What is Potential difference: Definition and 699 Discussions

Voltage, electric potential difference, electromotive force (emf), electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The old SI definition for volt used power and current; starting in 1990, the quantum Hall and Josephson effect were used, and recently (2019) fundamental physical constants have been introduced for the definition of all SI units and derived units. Voltage or electric potential difference is denoted symbolically by ∆V, simplified V, or U, for instance in the context of Ohm's or Kirchhoff's circuit laws.
Electric potential differences between points can be caused physically by electric charge build up or imbalance (eg. well known "static" and electronic capacitor) also by electric current through a magnetic field, and by time-varying magnetic fields (eg. dynamo or generator), or some combination of these three. Additionally on a macroscopic scale potential difference can be caused by electrochemical processes (cells and batteries) and pressure induced piezoelectric effect and heat induced emf across metal junctions. These latter processes at microscopic level have the physical origins previously mentioned. A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy (electromotive force) or lost, used, or stored energy (potential drop).

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  1. W

    Potential difference between three capacitors in series

    Hi, I'm having a problem with this circuit finding potential difference between capacitors. I know the answers by playing around on simulation software A=12v B=8v and C=4v however, I am struggling to use the formula provided Vc= (Vt/Ct)*C to find the answers. It works fine in a parallel circuit...
  2. 1

    (Answered) Finding new potential difference after switch is closed?

    Homework Statement The problem is: A 10.0-μF capacitor is charged to 15.0 V. It is next connected in series with an uncharged 5.00-μF capacitor. The series combination is finally connected across a 50.0-V battery as diagrammed in Figure P26.63. Find the new potential difference across the...
  3. X

    Why does the potential difference between two capacitors seek equilibrium?

    Suppose we have a circuit with two capacitors connected to each other, C1 and C2. C1 is charged and has a potential difference of 5 V (V1=5V), but C2 is not charged (V2=0) Apparently it is known that the potential difference of these two capacitors will want to reach equilibrium. So V1=V2...
  4. P

    Potential difference across two points in a circuit

    Homework Statement [/B] Find the potential difference between points b and a in the circuit below I have already solved for the voltages of the two batteries (1 and 2) in the circuit (18 V and 7 V respectively) 2. Homework Equations Kirchhoff's Rules 1) Potential difference across any...
  5. T

    Potential difference between wire and ground

    Homework Statement A long, straight power line is made from a wire with radius ra = 1.0 cm and carries a line charge density λ = 2.6 μC/m. Assuming there are no other charges present, calculate the potential difference between the surface of the wire and the ground, a distance of rb = 22 m...
  6. R

    Motion between two charged surfaces, find initial speed

    Homework Statement Two charged, parallel, flat conducting surfaces are spaced d = 1.3 cm apart and produce a potential difference ΔV = 625 V between them. An electron is projected from one surface directly toward the second. What is the initial speed of the electron if its comes to rest just at...
  7. G

    Voltage required for penetration of an unknown element

    Homework Statement An unknown element has a nucleus with charge 14.00 e and a radius of about 3.60×10-15 m. How much voltage must be used to accelerate a proton (radius 1.20×10-15 m) so that is has sufficient energy to just penetrate the unknown element? Assume that the potential is that for...
  8. 1

    Electric Field and Potential Difference in a Coaxial Cable

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  9. K

    Potential difference between a tube and a coaxial bar

    Homework Statement A capacitor made of a round solid bar and a thin round tube are coaxial, they are very long. the radii of the bar is ra and of the tube rb. they are both charged with λ, the charge per unit length, with opposite charges. what is the potential difference. Homework Equations...
  10. S

    Potential difference and current

    I have trouble understanding the internal resistance experiment in which potential difference decreases as current increases because I thought they are usually directly proportional to each other. Is there any concept that I am missing? I know that the lost voltage will be greater as current...
  11. S

    Calculate Potential Energy of Electron at a Parallel Plate Capacitor

    Homework Statement An electron with a speed of 5.0x10^6 m/s is injected into a parallel plate apparatus, in a vacuum, through a hole in the positive plate. The electron collides with the negative plate at 1.0x10^6 m/s. What is the potential difference between the plates? Vi= 5.0x10^6...
  12. D

    Potential Difference across a resistance

    Homework Statement a) Find Req of the circuit b) Find the potential difference across resistance R3[/B] Homework Equations Resistors in parallel = (1/R1 + 1/R2 + 1/R3 + ...)^-1 Resistors in series = R1 + R2 + R3 + ... The Attempt at a Solution a) R3 and R4 are in parallel --> [ (1/40Ω) +...
  13. G

    Calculating Potential Difference Between A & B

    Homework Statement Two points A and B are separated in space by distance dr. A has coordinates (x,y,z) and B has coordinates (x+dx, y+dy, z+dz). Using the definition of potential difference, show E = -\nabla\phi Homework Equations E = -\nabla\phi V = \int{^A_B}{E\cdot{dr}} The Attempt at a...
  14. D

