What is Voltmeter: Definition and 151 Discussions

A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit.
Analog voltmeters move a pointer across a scale in proportion to the voltage measured and can be built from a galvanometer and series resistor. Meters using amplifiers can measure tiny voltages of microvolts or less. Digital voltmeters give a numerical display of voltage by use of an analog-to-digital converter.
Voltmeters are made in a wide range of styles, some separately powered (e.g. by battery), and others powered by the measured voltage source itself. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus. Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant.
General-purpose analog voltmeters may have an accuracy of a few percent of full scale and are used with voltages from a fraction of a volt to several thousand volts. Digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million. Part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. In laboratories, the Weston cell is used as a standard voltage for precision work. Precision voltage references are available based on electronic circuits.

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  1. O

    Calculating Correct Voltmeter Reading in a Circuit

    Homework Statement The voltmeter in the figure below reads 6.2 V. If the vs = 12 V and R1 = 560 Ω, R2 = 470 Ω, R3 = 680 Ω, and R4 = 4.7 kΩ, is the voltmeter reading correct? Homework Equations V*Rx/(Ry+Rx) The Attempt at a Solution So I thought the voltage in the voltmeter would equal the...
  2. learnings_sweet

    Finding terminal voltage without voltmeter

    << Mentor Note -- OP has been warned about not showing any effort toward a solution >> 1. How can I find the terminal voltage across a 6v power supply, without using a voltmeter. The problem is the only equipment listed on the practical is an ammeter and a resistor with unspecified...
  3. SalfordPhysics

    Helmholtz Resonator using voltmeter

    Hi, I am trying to understand how precisely a voltmeter is used to measure the resonant frequency of a sound wave in a helmholtz resonator. Is it simply that the maximum voltage corresponds to the resonant frequency? A detailed description or external link would be great. Many thanks.
  4. N

    What's the point of a voltmeter having a high internal resistance?

    Homework Statement I understand that voltmeters are supposed to have high internal resistances so that they won't draw much current. However, they are being attached parallel to the resistor anyways and according to Kirchhoff' Law that means the voltage through both the resistor for which we...
  5. Entanglement

    The voltage across a voltmeter Olymp 09

    The question I'm asking about is Olymp 09 My attempt : 2.36 V Vb1 / (R + r1 + r2) = 2 / 2.5 = 0.8 A Vb2 / (R + r1 + r2) = 5 / 2.5 = 2 A The reading of the voltmeter = the voltage across r1 + the voltage across r2 and R = (0.8)(2.2) + (2)(0.3) = 2.36 V I'm not sure of my answer, and even...
  6. Rugile

    Calculating Voltages Across Resistors Using Ohm's Law

    Homework Statement Two resistors are connected in series to an ideal battery. When the voltmeter is connected in parallel to one of the resistors, it showed 6V; when connected in parallel to another resistor it showed 4V. When the voltmeter was connected in parallel to both resistors...
  7. B

    Voltmeter Readings: Changes with Contact Resistance Increase

    When the contact surface between two conductors is increased, (battery and wire) what happens to the voltmeter reading? If cross-sectional area of wire is increased, current increases but what happens to potential difference on the circuit? Contact resistance is what's varying surely... or...
  8. J

    Data Logging for Voltmeters: How to Save and Read Data Using an Arduino

    Attaching a data logging system to a voltmeter: Produino ST Master Chip 0.56" LED DC 3-Digital Display Digital Voltmeter- Black (DC 0~100V) Goal: I want to save the data from the voltmeter over time with a ± 10Hz sampling rate, logging this on a SD card or UBS stick, making it able to...
  9. P

    Voltmeter connected across an open switch

    I have once read that if a voltmeter is connected across an open switch in a circuit, the emf of the source is shown on the voltmeter, because this connection completes the loop, making a tiny current flow through the circuit, and since the voltmeter has a huge resistance, the entire voltage...
  10. Saitama

    Reading Voltmeters: Constant Terminal Voltages & Resistances

    Homework Statement The terminal voltages of the power supplies shown in the figure are constant, and the values of the terminal voltage are: ##U_1=15 V## and ##U_2=45 V##. The resistances of the resistors are ##R_1=10 \Omega## and ##R_2=20 \Omega##. a) What are the readings shown by the...
  11. P

    Building a homemade crank generator, but no voltage on voltmeter?

