resistors. They can only handle 1 watt of dissipation and you need to create a circuit that has a total resistance of 10 Ohms, and has a power dissipation of 5 Watts. They are actually looking...
  34. C

    Engineering Need Help With Series-Parallel Ohms Law Circuit Math Problem

    Homework Statement Total Volts: 10 Resistor 1 - R1: 1K Resistor 2 - R2: 4K Resistor 3 - R3: 4K Photo That I Made Of The Series-Parallel Circuit: http://imageshack.us/photo/my-images/266/circuitn.png/ Homework Equations...
  35. R

    Multimeter Ohms exponential scale; formula?

    Homework Statement Hi, I'm asking the usual "what formula gives me these results" question, but with a twist; I'm attempting to make a "virtual" analogue multimeter that replicates a physical piece of equipment, for training purposes. The idea is that a random MegaOhm value will be generated...
  36. S

    Ohms Law and Its Practical Limits: Investigating a 10um Steel Wire

    Does Ohms Law have practical limits? For example:A piece of steel wire of length of length 10um and of CSA 20E-10. Can we calculate the resistance of such a tiny piece of wire (resistor) in the usual way? thanks
  37. F

    Understanding biasing and ohms law

    Hello, I am trying to get my head around biasing. I do understand the principles. In the attached circuit the Collector current is 2.5mA and the collector resistor is 1K. Therefore my circuit here is biased at 2.5V. The power supply is 5V. So that would give a 2.5V drop over the collector...
  38. B

    Finding Constant for Ohm's Law: Correlation or OHMs Constant?

    1. Write the equation for each run in the form (potential=constant x current) {the form has two numerical list to work with} 2. How do I find the constant from these 2 lists? Is it the correlation that the question is looking for? or, Is it OHMs constant, that the question is talking about??
  39. H

    Relativistic Ohms Law: Modeling 1D Hot Electron Beam in Plasma

    A colleague and I are looking at modelling a hot electron beam hitting a initially charge neutral plasma. Initially we're looking at the 1D problem, the equations we're using are: \begin{array}{rcl} \gamma^{3}(v/c)\left(\frac{\partial v}{\partial t}+v\frac{\partial v}{\partial x}\right) & = &...
  40. A

    Help With Circuits Regarding Ohms

    Hello, I feel like an idiot because I can't answer this myself (I forgot my high school physics). I have a stereo amp head that has two speaker outputs at 75w each. Each of these outputs has a resistance of 8 ohms each. My cab, however, is mono, and only has 1 speaker input. The cab I own is...
  41. S

    Understanding Ohms: A Beginner's Guide

    Homework Statement This is not exactly a homework problem, but it's one that marks me as a beginner: is there an intuitive physical understanding, using dimensional analysis, of the unit combination making up the "ohm"? I don't mean a physical understanding of resistance--that's not a...
  42. D

    Ohms law question. Series and Parallel in same circuit.

    Homework Statement See picture. Homework Equations Ohms Law-V=IR The Attempt at a Solution i do not know what to do once i find Rt (8.714...) because there is a parallel and a series in this circuit...
  43. C

    How does adding length to an extension cord affect Ohms Law?

    I've never really understood the relationship between voltage, current, and resistance. The more I read about them, the less comfortable I feel discussing them. V=IR...mathematically, it doesn't get any simpler than Ohms Law, yet when I try to predict the behavior of its variables in real world...
  44. E

    Thermistor Temperature- Ohms Law?

    Thermistor Temperature- Ohms Law?? Hi All! I am trying to convert a current of 795mA to a temperature in degrees celcius but I don't understand how to do it. I realize that Ohms law of V= A/ R is involved somehow but that's the extent of my knowledge. PLEASE HELP! I have also been...
  45. F

    Why use 75 ohms on TV cables

    we learned it could be a trade off between loss and flexibility. Because if it was around 50 ohms or so it would be too thick of a wire. and the we learned the minimum loss is around about 77 ohms. What do you guys think.
  46. T

    A bit of help with KCL and ohms law please

    i have attached a picture showing the problem; just wanting to know if my working out and reasoning is correct please. http://img29.imageshack.us/img29/5412/questionsq.jpg The Attempt at a Solution i have used KCL to answer (a) and (b) and have answers 0.6 and 1 respectively. for (c) and (d)...
  47. B

    Bus Frequencies and Ohms Law

    What does increasing the frequency of a computers main bus [the bus that connects the CPU to the chipset] imply about the voltage ["information"] traveling on a bus? (what IS the frequency of a bus effectively measuring, data units per second?) The way i see it (please correct me if I'm...
  48. D

    Doubling Resistance of 1 Mile Copper Wire - 68 ohms

    Homework Statement A 1 mile long copper wire has a resistance of 68 ohms. What will be its new resistance when doubling it over and using it as "one" wire Homework Equations? R=V/current The Attempt at a Solution unable to attempt, I know that when it is cut in half R=34 ohms
  49. Q

    Why does OHMs law not work on AC circuits?

    can someone please explain to me physically how is it that when i have an AC source and i measure Voltage on a resistor its the same with and without the resistor and when i have a DC source and i measure Voltage again on the resistor and now there's a different reading its like ohm law...
  50. O

    Trying to see if I understand Ohms law

    Hello I'm trying to get my head around ohms law, and have a question. If I have a motor that draws 12volt 100amp, and I would like to drop the amps down to 30, would I put a 360ohm resister in line. 12 * 30 = 360 V * I = R Side note can you get a resister that is 480 watt...
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