    Potential difference due to two uniform sheet charges

    Homework Statement a) Derive the expression for the potential difference due to two uniform infinite sheet charges at y=5 and y=-5 in free space. b) If V=4V at (0,2,10) find V at (-4,3,1) . The surface charge density on the two sheet charges are ?s=?0 col/m2 [/B]Homework EquationsThe Attempt...
  15. D

    Potential difference due to two uniform infinite sheet charges

    a) Derive the expression for the potential difference due to two uniform infinite sheet charges at y=5 and y=-5 in free space. b) If V=4V at (0,2,10) find V at (-4,3,1) . The surface charge density on the two sheet charges are ?s=?0 col/m2 What you guys be able to help me with this ?
  16. R

    Minimum potential difference, Balmer series

    Homework Statement -A beam of electrons bombards a sample of hydrogen in its ground state. a) Through what minimum potental difference must the electrons be accelerated if only one line of the Balmer's series can be observed? Homework Equations V= h^2/2meλ^2 (V=potential difference)...
  17. P

    Find the potential difference in a rectangle

    Homework Statement [/B] Figure 20-3, referred to below, is 0.800m wide and 0.400m tall with "A" in the top left corner, "+4 microC" charge in the top right corner, "+2 microC" charge in the bottom left corner, and "B" in the bottom right corner. Two point charges of magnitude +4.00 μC and...
  18. M

    Finding current and potential difference within a circuit

    1. For the circuit shown, (a) Find the current in each resistor (b) Find the potential difference between c and fHomework Equations :[/B] i2 + i1 = i3 i = V/R3. (a) So solving for each resistor using the loop rule this is what I got, (Resistor 3): E3 - IR3 = -E2 - E1 (Resistor 2): -E2 - IR2 =...
  19. D

    Potential difference to acquire momentum

    Homework Statement Electron diffracation experiment show that the wavelength of a electron is 0.15nm. Find the momentum of the electron in the beam. ii) Through what the potential diffrenece should the electron accelerated from rest to acquire this momentum? Homework EquationsThe Attempt at a...
  20. K

    Potential Difference: Electron Accelerated to Relativistic Speed

    Homework Statement An electron accelerated from rest through a potential difference V acquires a speed of 0.8c. Find the value of V. Homework Equations E=(gamma)mc^2, E=Vq The Attempt at a Solution For this I related the two equations above and chose a value of m=0.5MeV for the electron and...
  21. A

    Potential difference between two spherical conductors

    I'm working my way through MIT 8.02x on EdX (an archived course, so it's a bit lonely in there right now!). The problem statement: Two spherical conductors, A and B, are placed in vacuum. A has a radius rA=25 cm and B of rB=35 cm. The distance between the centers of the two spheres is d=225...
  22. D

    Potential Difference in Circuits

    In the picture that i attached i need some help ******** In the book it says ''' The negative terminal of the battery E_1 is connected to b. So at the lower end of the resistance R_2 the pd is 6V. "' What is the significance of this statement?
  23. A

    Electrical potential and potential difference

    Indian school books say -- We define the electrical p.d. between two points in an electrical circuit carrying some current as the work done to move a unit charge from one point to other! =>V=W/Q But, my doubt is...since work done is directly proportional to distance between two points...
  24. B

    Speed of electron accelerated by a potential difference

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  25. A

    Potential difference in uniformly charged cylinder

    Homework Statement Charge is uniformly distributed with charge density ρ inside a very long cylinder of radius R. Find the potential difference between the surface and the axis of the cylinder. Express your answer in terms of the variables ρ, R, and appropriate constants. Homework Equations...
  26. V

    Volume charge density across a potential difference

    Homework Statement A 1.0 μA proton beam is accelerated across a potential difference of 1.0 kV. Assume the beam has uniform current density over a diameter of 2.0 mm, and zero outside. Find: volume charge density in the beam, (HINT use λ=I/v where λ= charge/ unit length) The radial...
  27. Rugile

    Rotating rod - potential difference between the ends

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  28. R

    Potential difference between two infinite cylinders

    Homework Statement Find the potential difference between two oppositely charged, infinite cylinders of radii R whose axes lie at $$y =+\frac{d}{2}$$ and $$y = -\frac{d}{2}$$ They have surface charge densities of magnitude $$\sigma$$ Homework Equations The family favourite - Gauss' Law...
  29. kartikwat

    Potential difference and battery

    How does a battery creates a potential difference and what is the intuative way to look at potential difference when studying capacitance
  30. C

    Find the potential difference between 2 junctions (nodes)

    Hello, I'm wondering how to determine the value of the potential difference between two points (junctions specifically) in a circuit with 2 emfs. The junctions are points x and y in the circuit below. I thought I could use the junction rule to determine the current at each junction...
  31. J

    How Does Battery Voltage Indicate Electric Potential Difference?

