# Potential difference Definition and 56 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. ### 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##...
2. ### 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...
3. ### 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##...
4. ### Three 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)...

7. ### EMF vs Potential difference

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...
8. ### 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...
9. ### 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.
10. ### Electric field in a circuit with a DC source

So I understand that when an electric field is produced in a conductor of length L, the net electric field in the conductor will be 0 because the rearrangement of electrons in the conductor results in the production of its own electric field which cancels out the one produced initially...
11. ### Potential difference in a 2 disk system (Capacitor)

Homework Statement A capacitor consists of two large metal disks placed a distance ##s## apart. The radius of each disk is R ## (R \gg s)## and the thickness of each disk is ##t##. The disk on the left has a net charge of ##+Q## and the disk on the right has a net charge of ##-Q##. Calculate...
12. ### Final potential difference of a 2 capacitor system

Homework Statement An isolated parallel-plate capacitor of area ##A_1## with an air gap of length ##s_1## is charged up to a potential difference ##\Delta V_1## A second parallel-plate capacitor, initially uncharged, has an area ##A_2## and a gap of length ##s_2## filled with plastic whose...
13. ### Floating potential of a conductor in an electrical field

I'm interested in the following general question: Assume x,y,z is an axes system, and that the y-z plane is occupied by a conductive plate at a known potential V with respect to the earth. Now, a conductive material M of neutral global electrical charge is placed at some distance of the plate...
14. ### Gravitational Potential Reference Point

Can someone please show that calculation of gravitational potential energy at a point R+h from the centre of the Earth by choosing the centre of the Earth to be at zero potential. Here R is the radius of the Earth and h is not very small wrt to R
15. ### Which way do I measure the potential difference

Homework Statement All the bulbs in the circuits are identical, as are all the batteries. Rank the magnitude of the potential difference between points M and N. Homework Equations V=IR The Attempt at a Solution My most fundamental question is actually which way do I know to take the...
16. ### What is the potential of plate B with respect to infinity?

I have two isolated plates A and B, kept parallel to each other. Now I give charge +Q to the plate A, it will redistribute itself as +Q/2 on the outer plate A and + Q/2 on the inner plate A. Right? Now this will induce charge -Q/2 on the inner plate B and +Q/2 charge on the outer plate B...
17. ### Potential and Electric Field

Homework Statement A potentially silly question that I have put off too long to ask, any assistance is greatly appreciated! The electric field evaluated along the Z axis of a ring of charge centered on the origin and lying on the XY plane is only a function of ##z## and points only along...
18. ### Potential Difference/Voltage-Graph Help Needed (Long)

Homework Statement Alright, this is a Lab Exercise, so it's light on an actual introduction and data, but I'll do my best to put into words the whole thing. The gist of it is that we have a Vat with water, a millimetre paper at the bottom, and we put two Equipotential surfaces inside. We charge...
19. ### Parallel plate electric fields -- # of electrons transferred

Homework Statement An oil droplet is suspended between two horizontal parallel plates with a separation of 0.4 cm. If the potential difference of 320V is applied to the plates, determine the number of electrons transferred to/from the droplet. Given/Known Values mdroplet = 5.2×10-6 kg d = 0.4...
20. ### Confirming my logic on potential difference

Homework Statement You’ve decided to protect your house by placing a 5.0 m tall iron lightning rod next to the house. The top is sharpened to a point and the bottom is in good contact with the ground. From your research, you’ve learned that lightning bolts can carry up to 50 kA of current and...

So I understand that a capacitor consists of 2 plates separated by a distance which creates a potential difference between the plates. But I was confused, when watching this physics video it seemed to be saying that once the capacitor was fully charged, the plate closest to the positive terminal...
22. ### Voltage in terms of a battery

I'm trying to understand what exactly it means in terms of the voltage of a battery. I know that the voltage in a battery is just the potential difference between the two terminals. But, is the negative terminal used as a relative point and seen as 0? If that's the case does 12V mean that the...
23. ### Potential Difference b/w concentric shells -- confusion

