Electric Definition and 1000 Threads

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. Y

    Why Does the Electric Field Component Ex Require a Negative Sign?

    hello i would like to understand to something. here is the drew now for my question: i was able to find Ey and here is my correct answer: when i try to find Ex i didnt understand something, i found the correct answer but i need to put minus before and i want to know why? here is my solution...
  2. H

    I Why is the electric field in y direction in a TE guided wave?

    Hi, I have a fairly simple question, but the answer is probably not as simple. I'm not sure to understand why in a guided wave (TE), the electric field is in the y direction. I know ##E_z = 0##, but why ##E_x = 0, B_y = 0##?
  3. M

    Copper Losses in an Electric Generator

    When I use Ohm's law and other related equations to calculate the heating losses in a generator I get the power output of the generator. I assume I'm using the equations wrong, and I was hoping that someone could help set me strait. I think what I would like to know is what determines the...
  4. M

    How do I incorporate electric fields into capacitors?

    I know that I’m supposed to use proportional reasoning, but where does electric field even fit in? For whatever equation, I know I’m supposed to see how increasing the voltage by either 2 and 4 volts related to electric field. If electric field is the same as “U”, then wouldn’t it be...
  5. Astronuc

    I Proton electric polarizability and structure (recent measurement)

    Measured proton electromagnetic structure deviates from theoretical predictions https://www.nature.com/articles/s41586-022-05248-1Meanwhile - https://www.jlab.org/human_resources/recruiting/ELECTRON-ION COLLIDER JOB OPPORTUNITIES
  6. N

    I Questions about a Conductor in an Electric Field

    Dear PF, I have a question regarding a conductor in electric filed. I have formulated my question in attached PDF file ... would please be so kind and advise me please... Thanks you in advance ...
  7. L

    Building an Electric Motorcycle from Scratch

    Basically what I need is to figure out what motors I need for a design I am wanting to make for an electric motorcycle. I know that I want it to go around 60-70 mph, 60 could be the max speed if need be, for the motors to be able to move 700 lbs (which is crazy but my idea is crazy so I need it...
  8. G

    Electric chain hoist: need help with control circuitry

    I have been given an electrical chain hoist to repair. The symptom is that it suddenly stopped working. I have checked the motor's windings and they each show similar DC resistance of 0.0018 ohms. I have attached the schematic (dunno why it was rotated 90 degrees during the upload). The hoist...
  9. guyvsdcsniper

    Determining Electric and Magnetic field given certain conditions

    I am unsure of my solutions and am looking for some guidance. a.)The real part of the wave in complex notation can be written as ##\widetilde{A} = A^{i\delta}##. Writing the Complex Wave equation, we have ##\vec E(t) = \widetilde{A}e^{(-kz-\Omega t)} \hat x##. Therefore the real part is ##\vec...
  10. T

    Electric Potential of a Sphere: A Puzzling Problem

    I can calculate the electric field strength at any point above the plane with Gauss' Law (##E = \frac{\eta}{\varepsilon_0}##) and so the electric potential at any point a perpendicular distance ##z## above the conducting plane (##V=−\frac{\eta}{\varepsilon_0}z##). But I'm having trouble taking...
  11. P

    Engineering Electric field in spherical shell - trying to understand the location

    Nevermind.
  12. H

    Why Does the Electric Field Sum Instead of Cancel with Opposite Charges?

    If there are two charges positive and negative and their electric field point in the same direction then the total electric field would be their sum of magnitudes. Why don't we consider the sign of the charges? For example, a parallel plate capacitor is inside the region where both the positive...
  13. kma

    Can wet hair cause an electric shock if it gets into outlet/power cord

    Hi I have a very random question I would like to ask. Say if someone just got out the shower and either plugged something into the wall, or plugged a high voltage power cord into a device. In the process of doing so a small clump or strand of their wet hair manages to get into the socket or the...
  14. S

    B Lorentz Transformation of Electric & Magnetic Fields Visualized

    I made a tool for calculating and visualizing how the electric and magnetic fields transform under a Lorentz boost. Thought I'd share it here, in case anyone finds it interesting. https://em-transforms.vercel.app/
  15. rwh2100

    B Gravitational acceleration and sub-atomic electric charge

    Wak a ball with a bat and the ball accelerates. Now under gravity, hold the ball out horizontally, let go and the ball accelerates ... without a wak. Given that gravity arises from curved space-time, I suggest further that the acceleration of the ball arises when sub-atomic particles (in the...
  16. ermia

    Electric field needed to tear a conducting sphere

    ..
  17. josephsanders

    I Tangential electric force at a surface

    Suppose you have an infinite plane of charge. If the surface charge density is uniform, would the tangential electric force always be zero, even if it is not a conductor nor static? My thought process for this is that if you look at each point charge and draw the electric field lines, then at...
  18. ermia