    If a battery has 6V of voltage, this means that P+ – P– = 6V or that P– – P+ = 6V ? Being: P+ = electric potential of the positive pole P– = electric potential of the negative pole
  32. 22990atinesh

    Calculating Potential Difference

    Homework Statement Two capacitors ##C_1## and ##C_2## (where ##C_1 > C_2##) are charged to the same initial potential difference ##ΔV_i##, but with opposite polarity. The charged capacitors are removed from the battery, and their plates are connected as shown in Figure a. The switches...
  33. G

    Potential Difference and Power in Resistor Circuit

    Homework Statement I attached a screenshot of the problem(s) that my professor gave in a practice exam. Homework Equations ∑I = 0 at each junction ∑V = 0 at each closed loop P = I2R = V2/R Rseries = R1 + R2 +... The Attempt at a Solution Part A: I think the current I in the center...
  34. R

    Potential Difference between conductors for a coaxial cable, conflict

    conflicting results. find the potential between the two conductors of a coaxial cable I have already found E... E = lambda / 2 pi r epsilon my question: What are the integration limits for finding the potential between the conductors? say we have a radius a (inner conductor)...
  35. T

    Infinite Line of Charge and Electric Potential Difference

    Homework Statement 1. Consider a line of charge (with λ charge per unit length which extends along the x-axis from x=-∞ to x=0 (a) Find all components of the electric field vector at any point along the positive x-axis (b) Find the electric potential difference between any point on the...
  36. M

    Potential difference question - Immediate

    The emf and internal resistance are shows in the attached image. When the terminal voltage, Vba, is equal to -40V, what is the current through the battery, including its direction? Solution: VT = emf - iR (general) In this case, VT = 40V, when considering VT = Vab = Vb - Va VT =...
  37. M

    Potential difference in a single battery

    When we place a voltmeter across a single battery which is connected to another battery in series, does voltmeter show the emf of the single battery or the sum of emf of both the batteries?
  38. K

    What does 0 electric potential difference mean?

    This isn't a homework question, but while working on some questions in Physics AP C, I've come across several questions involving 0 PD (potential difference). My question is simple; what does 0 PD mean? so far i know that 0 potential difference of any kind is arbitrary, since it represents the...
  39. K

    Determine potential difference (circuits)

    Homework Statement Va - Vb Homework Equations V = IR Loop rule Node rule The Attempt at a Solution I'm able to find each I value, as well as the direction of current. I'm not sure what to do after that. I know the answer should be 45V, but everything I've tried doesn't lead to that.
  40. M

    Potential Difference in case of electrons

    If the potential difference between point A and point B is 10 Volts, then when a unit positive charge passes from A to B, the charge loses 10 J of energy. But when an electron passes from A to B does it gain energy, because in W = Q . V , Q is negative. I am really confused in potential...
  41. G

    What causes potential difference in the conductor?

    What cause potential difference in the conductor? I mean why the changing magnetic flux induce EMF? I understand the basics but I can't understand it. What I know: there is free electrons on the surface of a copper conductor. Electron have electric field vector and magnetic field vector and...
  42. K

    Electric potential difference vs. voltage drop

    Are these the same thing? Or does the electrical potential difference refer to the voltage source only?
  43. L

    Potential Difference Across Resistor in Parallel with Inductor

    If we have a resistor and inductor in parallel, how does the resistor maintain a potential difference equal to our emf? Am I correct in saying that for the inductor to maintain a voltage difference, there has to be some change in current, so that the current going through the resistor is also...
  44. B

    Potential Difference and Current

    Homework Statement Wires 1 and 2 are identical except that they are each made of a different material. The one end of wire 1 is connected to one end of wire 2. The two remaining ends are connected across a battery and current flows through the two wires. Is the potential difference is wires...
  45. D

    Stationary Electron accelerated through potential difference

    I have this question that asks what the velocity of the stationary electron is after being accelerated by potential difference. The potential difference is 500v, but the specific potential difference doesn't concern me. I'm uncertain of how i get the velocity, because i don't know an equation...
  46. M

    Potential Difference problem with sphere and capacitor

    Homework Statement A thin spherical shell made of plastic carries a uniformly distributed negative charge -6e-10 coulombs (indicated as -Q1 in the diagram). Two large thin disks made of glass carry uniformly distributed positive and negative charges 1.5e-05 coulombs and -1.5e-05 coulombs...
  47. L

    Potential difference battery

    Homework Statement How can I measure the potential difference across two batteries? For example, if I put the batteries end to end, so the negative end of one touches the positive end of the other. And let's say both batteries have 3 volts and let's denote point A to B as the point from one...
  48. M

    Two-conductor transmission line, find the potential difference V of th

    https://www.physicsforums.com/attachments/66302Two-conductor transmission line, find the potential difference V of the two conductors.? Two-conductor transmission line. At point P (x=43 cm, y=32 cm) in Fig. 2-10, |E|=450 V/m. If s=25 cm, h=29 cm, and r=12.5 cm, find the potential difference if...
  49. J

    What potential difference is required to bring the proton to rest?

    Homework Statement A proton has an initial speed of 4.9 105 m/s. (a) What potential difference is required to bring the proton to rest? (b) What potential difference is required to reduce the initial speed of the proton by a factor of 4? (c) What potential difference is required to...
  50. U

    Donnan equilibrium -how is the potential difference caused?

    So I was watching a video about Gibbs-Donnan equilibrium () On one side of the semipermeable membrane, there is a solution of potassium ions and impermeable protein ion (negative 1 charge). On the other side there is potassium chloride. It said that after the electrical and chemical...
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