Homework Statement :[/B] This is isn't exactly a problem,but actually something i don't understand in the book i was following, so there this art. about 'Principle of a Generator', whose description is given as, " A generator is an instrument for producing high voltages in the MeV range. Its...
24. ### Magnetic Fields- Finding the radius

Homework Statement A single ionized uranium ion of mass 6.9 x 10 ^-25 kg is accelerated through a potential difference of 4.4 x 10^5 V. What is the radius of the path it would take if injected at 90 degrees into 0.47 T uniform magnetic field at this velocity? 3. Attempts Since centripetal...
25. ### Potential difference between two points

Homework Statement Question from OCR A Level Physics Exam 2014 (i) and (ii) = definitions (iii) = explanation (iv) = P.d. at 6Ohm Resistor = 0.48V (v) Suggest why the p.d. between X and Z is zero Homework Equations I don't think there are any The Attempt at a Solution I couldn't...
26. ### Why do the capacitors in this circuit have the same voltage?

Homework Statement Homework Equations C = Q/V The Attempt at a Solution I understand that capacitors in parallel have the same voltage, but wouldn't they be in series after the switch is flipped, since no current goes to the left most portion of the circuit.
27. ### B How to remember what happens to I, V and R in a circuit?

There are two circuits, each consist of a cell and two bulbs, in one circuit they are in parallel, and in the other they are in series. What's the best way to remember which lamp has the greatest pd, current and resistance when one bulb is brighter than the other in the series and parallel circuit?
28. ### Need help understanding potential difference practically

I have a problem understanding the concept of potential difference. I get the picture of seeing it as a height difference for example (rock or water that would fall down) but what confuses me is that many times the order of elements in a circuit does not matter. To explain myself better: if I...
29. ### Ohm's law

According to Ohm's law, "Physical conditions remaining the same, the electric current flowing through a conductor is directly proportional to the potential difference across the two ends of the conductor" I have two conceptual queries: FIRST When the ends of the conductor are not connected to...
30. ### Oscillating Electron Beam potential between metal plates

Take the case where the electron-beam is oscillating between two parallel metal plates, there will be alternating potential developed between the plates as metal tries to negate all external electric fields. My query is, (1) How to calculate the potential developed and possible way to simulate...
31. ### Equivalent capacitance of a system from potential difference

Homework Statement Calculate the equivalent capacity of the capacitor system between points ##x## and ##y## Homework Equations ##C=q/V## The Attempt at a Solution I'm asking about this problem because I know how to calculate ##V_x-V_y##, but I don't know how can I extract the equivalent...
32. ### Calculate the deflection sensitivity in mm per volt

Homework Statement Describe a method by which the charge / mass ratio e / m of the electron has been determined. Calculate the deflection sensitivity (deflection of spot in mm per volt potential difference) of a cathode ray tube from the following data: electrons are accelerated by a...
33. ### Calculate the speed of the electrons as they enter the gap

Homework Statement Two parallel metal sheets of length 10 cm are separated by 20 mm in a vacuum. A narrow beam of electrons enters symmetrically between them as shown. When a PD of 1000 V is applied between the plates the electron beam just misses one of the plates as it emerges. Calculate...
34. ### Find drift velocity of the current carriers in the copper strip

Homework Statement ABCD is a plane rectangular strip of conducting material of uniform thickness, with a steady current flowing uniformly from AD to BC. The potential difference between E and F, the mid-points respectively of AB and CD, is zero, but when a magnetic field is set up at right...
35. ### Potential difference of helium nucleus question

Homework Statement What potential difference is needed to give a helium nucleus (Q = 3.2 × 10-19 C) 50 keV of kinetic energy? Homework Equations V=U/Q 3.2 × 10-19 C = 2e The Attempt at a Solution I was quite sure I had the right answer but it keeps saying I'm wrong? V = (50*10^3 eV) / 2e =...
36. ### Contact potential difference

Homework Statement Hi! I'm writing my lab report on the Franck-Hertz experiment and I have trouble with the contact potential difference (inelastic collision). How do you calculate it? Homework Equations See below The Attempt at a Solution The energy differences between the maximum and...
37. ### Potential Difference Between Points on Dielectric Triangle