    Hey guys, I built up this design for a hand-powered crank generator with four neodymium magnets, but am having trouble getting a reading through a voltmeter. I want to try and amplify the voltage as well but that will come later. Here is our setup http://imgur.com/a/0aM4W#0 I am not...
  12. A

    Converting a galvanometer to ammeter and voltmeter.

    How will you convert a galvanometer of resistance 12 ohms showing full scale deflection for a current of 3 milli ampere to (i) Ammeter of range o to 6 Ampere (ii) Voltmeter of range 0 to 18V.
  13. M

    Voltmeter relative error question. (Computer Controlled Measurement)

    Homework Statement You measure 50V with a voltmeter, which has 300V as the max. input voltage. What will be the relative error (h%) of the measurement? Homework Equations The Attempt at a Solution hi i divided 50v / 300 V and get = 1,66 and divided it by 100 to get relative error...
  14. N

    Voltmeter: Concept of Letting Rg Be Resistance of Galvanometer

    let Rg be the resistance of the galavanometer. A formula in my book states that V=Ig(Rg+R) my doubt is: here Ig(Rg+R) is the potential drop across the two resistors of the voltmeter. But how can this include the potential drop by the circuit element across which the voltmeter is connected.
  15. L

    Calculating Rx for a 0 Reading on Voltmeter - Ohm's and Kirchhoff's Laws

    Homework Statement In the diagram, attached to this post, what is the value of Rx in relation to R1 R2 and R3 so that the voltmeter would show 0? Homework Equations Ohm's law and Kirchhoff's laws I suppose. The Attempt at a Solution I have thought about this thing for too much now...
  16. E

    Voltmeter in Series as self inductance of cables is significant

    Hello, I am using a lock-in amplifier to measure the AC voltage across a small sample of superconducting wire located in a cryostat. As the self-inductance and the capacitance of the wires used for the measurement are non-negligible, I have basically connected the lock-in amplifier in series...
  17. O

    Circuit Analysis: Current and Voltage Ranking

    Homework Statement Consider the circuit at right, consisting of two identical resistors (R1 and R2) and a red LED. The battery is ideal and maintains a constant voltage of +9.0 V (i.e., V1 - V2 = +9.0 V). An ideal voltmeter is connected across the LED and R2. 1. At point a, is the direction...
  18. R

    Solving Electrical Circuit Puzzle: Voltmeter & Transistor

    Homework Statement http://web.stagram.com/p/362176186041336029_243276631 this is a link to the question. I'm stuck on 2a and b Homework Equations I don't understand if the voltmeter is reading 6v why the light is not receiving 6v? And why would a transistor help this problem? The...
  19. Y

    Does a voltmeter read emf of a battery if its resistance approaches infinity?

    Now for this case when the voltmeter is not a ideal one, a small current is flowing. The voltmeter reading equal to the potential difference across itself (10V) and not emf of the battery(12V) . This happens because there is current flowing through the whole circuit, causing IR to exist across...
  20. J

    Archived How to include resistance of wire and voltmeter in Kirchhoff equations

    Homework Statement I'm doing a lab report and the last question is, how would your measurements (currents and voltages across each resistor) be affected if the resistance of the wires is 0.01 Ω and the internal resistance of the voltmeter is 10 MΩ? Homework Equations The Attempt at a...
  21. S

    Medical Voltmeter registers on my skin

    Can anyone out there tell me why a voltmeter would strongly register when I touch it to my arm, and yet I am in no contact with any electrical current? This seems outrageous to me. It is a commercially available pen tester bought at Home Depot and set on the highest setting.
  22. D

    Engineering Voltmeter in simple battery + resistor circuit

    Homework Statement Find the current in the circuit and the voltage on the volt meter Homework Equations E=22.5 V Rtot= 1kΩ + 2.4kΩ + 5.6kΩ = 9kΩ I=U/R=22.5V/9kΩ=2.5mA A voltmeter has super high resistance, to prevent any current from passing through it. I know that. So I have...
  23. S

    Why Do Voltmeter Readings Differ in a Series Circuit?

