Electricity Definition and 338 Discussions

Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.
The presence of an electric charge, which can be either positive or negative, produces an electric field. The movement of electric charges is an electric current and produces a magnetic field.
When a charge is placed in a location with a non-zero electric field, a force will act on it. The magnitude of this force is given by Coulomb's law. If the charge moves, the electric field would be doing work on the electric charge. Thus we can speak of electric potential at a certain point in space, which is equal to the work done by an external agent in carrying a unit of positive charge from an arbitrarily chosen reference point to that point without any acceleration and is typically measured in volts.
Electricity is at the heart of many modern technologies, being used for:

Electric power where electric current is used to energise equipment;
Electronics which deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.Electrical phenomena have been studied since antiquity, though progress in theoretical understanding remained slow until the seventeenth and eighteenth centuries. The theory of electromagnetism was developed in the 19th century, and by the end of that century electricity was being put to industrial and residential use by electrical engineers. The rapid expansion in electrical technology at this time transformed industry and society, becoming a driving force for the Second Industrial Revolution. Electricity's extraordinary versatility means it can be put to an almost limitless set of applications which include transport, heating, lighting, communications, and computation. Electrical power is now the backbone of modern industrial society.

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  1. kma

    I What happens to resistance of tap water as voltage is increased?

    1 In recent days I have done a few experiments measuring the current of water as it goes up from 9 volts up to 36 volts, and following Ohms law to convert it to resistance. And I discovered a very interesting trend. In between 9 and 18 volts, there is a massive drop in resistance (by around a...
  2. A

    I History behind Ohm's law

    Voltage SI unit = Volts Current SI unit = Ampere Resistance SI unit = Ohm Ohm's law : V=IR Did Georg Ohm (German), Ampere (French) & Volta (Italian) collaborated when Ohm came out with this electricity equation with units for voltage, current & resistance as per their surnames? Credit goes to...
  3. Shan43

    B How to find the current density in an alkaline electrolyzer?

    To my understanding, current density is simply the current flowing through the alkaline electrolyzer divided by the area (the units for current density are A/m^2). But what would the area be in this situation? Is it the area of the electrodes or maybe the area of the electrolyte solution or...
  4. A

    Trajectory of an electron traveling near a current-carrying wire

    B equals 50*10^-7 T (at first instance) Fm equals 8*10^-20 N (at first instance) I know Fm is perpendicular to the velocity, and I know the estimation of the trajectory (somewhat similar to the curve y=lnx). Since I think vertical velocity will be constant, only changing the x component, I...
  5. E

    Finding a radius of a wire

    i really have tried all the formulas out there and can't seem to get a solid answer
  6. xpell

    I What are the most energetic lightning "superbolts" ever measured?

    Hi! I would be interested in properly referenced data about the most powerful / energetic lightning bolts on Earth to get a good idea about their maximum possible order of magnitude (maybe depending on location?) Both direct measurements or indirect but well-founded estimates (e.g. satellite...
  7. Viona

    B The resistance of an ohmic conductor

    I know that the resistance of an ohmic conductor increases with length because the electrons going through the conductor must undergo more collisions in a longer conductor. But why decreasing the cross-sectional area of the conductor also increases the resistance of a conductor?
  8. Istiak

    Find the electric field

    Solution attempt
  9. P

    Resistance of a Pentagon

    The question is to find the resistance between points A and F. I understand that the resistor between OC can be removed. From this point onwards, resistor OC has been removed. Let the far right point of the diagram, where i5 and i7 exit from, be B. Is it possible to detach the remaining...
  10. amizy9990

    2 * 10 ^ 20 charges move in a wire when we connect a 3.7 V battery. Ho

    W=Q*V 2*10^20 Q * 3,7 V= 7,4*10^20 ??
  11. amizy9990

    A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire

    A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire. What speed do the electrons move when there is 2 A current in the wire. t=q/t=3,20*10^3 C/ 2.0 A = 1,5*10^22 s v= 1m/1,5*10^3s= 6,6*10^-4 m/s
  12. P

    Stewart-Tolman Effect (Current caused by Acceleration of wires)

    Consider the inertial reference frame in which the positive ions forming the crystal lattice of some portion of a metallic ring are at rest. In this frame, an inertial force of mra exists. Consider the electrons in this portion of the metallic ring. The inertial force of mra is exerted on the...
  13. P

    Do charges always lie on the inner surface of capacitors?