Homework Statement A dielectric equilateral triangle of dielectric constant 30 is inserted into uniform horizontal electric field of 100,000 N/C. What is the potential difference between two points 3 cm apart on one of the sides? Homework Equations ΔV =∫E⋅dl E' =E/κ The Attempt at a...
38. ### Radius and period of charge in B field

Homework Statement A doubly charged helium atom (mass = 6.68 x 10-27 kg) is accelerated through a potential difference of 4.00x 103 V. What will be the radius of curvature of the path of the atom if it is in a uniform 0.460 T magnetic field? Note: I hope this question is meant in advanced...
39. ### Conical Surface Potential Difference

Hey guys! The question is related to problem 2.26 from Electrodynamics by Griffiths (3ed). 1. Homework Statement A conical surface (an empty ice-cream cone) carries a uniform surface charge σ. The height of the cone is h, as the radius of the top. Find the potential difference between points a...
40. ### Capacitor Energy With Different Dielectrics

Homework Statement Two parallel plates are connected to a battery which maintains a constant potential difference of 12.0 V. The distance between the plates can be varied and there are three plates of different dielectric materials available: rubber (0.40 mm, κ = 6.7), glass (4 mm, κ = 7) and...
41. ### Work that must be done to charge a spherical shell

1. Calculate the work that must be done on charges brought from infinity to charge a spherical shell of radius R = 0.100 m to a total charge of Q = 125 μC. 2. V = k_e\int{\frac{dq}{r}} \triangle V = - \int{E \cdot ds} W = q\triangle V 3. I started with assuming the spherical shell produces...
42. ### How conductors/resistors affect electric fields?

Disclaimer: I'm not sure if this is the correct forum. An ideal conductor (ideal = no resistance) is essentially taking the electric field at one terminal and connecting it to the other terminal. Charge moves when it is in an electric field, electric field strength is in Volts per meter, or...
43. P

### How is electrical current delivered into houses?

How is the potential difference done? How do they make electrons move? Do they use electrical field using positive (to atract them) or negative charges (to repel them)? Do they use variables magnetic fields?
44. ### Circuit analysis -- Voltage question

hello, i have a question regarding the way we represent information on circuit diagrams. The first is to do with representing output voltages: is V out always simply representing the voltage of whatever lies between/trapped between those two horizontal lines? Also, i see a lot of diagrams...
45. ### What does it mean to say a battery is however many volts?

For instance, at a point 1 meter from a 1 nC charge the voltage (potential difference) from the formula V = Kq/r, is given as 9 volts, 9 J/C. So what does it then mean to call a battery 9V, 9 J/C? Is this a battery capable of taking a 1 C charge from infinity and pushing to within 1m of a 1 nC...
46. ### Potential difference of each resistor

Homework Statement What is the potential difference across each resistor? I know that I'll have to incorporate the V=iR equation but I don't know where to start though... My first attempt was with these: R1=4 R2=8 R3=5 R4=6 R5=3 24-I1R1-I1R2-I3R3+I4R4+I5R5=0 but this lead me nowhere so I...
47. ### What happens when we connect 2 batteries + with +, - with -?

Homework Statement Batteries are connected together with their + and - poles. Homework Equations The Attempt at a Solution I quess that nothing happens because there is no change in potential difference.
48. ### Maximum Current Intensity

Homework Statement How can I get the maximum Current Intensity by connecting 72 cells to a 3 Ohm resistor each cell has a potential difference of 1.5 Volt and internal resistance of 1 Ohm Please don't tell me to connect them all in parallel or all in series as in parallel the potential...
49. ### Circuit Components-Potential differencd across LDR (photoresistor)

Homework Statement The following figure shows a potential divider circuit made up of a LDR and a variable resistor R. It is used to activate a buzzer circuit which sounds only at 2.6V and above. The resistance of the variable resistor varies from 100ohm to 10kohm while the resistance of the LDR...
50. ### A 60W lamp and a 120W lamp

A 60W lamp and a 120W lamp each have a potential difference of 120V across their terminals. a) What is the current through each lamp? I think you use the formula I = P/V and so: Lamp #1 = I = 60/120 and Lamp #2 = I = 120/120 But I don't know if that is right? Thank you so much for the help!