    Homework Statement A person measures 9volts across the battery, 3 volts across the resistor Ra and 4.5volts across the resistor Rb connected in series (all three battery, Ra, Rb are connected in series) with a voltmeter of finite resistance. The resistor Ra=2M, and the battery has negligible...
  24. W

    Purpose of capacitor in the ICL7107 voltmeter circuit

    Hi, I was wondering what is the purpose of connecting 0.01 micro farad capacitor across pin 30 and pin 31 of the circuits http://www.electro-tech-online.com/custompdfs/2012/07/fn3082.pdf(page 11 to page 12 every typical circuit does connecting it) ? I have tried to read through the datasheet...
  25. W

    Application/Use of 200mV scale in voltmeter

    I was wondering what are the uses of 200mV scale in voltmeter? I mean isn't it too small for most applications? but it seems to me every meter has such small scale ,so I was wondering what is their actual usage?
  26. W

    ICL 7107 digital voltmeter helps needed

    I'm building ICL 7107 digital voltmeter with 200mV full scale as Figure 12 (page 11) on http://www.intersil.com/data/fn/fn3082.pdf. Here is the problem I'm facing: it shows random numbers, sometimes showing 1666, and it has no effects even when I try to calibrate by adjusting the...
  27. L

    Why is the voltmeter connected in series in electrolysis?

    Hi guys, I was wondering, in the process of electrolysis when we are looking at a galvanic CELL, meaning a battery, why is it that when we want to measure the voltage caused by using the two metals of different elements, we connect the voltmeter in series to the external circuit? If you...
  28. A

    Circuits: What does the voltmeter read?

    Homework Statement A E = 12.0V battery with an internal resistance r = 1.80Ohm is connected to two 8.80kilo-Ohm resistors in series. An ammeter of internal resistance 0.410Ohm measures the current exiting the battery and at the same time a voltmeter with internal resistance 17.7kilo-Ohm...
  29. T

    Finding Resistance of a Voltmeter

    Homework Statement I'm trying to find the internal resistance of a Voltmeter. The current is 0.212 mA which is measured by I. Rx is 7000 Ohms and the emf of the battery is 1.50 V. Homework Equations V = IR so R = V/I The Attempt at a Solution How can I start it off to find the...
  30. B

    Calculating Voltage Drop and Current Through a Voltmeter

    Homework Statement Voltmeter has a internal resistance of 10M ohms and the resistor has a resistance of 100,000ohm. The current through the resistor is 1mA. a)What is the voltage drop across the voltmeter? b)What is the current through the voltmeter? Homework Equations V=IR is all you...
  31. S

    Calculate Apparent & Actual Resistances of Unknown Resistor

    Hi there, this is one of the question of my assignment. A voltmeter with a sensitivity of 1000 Ω/V has a full scale deflection of 150V. When connected across an unknown resistor in series with a milliammeter, it reads 100V. If the milliammeter reads 50mA, calculate the following: a...
  32. T

    Level of johnson-Nyquist noise in analog voltmeter

    Hello, I was wondering if anybody could answer a quick question: What is the typical level of Johnson-Nyquist noise in an analog voltmeter in equilibrium (short circuited)? Is it millivolts? What is the level for an AC current of order mA at 50Hz?
  33. J

    Role of a voltmeter in an initially open circuit

    Hi! Could someone briefly explain the following scenario to me please :) If an open circuit (with the 2 ends named X and Y) hung on a string is swung through an into page magnetic field, what would the emf be? How would that change if you are asked about the voltage 'measured' between X and Y...
  34. V

    Ammeter and Voltmeter question?

    Homework Statement A ammeter and a voltmeter are joined in series to a cell . Their reading are A and V respectively. If a resistance is now joined in parallel with voltmeter, (a) Both A and V will increase (b) Both A and V will decrease (c) A will decrease V will increase (d) A will increase...
  35. S

    Solve emf of battery with resistors and voltmeter

    Homework Statement Two 9.4 k-ohm resistors are placed in series and connected to a battery. A voltmeter of sensitivity 1000 ohm/V is on the 3-V scale and reads 2 V when placed across either resistor. What is the emf of the battery? (Ignore it's internal resistance) Homework Equations...
  36. G

    Solving a Circuit: What Will the Voltmeter Show?

