Potential difference Definition and 701 Threads

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. cianfa72

    I Potential difference between a battery's terminal and Earth ground

    We had a similar thread some time ago. I'd like to reconsider some aspects. Consider a 9V battery just to fix ideas. The chemical electromotive force inside it establishes an amount of positive charges on its positive terminal and an exact same amount of negative charges on its negative...
  2. E

    I Does path independence still hold if permittivity is non-uniform?

    Consider a scenario in the picture where one half of space consists of a material with permittivity ϵ1 and the other half consists of a material with permittivity ϵ2, where ϵ1 > ϵ2. A unit positive charge is fixed at the interface between the two materials. Path1 is entirely within the material...
  3. M

    Sign conventions for Kirchhoff's loop rule

    Battery and Capacitor For a battery (or capacitor), the potential increases by ##\mathcal{E}## (or ##\displaystyle\frac{q}{C}##) as we move from -ve to +ve terminal (or plate) regardless of the direction of the assumed current. Resistor and Inductor Suppose we are traversing the loop in the...
  4. G

    I When to properly use "voltage"

    Hi. I'm confused about the usage of "voltage". Some scripts I read introduce it in electrostatic as potential difference (where there's only the scalar potential), but continue using it when changing magnetic fields are present ("induced voltage"). Others make a clear distinction and introduce...
  5. StarlitVarsh

    Need help with a question on potential difference

    So far, here's what I have: Taking the parallel-connected resistors alone, 1/Total effective resistance (R) = 1/3ohm + 1/6ohm = 1/2, so R = 2ohm Replacing the 3 and 6 ohm resistors with a 2 ohm resistor, the total resistance will be 2+4 = 6ohm Using V=IR, I (current) = V(potential...
  6. A

    B Why is potential difference the same across each branch in parallel?

    As the title says, i am struggling to understand how if the cell is only supplying 3V how 2 lamps in parallel both receive 3 volts (totalling 6) I currently study a level physics and never really questioned how this works and just accepted it as the truth. Can someone explain with a helpful...
  7. V

    Potential difference between 2 points in a capacitor circuit

    In the given circuit, a transient current will flow and when this current finally stops at equilibrium, the charges ##q_1## and ##q_2## are assumed to deposit at the capacitor plates as shown below. The dashed line indicates an isolated system that will have it's total charge conserved. If I...
  8. V

    Polarities of capacitor plates in a complex circuit

    (a) I think the top plate of C5 could end up with either + or - charge, and not necessarily + charge as shown. This is because the connected plates of C1, C5 and C3 form an isolated system to which we can apply the law of conservation of charge i.e. Total charge just before transient currents...
  9. Grizzly_1

    Gravitational equipotential multiple choice problem

    Hello everyone, thank you for taking your time to read this. I was assigned a homework task of multiple choice questions to do with gravitational fields. This is one of the last questions and I have been pondering over it for some time now. I don't understand how any sort of answer is...
  10. S

    Experiment about diode related to temperature and potential difference

    (a) I know some of the apparatus needed for the experiment, such as DC power supply, ammeter, voltmeter, maybe rheostat. But I don't know how to change the temperature of diode. What is the correct and safe way to change the temperature of diode? Thanks
  11. yucheng

    I Electric potential and potential difference

    Electric potential = "absolute potential" Textbooks usually connect both ends of two capacitors, of different voltages, in parallel. What would happen if we only connect one end of the capacitors? Perhaps we would have to solve for Maxwell's coefficients of potential for these two cases (to...
  12. homeworkhelpls

    Are lost volts the difference between EMF and terminal potential difference?

    Are lost volts the difference between EMF and terminal pd?
  13. M

    Finding charge on a capacitor given potential difference across two points

    For this part(b) of this problem, The solution is However, I tried solving (b) like this: Since ##Q_{total} = 363 \times 10^{-6} C## then ##Q_1 = 181.5 \times 10^{-6} C ## since the equivalent upper capacitor is in series with the equivalent bottom capacitor so should store the same amount...
  14. J

    Finding the potential difference in a circuit

    The solution chooses the centre wire to determine the potential difference, where Va−(0.909 A)(2.00 Ω)=Vb and Vb - Va = -1.82 If I choose the top wire (passing through the 12 V battery and 4 Ω resistor), Va - 12 + (1.636 A)(4.00 Ω)=Vb, and Vb - Va is different (= -5.46 V). Why would this path...
  15. N

    Acceleration of Uranium 238 ion through a potential difference

    I don't understand why the Uranium 238 ions are accelerated I think ##\Delta V = -2000 V## to accelerate since the ion would be accelerated by more postive charges so ## V_i > V_f ##
  16. T

    Hall effect over a conducting ring

    This is the diagram provided in the question: The ring is made of conducting material. I was originally asked to find the potential difference between ##a## and ##b##. I did so using the Hall effect (and assuming it would work as per normal in this situation). This got me ##\Delta V = vBl##...
  17. Ahmed1029

    I Is electromotive force always equal to potential difference?

