What is Electric potential: Definition and 1000 Discussions

The electric potential (also called the electric field potential, potential drop, the electrostatic potential) is the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in an electric field with negligible acceleration of the test charge to avoid producing kinetic energy or radiation by test charge. Typically, the reference point is the Earth or a point at infinity, although any point can be used. More precisely it is the energy per unit charge for a small test charge that does not disturb significantly the field and the charge distribution producing the field under consideration.
In classical electrostatics, the electrostatic field is a vector quantity which is expressed as the gradient of the electrostatic potential, which is a scalar quantity denoted by V or occasionally φ, equal to the electric potential energy of any charged particle at any location (measured in joules) divided by the charge of that particle (measured in coulombs). By dividing out the charge on the particle a quotient is obtained that is a property of the electric field itself. In short, electric potential is the electric potential energy per unit charge.
This value can be calculated in either a static (time-invariant) or a dynamic (varying with time) electric field at a specific time in units of joules per coulomb (J⋅C−1), or volts (V). The electric potential at infinity is assumed to be zero.
In electrodynamics, when time-varying fields are present, the electric field cannot be expressed only in terms of a scalar potential. Instead, the electric field can be expressed in terms of both the scalar electric potential and the magnetic vector potential. The electric potential and the magnetic vector potential together form a four vector, so that the two kinds of potential are mixed under Lorentz transformations.
Practically, electric potential is always a continuous function in space; Otherwise, the spatial derivative of it will yield a field with infinite magnitude, which is practically impossible. Even an idealized point charge has 1 ⁄ r potential, which is continuous everywhere except the origin. The electric field is not continuous across an idealized surface charge, but it is not infinite at any point. Therefore, the electric potential is continuous across an idealized surface charge. An idealized linear charge has ln(r) potential, which is continuous everywhere except on the linear charge.

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  1. R

    What is the change in the proton's electric potential energy?

    Homework Statement A proton moves in a constant electric field E from point A to point B. the magnitude of the electric field is 6.4x10^4 N/C. The direction of electric field is opposite to the motion of the proton. If the distance from point A to point B is 0.50m, what is the change in the...
  2. C

    How Does Electric Potential Affect Proton Movement?

    Homework Statement Suppose that a metal plate is held at an electric potential of 1.8 Volts. A proton is placed on the plate where it is repelled by the plate. What is the electric potential energy of the proton measured in Joules? __ x 10-19 Joules After the proton has moved away from the...
  3. N

    How Do You Calculate Electric Potential for Spherical Shells?

    Electric potential probelm! HELP PLEASE TEST TMRW! Two uniformly charged spherical shells of radii R and 2R with identical surface charge densities σ are along the x-axis. The surface of each of the spheres is located a distance R from the origin O Define the potential at ∞ to be zero. Along...
  4. S

    Why Is a Negative Sign Used in the Electric Potential of a Charged Sphere?

    Hello, The electric potential is defined as: $$ \phi(\vec{r}) = \int d^3r' \frac{\rho(\vec{r}')}{|\vec{r} - \vec{r}'|}. $$ My question is, for solving for the potential inside of a charged solid sphere (constant charge density) by using the above equation I get, $$ \frac{Q}{2R} \bigg(...
  5. B

    Electric Potential and Potential Energy Due to Charged Particles

    Two charged particles of equal magnitude are located along the y-axis equal distances above and below the x-axis. Plot a graph of the electric potential at points along the x-axis over the interval -3a<x<3a. You should plot the potential in units of (KeQ)/a Let the charge of the particle...
  6. B

    Electric Potential in RC Circuits

    Hello, At the moment, I am writing the theory portion of my lab report. In the RC circuit, will the electric potential across the capacitor be at the same electric potential as the battery? Or will it depend on the voltage drop across the intermediate resistor?
  7. B

    How to calculate electric charge with a given electric potential?