    Parallel plates A, B are 5mm apart, with charges +1C and -1C respectively. Parallel plates C, D are 2mm apart, with charges +1C and -1C respectively. Capacitor CD is slid between capacitor AB. Find the potential difference between AB. The key idea to solving this problem is to suppose that +1C...
  14. P

    Difficult capacitance problem -- 3 long concentric metal cylinders

    A solution I found online claims that the effective capacitance between the middle and inner shell can be seen as: C (effective) = C1 + C2, where C1 is the capacitance between the inner and outermost shell, and C2 is the capacitance between the middle and outermost shell. Apparently C1 and C2...
  15. P

    Electrical energy stored by charged concentric spherical shells

    I thought up of this problem myself, so I do not have solutions. I would appreciate if you could correct my approach to solving this problem. Firstly, the charge induced on the inner surface of shell B is -q, and so the charge on the outer surface of shell B is Q+q. The energy stored can be...
  16. P

    Principle of superposition for charges/induced charges

    The key observation to solve the above problem is that the charge Q can be dragged out into a flat capacitor plate parallel to the 2 existing plates. Apparently, while the charge distribution on the 2 existing plates changes, the total charge induced on each plate remains the same, due to the...
  17. P

    Force needed to hold together a capacitor

    I have 2 methods, which give 2 different solutions: Let sigma = charge per unit area Let plate 1 be the left plate, plate 2 = right plate. Method 1: Because they are insulating, consider the electric field at 3 regions; region 1 to the left of plate 1, region 2 between the plates, and region 3...
  18. P

    Force on a charged sphere

    The force per unit area (Pressure) on a part of the sphere is given by F = (E outside + E inside)/2 * Q = 0.5 (kQ/R^2) * (Q/ 4piR^2) = (Q^2/ 32pi^2 e0 R^4). I understand the above line. The solution then says this pressure is exerted on the contact area between the 2 spheres, as given by...
  19. E

    Could you check this Li-ion charging circuit?

    Can secondary cell can be described in circuit simulator?? With other symbols like capacitor. Also I wonder if there's a program that provide secondary cell(like Li-ion battery). Please help me
  20. F

    Trying to better understand the physics of electrical earth ground

    I'm trying to better understand the physics of how Earth ground works. In circuit analysis and other electronic courses they usually present a conceptual picture like below where the Earth is viewed as a path that completes a circuit? In this conceptual view, the current travels on the...
  21. Kaushik

    Does potential drop when a charge flows through a wire w/ 0 resistance?

    Let us connect a battery of potential difference V to a wire. There is no resistance. Nothing! Now the battery creates some potential difference and the charges in the conducting wire move due to the Electric field created in the conductor by the battery. So, as the charge moves, its potential...
  22. Kaushik

    Intuition about electromotive force (EMF)

    My understanding of emf Let us consider 2 parallel plates with charges (opp. but equal in magnitude) stored on it. When we connect both the plates from the outer side, the electrons from the lower potential (i.e., negatively charged plate) moves to the higher potential (positively charged plate)...
  23. Nomadyb

    Capacitor question -- Circuit loop with a capacitor and a changing B-field through the loop

    a) the EMF of ℰ induced on The Wire, as a function of the speed 𝑣of the wire you can find it. b) flow induced in the wire𝑖, 𝐶, 𝐵, and are denominated in 𝑙 𝑎 (𝑎= the acceleration of the wire). c) find the magnetic force acting on the wire in𝐶,𝐵, 𝑙 and𝑎. d) 𝑎 acceleration, 𝑚, 𝑔, 𝑙, and are...
  24. DerbisEternal

    Two Charged Balls on Strings

    Given the total angles in the x direction, I set up this: (mg/cos(x))*sin(x)-Fe=0 then isolated for x: mgtan(x)=(kq^2)/(2*sin^2x) sin^2(x)*tan(x)=(kq^2)/(2mg) From here I am stuck. How do I go forward when x is contained in two different trig functions on the left?
  25. M

    How to calculate the efficiency of a switch mode power supply?