    In the case motional emf, there is a static magnetic field and a rectulgular loop that goes into the field region, then current is produced. There is no electric field, but there is an emf. However, Griffiths states that emf is equal to the potential difference between the source endpoints. But...
  18. G

    Potential difference metallic sphere

    a) We know that ##Q_1=1,2\, \textrm{nC}## and ##Q_2=6\, \textrm{nC}##. By the TOTAL influence theorem: $$-Q_1=Q_{2i}=-1,2\, \textrm{nC}$$ $$Q_2=Q_{2i}+Q_{2e}\rightarrow Q_{2e}=7,2\, \textrm{nC}$$ b) Electric potential difference crust: $$V_A-V_\infty=$$ How was this potential difference thing...
  19. G

    Potential difference of an electric circuit

    The figure is: I have the solution to this problem: We have two distinct branches $$V_a-V_b=\overbrace{(V_a-V_c)}^{\textrm{INI}-\textrm{FIN}}+\overbrace{(V_c-V_b)}^{\textrm{FIN}-\textrm{INI}}$$ They have different intensities: ##3\, \textrm{mA}## and ##2\, \textrm{mA}## ##V_A-V_C\rightarrow##...
  20. L

    Calculating Electric Potential and Energy in a System of Spherical Conductors

    (a) Using Gauss's Law ##E_P=\frac{q_1+q_2+q_3}{4\pi\varepsilon_0(R_1+R_2+R_3+d)^2};(b) V_3-V_1=\int_{R_3}^{R_2}\frac{q_1+q_2}{4\pi\varepsilon_0 r^2}dr+\int_{R_2}^{R_1}\frac{q_1}{4\pi\varepsilon_0 r^2}dr=\frac{q_2}{4\pi\varepsilon_0}\left(\frac{1}{R_3}-\frac{1}{R_2}\right).## (c)...
  21. A

    Electric Potential Difference -- Conceptual Question

    I am able to get V1 = kq/a - 4kq/b and V2 = kq/b + -4kq/b For some reason the solution says it is V1-V2 as opposed to V2-V1. Maybe has something to do with positive shell in the center and negative outer shell? I know the electric field goes from positive to negative, but I don't know how...
  22. S

    Potential difference of a ring rolling in magnetic field

    I don't understand why there is potential difference between point A and O. Is there any change in magnetic flux experienced by the ring? I think the magnetic field passing through the ring's cross sectional area is constant Thanks
  23. nmfowlkes

    Potential Difference over Capacitors in Series

    V1 = Q/30 In parallel: C = C1 + C2 V2 = Q/(60 + 90) V1/V2 = 3 V1 = 3V2
  24. NoahCygnus

    Potential difference between two points in an electric field

    So I have been given a uniform electric field ##\vec{E}=20 V/m## in the direction as show in the image. I have been told to calculate the potential difference ##VC - VA##. According to the teacher (on YouTube) the potential difference ##VC - VA = -10\sqrt{2}V##. But I say it's ##-20 V## as...
  25. simphysics

    Single Loop Potential difference -- sign issue

    Hello everyone, I've been struggling with this problem for 1 hour so far. homework-and-exerciseselectric-cir
  26. kara123

    V/I: Power from Potential Difference & Current

    e=QxV t=Q/I p=(QxV)/(Q/I) =V/I The expression I came up with for a) is the potential difference divided by current to get power but I have no idea if that is even right if someone could just prompt me in the right direction that would be greatly appreciated
  27. Mr_Allod

    Depletion width of linearly doped PN-junction

    Hello there, I have derived the expressions for electric field and potential to be the ones above, then for continuity at ##x = 0## I set the electric fields and potentials to be equal to yield the expressions: $$Sx_p^2 = Kx_n^2$$ $$V_{bi} = V_n - V_p = \frac {q}{3\epsilon} \left( Sx_p^3 +...
  28. guyvsdcsniper

    EMF and how it's related to Potential Difference

    So Kirchoff's Loop law states that, The sum of all the potential differences encountered while moving around a loop or closed path is zero. Ok so that is basically a statement of energy conservation. So I see why in the TYPED solution, they related all voltages in the circuit equal to zero. I...
  29. guyvsdcsniper

    Trouble with negative sign in this Potential Difference problem

    So I know that E = -ΔV/Δs. If I wanted to solve for change in potential I could rearrange this equation and get Δ = -E*ds. With that information I believe I can solve the problem below. But in both solutions provided below, the negative sign goes away. Now I know I can pull the E out because it...
  30. T

    I How a Battery creates a Potential difference in an electrical current

    Hello, I'm seriously confused on several things around how concretely batteries create potential difference in order to force the electrons circulate trought the circuit wire. Almost all explanations I found (wikipedia, diverse tutorials, intro scripts, etc.) explain it in nearly the same...
  31. E

    Finding the potential difference between 2 points in a circuit

    is this method accepted? 2V is split equally between the 2 5kohms resistor because they are of equal resistance. 2V=5kohms 2kohms= 0.8V 3kohms=1.2V. p.d across P and Q= 1V-0.8V=0.2V
  32. oscarrod5

    Exploring Phase Potential Difference in 3-Phase Power

    I understand phase voltage (phase to neutral) well, but I'm still confused by what exactly the potential difference is between any 2 phases in 3 phase power. If you were to try to find the potential difference where 2 sine wave phases cross, then at that instantaneous point, the potential...
  33. Dario56

    I How is Potential Difference Created in Electrolytes?