    Hi! An iron plate with a mass of 1 kg surrounded by vacuum has an electric potential of +20 kV. How do I calculate the charge, Q of the iron plate? I have all the information I need, right?
  8. E

    Verification of electric potential

    Electric Potential at a point is defined as the "work done by the electric field on a charged particle as that particle moves in from infinity to point f"... My question now, is where does this electric field point. Consider a positive charge and we want to get the sign of V nearby. I know...
  9. E

    Qualitative meaning of electric potential

    Allright, when I say what is electric potential energy, someone will say it is kq1q2/r ... This answer doesn't satisfy me because what I am searching for is this.. Electric potential energy denoted by U is the work done by an external force to bring a charge from infinity to zero" ...That is why...
  10. E

    Confusion in electric potential energy

    This is an extract from my book ... " We define the potential V at any point in an electric field as the potential energy per unit charge associate with a test charge q0 at that point: V=U/q0." I don't know why did the book bring the test charge q0 now in the frame. Shouldn't the potential be...
  11. T

    Electric Potential and bounds of integration

    Homework Statement Find the potential difference between V(P) - V(R) and V(c) - V(a) Homework Equations Electric potential: V(a) - V(b) = \int^{b}_{a}E*dr V(b) - v(a) = -\int^{a}_{b}E*dr Fundamental Theorem of Calculus: F(b) - F(a) = \int^{b}_{a}f(x)dx The Attempt at...
  12. T

    Electric Potential of a Uniformly Charged Sphere

    My book gives the electric potential of a uniformly charged sphere as \frac{1}{4\pi \epsilon_0}\frac{Qr^2}{r_0^3}. I can't derive this forumula. What I get is \frac{1}{8\pi \epsilon_0}\frac{Qr^2}{r_0^3}. I can guess how the book did it which is by taking the equation for voltage of a single...
  13. J

    What is the electric potential energy of a proton

    Homework Statement What is the electric potential energy of a proton located 20.0 A (one angstrom or 1A is equal to 10^-10m) from another proton? Homework Equations Ep= F x d F= kq1q2/r^2 The Attempt at a Solution Ep= Fxd F=kq1q2/r^2 therefore Ep = (Kq1q2)(d)/r^2 d=r so...
  14. S

    Electric Potential Difference and electric field

    Homework Statement A uniform electric field points in the –y direction with magnitude 325 V/m. Find the electric potential difference VB-VA between the points A at (-0.200, -0.300) m and B at (0.400, 0.500) m. Homework Equations ∆V=-int(E . dl) (Dot Product) The Attempt at a...
  15. S

    Electric potential at the center of a insulating sphere

    Homework Statement Consider a uniformly charged insulating sphere with radius R and total charge Q in- side the sphere. If Q = 2.9 × 10−6 C, what is the magnitude of the electric field at r=R/2 K=columbs constant. The answer to this question is E=(K)(Q) / (2)*(R)^(2) The second...
  16. A

    Calculating Work Done by Electrical Force on a Moving Charge

    Homework Statement Two positive charges of q=3*10^-6 C are a distance 1 m apart. What will be the work done by the electrical force in bringing one of the charges to a distance of 0.5 m from the other charge (which is fixed at its position through the whole process)?Homework Equations The...
  17. B

    Electric Potential Drop Across A Resistor

    Hello, As a charge traverses through a resistive circuit element it will have a certain amount of potential energy before entering the circuit element; and as it passes through, it's potential energy will decrease (due to it converting to kinetic energy, and collisions)--this I iunderstand...
  18. N

    Electrical forces and energy: Electric Potential help

    Homework Statement Hi, I have a couple different problems that I did not understand. I have the images here. The problems which I did not understand were: 12, 13, 17. [EDIT: I calculated answer to 12 using conservation of energy.] For 13, I know how the graph looks; however, I'm not sure how...
  19. G

    Combined Electric field for two charges using electric potential

    Homework Statement Two equal and positive point charges Q1 and Q2 are a distance d from each other on the x-axis. Find the electric potential at the point P which lies a distance z on the z-axis from their centre. Then find the Electric field at the point, and then find the force F on a...
  20. S

    Resistance and Electric Potential

    This is probably a simple concept but I'm struggling a little bit understanding it. When power is dissipated through a resistor, how is potential actually lost? I understand energy is converted into heat and other forms, but isn't potential just defined as a function inversely proportional to...
  21. L

    Electric potential of a dipole moment

    Homework Statement The dipole moment of a water molecule is 6.29E-30Cm. What is the electric potential's magnitude 1.43nm from a water molecule along the axis of the dipole? Homework Equations p = qr The Attempt at a Solution I don't have values for q or r. I just know the...
  22. B

    Electric Potential Across Capacitors

    Hello, Suppose we have a battery, and there exists an electric potential difference between the positive and negative terminals, call it, V. When I attach a capacitor to the battery, will begin to charge, if it is initially uncharged. When the capacitor reaches its maximum charge, the phrase...
  23. J