    Electric field of a part of a hemisphere

    I tried gauss law. And the fact that if alpha is less than pi/2 we can say that we have two parts with angle alpha and one other part which has a normal field at the center. But non of them helped me answer. The problem's solution says that we can use the fact that our section has longitudinal...
  19. raymondd

    Calculate velocity in a "simple electric train"

    How do you calculate the terminal velocity of the train moving in a coiled copper wire with two magnets attached to the polar ends? I have attached someone else's work I've found on the internet here and need help
  20. P

    I Defining the Forces from Magnetic Fields and Electric Fields

    We define Electric Field Intensity vector at a point as the force experienced by a unit positive charge kept at a point. Is it correct to define B vector similarly that is, is B vector the magnetic force acting on an unit magnetic north pole and is it correct to call B vector Magnetic Field...
  21. LarryS

    I EM Four-Potential and INDUCED Electric Fields

    Say we have a long solenoid with a current that is fluctuating in time. Then the changing magnetic flux in the solenoid will induce an electric field around the outside of the solenoid (Faraday's Law). This induced electric field is not conservative and therefore cannot have a corresponding...
  22. V

    I Induced electric fields and induced magnetic fields confusion

    So changing magnetic fields induce electric fields (Faraday's law when the magnetic field is changed by either moving the source or by changing the current in the source that's causing the magnetic field, ie. we're not moving the conductor where an emf is induced so there's no f=qvXB). Also...
  23. Ahmed1029

    I How do I find the Direction of an induced electric field?

    Faraday's law tell's you about the line intergal of the electric field, but you have to know the direction of the induced electric field first in order to properly apply it. How can I find its direction? Is it in the same direction as the induced current?
  24. warhammer

    B Direction of Electric Field & Field Due to a Dipole

    Hi all. I am stuck with a seemingly silly doubt all of a sudden. The direction of Electric Field is taken from Positive to Negative (because Field Lines originate from a Positive Charge and terminate at Negative Charge). We know that direction of Dipole Moment is from Negative Charge to a...
  25. Nugatory

    Reversible electric motor - what am I looking at?

    I have a reversible electric motor that operates an automatic skylight, vintage 1985. I'm trying to figure out how it is supposed to work, but I don't recognize the rectangular gray components that are secured to the motor case with a length of plastic zip-tie. What might they be and how would...
  26. P

    Calculating eletric potential using line integral of electric field

    So, I am able to calculate the electric potential in another way but I know that this way is supposed to work as well, but I don't get the correct result. I calculated the electric field at P in the previous exercise and its absolute value is $$ E = \frac {k Q} {D^2-0.25*l^2} $$ This is...
  27. mohammadmaaz789

    Understanding Dead Time Compensations in Electric Machine Drives

    https://i.stack.imgur.com/hSOU2.png https://i.stack.imgur.com/wE2Iy.png https://i.stack.imgur.com/R7FKK.png cannot understand this deadtime compensation method. So I have provided the whole cut out of the section of this book. BOOK: Control of Electric Machine Drive Systems Book by Seung-Ki...
  28. Javelin

    A Quantum Properties of Quasi Static Electric Fields

    Assume I could produce a stream of calcium ions from a 2nm diameter nanotube by pushing them through the nanotube using coulomb repulsion. Assuming these coulomb repulsed ions produce a stream of entangled ions which then create a slowly emitting quasi static electric (near) field. Even if...
  29. warhammer

    I Electric Field & Interplay between Coordinate Systems | DJ Griffiths

    Hi. I believe I have what may be both a silly and or a weird query. In many Griffiths Problems based on Electric Field I have seen that a coordinate system other than Cartesian is being used; then using Cartesian the symmetry of the problem is worked out to deduce that the field is in (say) z...
  30. T

    Misc. Looking for entry level DIY ideas

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  31. V

    I Electric field of a moving charge that's abruptly stopped

    Hello everyone, This is in reference to fig 5.19 (screen shot attached - please read the paragraph which says "Figure 5.19 shows the..."). I don't get why the field outside of the sphere of radius ct acts as though the particle would have continued its motion. Author's words : "The field...
  32. Salmone

    I How an induced electric dipole vibrates with EM field

    If we have an electromagnetic wave like the one in the picture and a molecule which is, in the image, the small black ball with electron cloud being the part with "minus sign" in it, does the molecule with its cloud start to oscillate, once the EM wave hits it, as an induced electric dipole...
  33. Tesla In Person

    Electric field strength at a point due to 3 charges

    I got E. 13q as the answer. That is what i did: The electric field due to +q at origin 0 should equal the electric fields of charges -3q and the new charge placed at 2x. So applying the equation above like this; k*(q) / (2^2) = -3q*k + (k*C)/ 4 solving for C the new charge added, gives 13q. I...
  34. Tesla In Person

    Flux of Electric field through sphere

    My attempt: We have 3 charges inside 2 +ve and 1 -ve so i just added them up. 4 + 5 +(-7) = 2q Then there is a -5q charge outside the sphere. I did 2q + (-5q)= -3q . The electric field flux formula is Flux= q/ E0 . So i got -3q/E0 which is obviously wrong : ) . After quick googling , I...
  35. Tesla In Person

    Electric Field Inside a Conducting Sphere: Is it Always Zero?