    When we have a resistor in electronic conductors, potential difference is created via surface charges which accumulate on conductor surface. What about electrolytes? I am not sure if electrolytes can create potential difference in the same way since surface in electrolytic conductors isn't as...
  34. E

    Potential difference calculation

  35. V

    Find electric field intensity/density with given potential difference

  36. T

    POTENTIAL DIFFERENCE AND ELECTRIC FIELD HOMEWORK

    I tried following the formula but it wasn’t correct. I’m sure I could get it if I had an example as I’m sure this must be a simple question for other people I was just unsure if I was doing it correct.
  37. H

    Potential difference between the center of a sphere and a point 4.0 cm away?

    I can use integral as attached to obtain the answer. However, I wonder why I can not use " V = KQ / r " the get the correct answer. Thanks.
  38. S

    Potential difference across the ends of a solenoid

    Emf between the center of the disc and its rim = ##- \frac{d \phi}{dt }## = ##-B.A \frac{d \cos (\omega t)}{dt}## =##\mu_0 \frac{N}{L} I A \omega \sin (\omega t)## Potential difference across the ends of the solenoid = ##10\mu_0 \frac{N}{L} I A \omega \sin (\omega t)## Is this correct? How to...
  39. greg_rack

    Final electric potential difference in a circuit with two capacitors

    So, each capacitor must have a different potential difference, given by its capacity and charge... this would cause charge and current accordingly to flow in the circuit. But how do I determine the final potential difference, which would of course be the same for both of them? I have tried...
  40. greg_rack

    Electric potential difference at the ends of a resistor

    So, having two parallel resistor ##R_{1}## and ##R_{2}## , the current flowing through the equivalent one will be ##I_{eq}=I_{1}+I_{2}##. Now, it comes the point I'm not totally getting: why is ##V_{eq}=V_{1}=V_{2}##? These V's are the difference of potential measured between which points...
  41. greg_rack

    Clarifications about electric potential and potential difference

    Specifically, I haven't really got all the "methods" through which you could calculate or derive the electric potential and in some situations, I cannot understand how and when to apply this concept. Is it something caused by any charge, or must there be an interaction between the two to...
  42. P

    Position for maximum electric field between two wires

    For the first part, since $$ E(r) \propto \frac{1}{r} \hat{r}$$ by the principle of superposition the maximal electric field should be halfway in between the two wires. Then I'm not sure how to go about the second part of the question. I understand that the total potential due to the two wires...
  43. B

    Finding the potential difference of a diode

    I've tried doing it but i haven't been able to find the resistance of the diode.
  44. Kaushik

    Understanding EMF and Potential Difference in Electrical Circuits

    Is emf the work done to move a positive charge from LOWER potential to HIGHER potential to maintain the potential difference or else the charges move from higher potential to lower potential and will reach a point where the potential is the same between the two points and the charge will stop...
  45. S

    Potential difference between the surface of a sphere and a point far away

    V at surface = k Q / r = 9 x 109 x (1 x 109 x (-1.6 x 10-19) / (1 x 10-2) = - 144 V V at a point far away = 0 V From the sentence "electric potential difference between the surface of this sphere and a point far away" means that the question asks about V at surface minus V at far away so the...
  46. K

    Determine the Electrical potential at a given point

    A rod with a circular center in the middle (which causes the rod to change direction by 90 °) has an evenly distributed linear charge density 𝜆 of electrons along the entire rod. Determine the electrical potential of the red dot in the figure below which is at the center of the circular round...
  47. J

    Circuit Analysis of a diagram with series and parallel circuits

    I found the Req which is 13.6 and also found the It which is 0.74. I'm having trouble finding the separate current and potential difference numbers.
  48. nmsurobert

    Potential difference: positive or negative?

    I am working out an example problem from one of my textbooks and I am a bit confused on why a value is negative. The problem asks: Calculate the final speed of a free electron accelerated from rest through a potential difference of 100 V. This is a conservation of energy problem. Ultimately you...
  49. Tryhard314

    Salt water and potential difference

    Imagine a container of salt water at 0V (Relative to ground),Now you've put in it 2 electrodes,one at +500V (Electrode A), The other at +250V(Electrode b), Normally positive ions should go to the negative electrode , and Negative ions should go to the positive electrode , But in our example the...
  50. M

    Find the maximum potential difference across a series circuit

    I'm not really sure what I need to find exactly. From what I'm seeing, I could give C1 the max potential difference of 125V because it has the lowest capacitance, and because V = Q/C, this means the capacitor with the highest potential difference across its plates will be the one with the lowest...
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