    I know how to calculate the power output and input by analyzing the current in put and output with multimeters and using the formula P=VI. But P_out is obviously incomparably smaller than P_in so the efficiency would suck this way. Is there a better way to do this??
  26. Kaushik

    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...
  27. Leo Liu

    Why Can We Consider a Conducting Sphere as a Point Charge When Finding Its Electric Field?

    This page claims that "[t]he electric field outside the sphere is given by: ##{E} = {{kQ} \over {r^2}}##, just like a point charge". I would like to know the reason we should treat the sphere as a point charge, even if the charges are uniformly distributed throughout the surface of the...
  28. Sokolov

    Maximum voltage that can be applied to DC circuit with resistors

    I see that ##V_{ac}=V_{ab}+V_{bc}##, with ##V_{ab}=I_1R_1=I_2R_2## and ##V_{bc}=I_3R_3##. However, I don't see how to express mathematically the maximum value of ##V_{ac}##. Could someone please help me with this task?
  29. M

    Inducing electric current in a wire (a comparison)

    Consider the following experiment: from a lacquered copper wire we cut off twenty to thirty pieces of about 10 cm. From them we form a bundle of parallel wires and connect the two ends with one more wire each. The other ends of these two wires are connected to a sensitive analog ammeter. We hold...
  30. C

    Electrical current question

    I assume that because there is a resistance, the polarity of the voltage must be the same as the charge flow, and thus the current, in order for energy to flow in the same direction. For instance, could I use the example of a light bulb (the resistor) plugged into AC lines; we know that if the...
  31. menniandscience

    Retarded and advanced potentials

    "of the two types of solutions which the Maxwell equations yield for the wave equation, the retarded and advanced potentials, only the retarded field seems to have a physical meaning," let's start please with basic (and detailed as possible for the knowledgeable layman! p.s-which equation is...
  32. hiddenname

    I What are the potential effects on electricity due to Earth's magnetic field reversal?

    What is/are the potential or theoretical effect on electricity due to reversal of planetary magnetic field? Would circuitry continue to function or would knowledge and understanding need re-evaluating as a result of a reversal of our magnetic field on planet Earth? Note: this is not a homework...
  33. O

    I Efficiency of computers vs. brains

    Hi, I’m an undergraduate student interested in cognitive processes. I’m about to ask a very interdisciplinary question, and so hopefully I can find a physicists that can take on the challenge. What is the fundamental reason behind why modern electronic computers (transistor computers) are...
  34. I

    Inserting a dielectric material between two plates of a capacitor

    1. new capacity: ##C = K\cdot C_{0}##. 2. initial potential energy: ##U_{i} = \frac 1 2 \cdot C_{0}V_{0}^2##. 3. final potential energy: ##U_{f} = \frac 1 2 \cdot KC_{0}V_{0}^2##. 4. total work done: ##W_{tot} =\Delta U = U_{f} - U_{i} = \frac 1 2 \cdot (K-1)C_{0}V_{0}^2 > 0##. 5. also total...
  35. D

    Joule heating effect - qualitative explanation

    Hi, I understand mathematically why using low resistance results in a greater heating effect. Could someone give an intuitive and microscopic picture of why the current contributes more to a greater power dissipation by the resistor rather than the resistance contribution to the power...
  36. Guidestone

    Request for historical background on the concept of voltage

    Hi all. I'll get to the point. I've been interested in electricity since I was in college. Concepts such as current and resistance seemed easy to grasp for me but voltage remains a little bit obscure. It's thanks to this forum (specially forum members Jim Hardy r.i.p and SophieCentaur, sorry if...
  37. C

    I RC charging - intuition behind equal dissipated energies?