    Electric potential inside a cube

    Homework Statement A metal box has 6 walls, all insulated from one another. The left and right wall are held at V= V0, which are at y=-d and y=d. All the other walls are grounded. The cube has dimensions where walls run from x=0 to x=2d, z=0 to z=2d, and y=-d to y=d. Homework...
  24. fluidistic

    Demonstration that the electric potential is continuous over a surface

    Homework Statement I'm asked to demonstrate that the electric potential is continuous over a surface with a charge density ##\sigma##. Homework Equations ##\Phi (\vec x )= \int _ S \frac{\sigma (\vec x' )}{|\vec x - \vec x '|}da'## The Attempt at a Solution I'm not sure what I must...
  25. S

    Electric potential reference points confusion

    Hi gang, I am hoping you can clear something up for me. When evaluating the potential of a solid sphere, I find myself confused about the volumes used such that, \phi = Q \int_{\infty}^R \frac{1}{V_1} r^2 \sin(\theta) \, dr \, d\theta \, d\phi + Q \int_R^r \frac{1}{V_2} r^2 \sin(\theta) \...
  26. B

    0 Electric potential between point charges?

    Can someone explain how you can have a zero electric potential between opposite charges? a charge would move there. I thought electric potential was the measure of energy per charge. wouldn't a 0 electric potential imply that a test charge cannot have any potential energy at this point? how is...
  27. J

    How do we pick where to set electric potential equal to zero?

    Sometimes we set potential to equal zero at infinity, other times at the origin. What's the general rule of thumb here-how do I know which to choose when doing a problem?
  28. fluidistic

    Electric potential using Green function, particular set up

    Homework Statement I would like to calculate the electric potential in all the space in the following set up: Conductor sphere of radius a whose surface is kept at a zero potential. 1 point charge ##q_1## at distance ##d_1## from the center of the sphere. 1 point charge ##q_2## at a distance...
  29. S

    Difference between Electric Potential energy and Potential energy

    Homework Statement A proton is released from rest in a uniform electric field of magnitude 8x10^4 V/m. After the proton has moved 0.5 meters a) What is the change in electric potential? b) What is the change in potential energy? c) What is the speed of the proton? Homework Equations...
  30. J

    Kinetic energy and speed of system of charges (electric potential)

    Homework Statement A square of side s has a point charge at each corner. They all have the same charge +q, but different masses, m1, m2, m3, and m4, respectively. Initially, all of the charges are held at rest until they are released. Of course, they would repel each other and move away from...
  31. M

    Two problems on Electric Fields and Electric Potential

    Homework Statement 1st Problem (a) Consider the electric potential V = C . r, where C is a constant vector. Find the electric field E(r). (b) For a given uniform electric field E = E(0)z^, using part (a) find the electric potential for this electric field...
  32. R

    Determining charge from electric potential

    Homework Statement A metal sphere with radius ra = 1.20 cm is supported on an insulating stand at the center of a hollow, metal, spherical shell with radius rb = 9.00 cm. Charge +q is put on the inner sphere and charge -q on the outer spherical shell. The magnitude of q is chosen to make the...
  33. M

    Comparing Electric Potential and Electric Field

    Homework Statement I guess this isn't like a homework question. I'm studying for an upcoming exam and feel pretty confident about most of the material, except for the relationship between Electric Potential and Electric Field. I guess the pertinent equation is as follows: Homework...
  34. L

    Electric Potential and Field

    Homework Statement A charge 36.41 mC is placed to the left of another charge 79.73 mC on a plane, as shown in the figure. Another charge of -8.051 μC and mass 14.31 g (depicted as a blue sphere) is placed at rest at a distance 16.34 cm above the right-most charge and released. What is the...
  35. M

    Electric Potential for Concentric Cylinders

    Homework Statement What is V(P) – V(R), the potential difference between points P and R? Point P is located at (x,y) = (50.0 cm, 50.0 cm). Homework Equations V=-∫Edl flux=∫EdA=Q/ε The Attempt at a Solution My attempt is in the attached photo to illustrate that I have worked the...
  36. M

    How do you find the electric potential from force?

    Homework Statement Suppose Coulomb's force is actually F= (y)(q1q2)(r hat)/(r^4) with y being a constant. Find the electric potential function V(x,y) for a charge Q located at the point x=a, y=b Homework Equations Fq=E V=integral (E)The Attempt at a Solution I am very confused by this...
  37. D

    When is Electric Potential equal to 0?