    Homework Statement http://imageshack.us/m/508/9977/unlednia.png The emf source resistance is equal to the bulb's resistance. The voltmeter has some big resistance and it shows 6volts. What will the voltmeter show when the bulb burns out ? Homework Equations I think...
  37. 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?
  38. F

    Negative voltage and voltmeter

    Hello Forum, maybe not a new topic but let me ask anyway. The voltmeter is a simple device used to measure voltage or potential difference. Take a 9 Volt battery. If we connect it to a voltmeter the reading could be either +9 V or - 9 V. What makes one of the leads of voltmeter different...
  39. Femme_physics

    Voltmeter must cause disconnnection in order to measure the volt?

    We learned yesterday that a voltmeter's resistance approaches infinity. And that infinite resistance means total disconnect. I'm trying to understand why is that? Why must a voltmeter's resistance approach infinity? Doesn't it mean that the voltage will be 0? BTW - I hope I'm translating...
  40. A

    Am i right?Voltmeter Question: Is R Greater or Less than 5ohm?

    Voltmeter question... Homework Statement A student connects an Ammeter A and a Voltmeter V to measure a Resistance R as shown in attached diagram...If the Voltmeter reads 20 V and the ammeter reads 4A then R is 1. equal to5 ohm 2. Greater than 5 ohm 3. Less than 5 ohm 4. Greater than or...
  41. E

    MATLAB DIY Voltmeter: Build Your Own Card for MATLAB Plotting

    Hi, I recently got it into my head that I would like to make an analog-digital interface card for my laptop such that I can plug two wires into the card and have the the card send data on the potential difference between the two wires to my laptop via the USB port. The plan is to then have...
  42. I

    Optimizing Voltage Measurement in High Resistance Circuits

    What is the best way to measure the voltage from a high resistance circuit? The circuit resistance is higher than the resistance of the voltmeter.
  43. T

    What is the Voltage read on a Real Voltmeter?

    Homework Statement The output of the voltage-divider network shown in the diagram below is to be measured with two different voltmeters, V1 and V2. Consider the situation when V0 = 32.4 V, R1 = 205 Ω, and R2 = 465 Ω. a) When the voltmeter V1, whose internal resistance is 4.80 k Ω is placed...
  44. T

    Voltmeter Problem Homework: Is My Answer Correct?

    Homework Statement The Attempt at a Solution I think that the AVOM meter would act as a better voltmeter. This is because it has a higher meter resistance, meaning that it is more sensitive. Therefore, it will disturb the circuit as little as possible and it will draw less current to...
  45. I_am_learning

    Working of True RMS analog voltmeter?

    How does a True RMS analog voltmeter work (if it exists)? (I am not interested about digital Sampling methods) I have heard about 'absurd' methods like heating up a coil through the sample voltage and using a thermocouple driven simple DC voltmeter to give the reading proportional to the...
  46. 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...
  47. A

    How does a ammeter and voltmeter works?advanced thanks.

    how does a ammeter and voltmeter works? advanced thanks.
  48. A

    Resistance of ammeter and voltmeter

    Homework Statement http://img638.imageshack.us/img638/2421/screenshot20100807at012.png Homework Equations The Attempt at a Solution For the ammeter resistance i chose to find the difference in the voltmeter reading in the two circuits. that difference is the p.d. across the...
  49. S

    Quick question on connecting ammeter, voltmeter

    first if i were to connect an ammeter i would connect it in a series correct? if i connect the ammeter in parallel what would happen? second if i were to connect a voltmeter i would connect it in parallel? if i connect the voltmeter in series what would happen?
  50. G

    LC Parallele Voltmeter problem

    http://img295.imageshack.us/img295/6016/55877904.th.jpg I tried everything to solve this. XL and XC are an inductor and a capacitor (respectively). I start with the idea that there are 50 V on each of them, and that a current of 5 A flows between, and that the generator has no effect, because...
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