    Assume that a resistor R charges a capacitor C, whose other terminal is connected to the ground. The charge at time t = 0 is assumed to be null and the supply voltage is equal to V. We have, as is well known, ##i = \frac{V}{R} e^{-\frac{t}{RC}}##. Integrating ##\frac{i^2}{R}## between t = 0 and...
  38. Dr-LucienSanchez

    Calculate the total resistance by integration using the conductivity equation

    (i) Dividing the rod into thicknesses of dx we get discs of area A with lengths=dx so using (****) we have the resistance of a typical disc (between point x' and x'+dx) as: (1) ##R(x'dx)=\frac{dx}{g(x)A}## (ii) Using (1) and (*) and the integrating from a to b of the entire rod we get...
  39. callie123

    Can constant electrical current heat water?

    Hi, I'm trying to make a realistic scene, in which water is kept under constant electrical charge. If the power is around 75 milliamps, and it's in a stream about twenty feet across by ten feet deep, would this affect water temperature? Thanks!
  40. Zeynaz

    LDR circuit electricity question

    So far what i figured out is that R2 and R3 are in parallel, R1 and LDR in parallel. And these two parallel circuits are parallel to each other ( tell me if I am wrong) The voltmeter has to read 0 but I am not sure how i can achieve that. Is there a rule where when the resistance of each side...
  41. A

    AC Electricity Generation and Transmission over a Single Wire?

    I'm a bit confused as to why can't you transmit AC current over a single wire. For instance, say you have an AC generator which induces potential difference at different points of the wire and thus, creating current. Downstream, the wire can be split and applied to a load. When the wire is...
  42. Skrphys

    Electricity: Is it a longitudinal wave?

    I am a high school teacher and we were discussing waves and electricity in class today. One of my students asked me if electricity is a longitudinal wave or not and I had no idea how to answer. So, I realize that electric fields are what drive electrons to move through conducting wires, but...
  43. callie123

    How easily can a high amperage electric fence be shorted out?

    Researching for a Scifi novel that depends heavily upon electricity...something I don't know much about! Any input would be appreciated! My situation: Somebody is trying to sneak through a high powered electric fence. Is it at all feasible to short out the fence somehow -- like, connecting it...
  44. F

    Engineering Help me finding the current in here please (Circuit analysis)

    Hi! I've been struggling with this. Original exercise here: Find the value of Iy when R=0. And the value of Vx when R is infinite. For the first part of the question I did this since R=0: I've tried to solve this circuit and I get that Iy and I5 are 0 A, and this can't be possible since Iy...
  45. A

    Electrical generation from used water in my home

    Hi everyone. I was just out in my back garden and was watching the water from someone's shower pour down the pipe and out into a drain. I was thinking if all of the used water from my house just goes down a drain then why not try make use of it. If the water system continues after use and takes...
  46. SaiTatter

    I need to calculate the equivalent resistance

    Homework Statement The circuit is the one in "Fig.4" I need to calculate equivalent resistance between A and B. This is what I've tried: I think that the first resistor is shorted by that wire connected between A and E. Their answer looks like this, in fig 2.2.1. I'm not sure if their...
  47. arturo

    Potential across a conducting sphere surrounded by an insulator

    Homework Statement A conducting sphere has a radius of 2.25 m and carries a positive surplus charge of 35.0 mC. A protective layer of barium titanate is applied to the surface of the sphere to make it safe for laboratory workers nearby. Safety considerations dictate that the potential...
  48. callie123

    Writing: Input Wanted Water and Electricity...

    I'm working on a Scifi novel, and trying to make it somewhat...scientific! Any advice is appreciated. Here's my question: I'd like to write about a situation where a body of water is purposefully kept under electric charge for years on end. This body of water would vary in size and depth, but...
  49. H

    Electric arc: How to calculate the required voltage for a light bow?

    <Moderator's note: Moved from a homework forum.> Calculate the required voltage to produce a electric arc between 2 iron nails (distance: 3cm). I´ve read in the internet that you need 1 kV per mm. But how can I calculate this value, that I need 1kV per 1mm?
  50. A

    B The Gain of the Inverting Amplifier and Virtual Earth...

    This is an inverting amplifier incorporating an ideal op-amp with infinite open loop gain. I have a simple question concerning the derivation of its gain (-R2/R1). The point I circled is at 0V (Virtual Earth) but then, if V+=V-, Shouldn't Vout=0 regardless of what R2 and R1 are?? What's wrong in...
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