    Homework Statement A 3.03μC and a -1.93μC charge are placed 4.14 cm apart. At what point along the line joining them is the electric field zero? Assume that the first charge is at the origin and the second charge is at +4.14 cm. what points along the line joining them is the potential zero? Let...
  38. L

    Finding Electric Potential of concentric shells

    A thin spherical shell with radius = 3.00 is concentric with a larger thin spherical shell with radius 7.00 . Both shells are made of insulating material. The smaller shell has charge distributed uniformly over its surface, and the larger shell has charge distributed uniformly over its surface...
  39. S

    The electric field of a charged semicircle from its electric potential

    Homework Statement A question involving the relationship between the electric field E(r) and the electric potential V( r) is about computing the electric field on the z-axis due to a uniform line charge distribution λ spread out on a semicircle of radius R, lying on the first half of the XY...
  40. Q

    Electric Potential and Wave Nature of Matter

    Homework Statement An electric potential difference accelerates electrons from rest position towards a screen. Just before striking the screen, the electrons have a wavelength of 1.0*10^-11 m Find the electric potential difference.Homework Equations p=h/λ ΔEK=qΔVThe Attempt at a Solution...
  41. L

    Electric potential of tiny spheres question

    Homework Statement Two tiny metal spheres A and B of mass mA = 3.40 g and mB = 3.90 g have equal positive charges q = 4.50 µC. The spheres are connected by a massless nonconducting string of length d = 1.00 m, a distance that is much greater than the radii of the spheres. (a) What is the...
  42. N

    Electric potential problem with two plates and different points (i'll elaborate)

    Homework Statement There are two parallel plates. The plate on the left has an electric potential of +60 Volts. The right plate has an electric potential of 0 Volts. The plates are 8.0mm apart. Between the two plates lies a point P 2.0mm from the left plate with a charge -3.5pC. Point R lies a...
  43. P

    Space Dependence of Electric potential

    Homework Statement The space dependence of an electric potential V(\vec{r}) = V(x,y,z)=V0ln((sqrt{x2 + y2})/a) 1. What is the electric field at position \vec{r} = <x,y,z>? 2. Explain how the electric field looks in general. Make a sketch. 3. What object would produce an electric...
  44. D

    Electric Potential of a triangle?

    Find the electric potential at point P in the figure. http://i.imgur.com/8FNSoML.png V = kq / r So what I did was calculated the electric potential each force gives on the point P. Vp1 = (8.99e^9) (2.75e^-6) / .625 Vp2 = (8.99e^9)(-1.72e^6) / .625 Vp3 = (8.99e^9) (7.45e^6) /...
  45. O

    Electric Potential of Hollow Cone on z-axis

    Homework Statement This isn't a homework problem, but I got it off of an upperclassman's homework and decided to give it a shot. Consider a conical surface (like an empty ice-cream cone) with a height and top radius which are both h pointed up so that its axis lies along the z-axis and...
  46. B

    Electric potential at the outer surface of the insulating sphere?

    1.A solid insulating sphere of radius a = 3.6 cm is fixed at the origin of a co-ordinate system as shown. The sphere is uniformly charged with a charge density ρ = -218.0 μC/m3. Concentric with the sphere is an uncharged spherical conducting shell of inner radius b = 10.9 cm, and outer radius c...
  47. R

    Electric Potential Energy and Work

    Hello. I need help clearing up who's gaining potential energy and who's losing potential energy from an particular object perspective. And, from that object perspective, whether the object doing positive work or negative work. W = \int \vec F \cdot d\vec x \Delta U = -W Question 1...
  48. S

    Electric potential and Field Lines

    Sorry for any errors in posting, this is my first thread. Any help would be greatly appreciated! Homework Statement a.)On the contour map that is attached, find the magnitude of the electric field at each point A, B, and C. b.)Calculate the work done in moving a 1C positive charge from point A...
  49. M

    When is electric field zero and electric potential non zero

    Homework Statement Which one of the following statements about electric field strength and electric potential is incorrect? A Electric potential is a scalar quantity. B Electric field strength is a vector quantity. C Electric potential is zero whenever the electric field strength is zero. D...
  50. fluidistic

    Electric potential, getting coefficients, spherical harmonics

    Homework Statement Consider 2 conductor spherical shells of radii a and b (where a>b). The inner shell is at zero potential and the outer shell is at a potential given by ##V(\theta, \phi )=V_0 \sin \theta \cos \phi ## where ##V_0## is constant and theta and phi are the usual spherical...
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