    Is the electric field inside a sphere always 0? Even if we have charges on the surface?
  36. N

    Electric Potential Field Calculation

    I've already tried to calculate the potential with respect to the 3 segments and then apply superposition (V1+V2+V3). However, I was not very successful. My error I think is in the calculation of the radii, mainly of the line segment that is on the z axis. Can anybody help me? I need some light...
  37. LCSphysicist

    The potential electric and vector potential of a moving charge

    I could try to apply the Liénard-WIechert equations immediatally, but i am not sure if i understand it appropriately, so i tried to find by myself, and would like to know if you agree with me. When the information arrives in ##P##, the particle will be at ##r##, such that this condition need to...
  38. Ahmed1029

    I How could electric susceptibilbility depend on position?

    In the statement encircled, what does Griffiths actually mean?
  39. M

    Charge density on the surface of a conductor

    I have tried to solve the problem by setting as a condition that the electric field inside the conductor has to be 0, but in this way I have two unknowns (σ1 and σ2):
  40. R

    Electric fan to get ramjet airborne?

    Does anyone know of prior work on the use of an electric fan to supply input air to a ramjet until the air speed is sufficient (~0.2 M) for normal operation? It's obviously possible, but might not be practical. The objective being the simplicity of a pulse jet without the vibration issues.
  41. HelloCthulhu

    How does an electric field create velocity in a water bridge?

    I've been researching water bridges and electrowetting to learn the effects of electric fields on water molecules but something continues to confuse me: if polar molecules can only rotate in an electric field, how is the water moving? Anyone familiar with this phenomenon? Any help is greatly...
  42. A

    Understanding Back EMF in Electric Motors

    Current drawn by motor = ##\frac{120-75}{90}## = 0.5 Amps The answer says the power output of the motor is 37.5 Watts. The only way I can get that answer is if P = IV = 0.5(75) = 37.5. This implies that in an electric motor, the back emf is the voltage of the motor. This confuses me because...
  43. A

    I Electric motor with increased load

    How come when the load is increased in an electric motor, the torque and current increase but the motor slows? Isn't how fast the motor is how much torque it has?
  44. 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##...
  45. link223

    Calculating the Electric field for a ring

    What i don't understand is why we are able to replace the ring with 'two oppositely charged superposed disks'? Just trying to understand.. So we have a uniform charge which means that this'll just be a simplification of the problem than, correct? Thanks in advance.
  46. A

    I Calculating Total Electric Charge with a Capacitor and Battery

    With a capacitor with a dielectric with the battery on, ##E_{total} = E_0 + E_i## ##\frac{Q_t}{dC_t} = \frac{Q_0}{dC_0} + \frac{Q_i}{dC_i}## thus, ##\frac{Q_t}{C_t} = \frac{Q_0}{C_0} + \frac{Q_i}{C_i}## since in a battery ##V_t = V_0, V_i = 0##, so either ##Q_i = 0## or ##C_i = infinite## but...
  47. MatinSAR

    Problem about electric potential

    Can anyone help me how to solve this problem ?! I am sure that my answer is not right :
  48. shivajikobardan

    The Potential of Electric Vehicle Energy Storage: Exploring V2G

    How can electric vehicle deliver energy to grid? This is the one of the few block diagrams that I could see in google. Do you have better one or can you explain this one? If I am not wrong. V2G is basically giving excess charge in your EV back to the grid.
  49. BnayaMeir

    Surface Current and Electric Field

    Hi everyone! I'm pretty new in this forum, I found the topics here very relevant to my physics course. And here is my question: Given the following drawing, two infinite sheets (in y and z axis) of ideal conductive material. their thickness is infinitesimal (dx->0). The electric field is...
  50. A

    Understanding Electric Field of Positive & Negative Plates

    I am confused with the solution. It says ##\vec E = \frac{\sigma}{\epsilon_0}##. Shouldn't E = ##2*\vec E = 2*\frac{\sigma}{\epsilon_0}##? Electric field of the positive plate and electric field of the negative plate.
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