What is Electric: Definition and 1000 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. SianRR

    Motion in Electric and Magnetic Fields -- (Uni Level Dynamics)

    I've attached my attempt at a solution below, I thought integrating it would be the best way to go but I'm just getting so confused and could use some help. This isn't my first attempt at a solution either I've been working on this for just under two hours now.
  2. Decimal

    Spectral density of radiative electric field

    So I have to find an expression for ##\vec{A}(\omega)##, $$\vec{A}(\omega) = \frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty} \vec{A}(t)e^{i\omega t} dt.$$ This point is where my confusion comes up. In the answer sheet they integrate over the retarded time ##t_r##, so the integral is...
  3. H

    Electric field between two capacitor plates (proof)

    See attached image
  4. D

    Electric field involving 4 point charges in a rectangle

    I am stuck on the following question (Image attached of my work) appears to make sense until i try to take a limit as c--->0 because the result should be 0. Am i missing something, if so can't you point me in the right direction. Thank you
  5. B

    Electric Fields: calculate the resultant force

    Summary:: I try to find the resultant force on "q". I think I have to find the value of Q, but I'm not sure. I Know F1 = k|q * 2Q| / 3² and F2 = k|q * Q| / 2² Hi, this is my first post on this forum I hope I posted in the right section. I try to find the resultant force on "q". I think I...
  6. G

    Gauss-Theorem on a solid dielectric sphere

    The load system formed by the point load and the load distribution generates two regions in space corresponding to r<1m and r>1m, i.e. inside and outside the sphere. Given the symmetry of the distribution, by means of the Gaussian theorem we can find the modulus of the field at a distance r from...
  7. Z

    Find the electric field on the surface of a sphere using Coulomb's law

    Note that the solution is 5625 V/m in z direction which is found easier using Gauss' law, but I want to find the same result using Coulombs law for confirmation. Lets give the radius 0.04 the variable a = 0.04m. ##\rho## is the charge distribution distributed evenly on the surface of the...
  8. Saptarshi Sarkar

    Electric field inside a polarized dielectric sphere

    My attempt: I know from Gauss' law in dielectric ##\nabla .D = ρ_f## where ##D = ε_0E + P##, so as ##ρ_f = 0## (as there is no free charge in the sphere) => ##\nabla .D = 0## => ##ε_0\nabla .E = \nabla .P## from this I get ##E = \frac {-kr^2 \hat r} {ε_0}## But, I know that for a uniformly...
  9. chemisthypnos

    How much steam is produced in an electric arc furnace?

    Hello, everyone. Does anyone know how much steam is produced by an electric arc furnace in a set amount of time? I have not been able to find any information on this despite how much water is no doubt used to cool the electric arc furnace. Can anyone help?
  10. Another

    What happens when electric current is distributed in the material?

    When supplying electricity to the material. the shape of the material may or may not be square. This material may be This material may be moisture materials or solid materials that may conduct electricity. I would like to know the travel characteristics of electric currents and the potential...
  11. A

    How to Solve an Electric Circuit Like This?

    Can someone please tell me to find R of this electric circuit? Please tell me the step-by-step. I have many problems of electric circuit like this. If you show me one, perhaps I can solve the rest of them.
  12. S

    The electric field of a piecewise uniform 1D charge distribution

    This is not really homework, but I'm having trouble understanding it intuitively. I came across this when learning about the space charge layer of a diode. The solution I know simply uses the 1D form of Gauss's law: ##\vec{\nabla} \cdot \vec{E}## = ##\dfrac{\rho}{\epsilon_0}## becomes...
  13. Saptarshi Sarkar

    Calculating total charge when the electric field is given

    I first tried to use the Gauss' law equation E.A = q/ε0 to find the total charge enclosed. The answer came out to be q(enclosed) = 4πqε0e^(-4r). So for r approaching infinity, q(enclosed) approached 0. Next, I tried the equation ∇·E = ρ/ε0, calculated rho to be -4qε0e^(-4r)/r^2 and total...
  14. askcr9

    A slab? Infinite area? Electric field? Help please

    The first time I saw this question I had no idea how to do it (as you can see in the figure, I lost a lot of points :s) because I was confused on how to even approach it with area of the slab from all sides being infinity. Right? That's problematic, no? Today, I just tried the problem again for...
  15. Moara

    Electron moving inside a region of homogeneous electric field

    a) since the eletric field is perpendicular to the inicial velocity, the x component is constant, hence Vf.cos45=Vo. This gives Vf=0,6√2.C b) Ei=γi.Eo , γi=5/4 , Ef=γf.Eo , γf=5/(2√7) Finally, Ei+e.E.d=Ef. Apparently this is incorrect, why??
  16. N

    Relativistic motion of an electron in a uniform electric field

    dv/dt is the acceleration, so I thought I could find the acceleration from F = qE = ma = dp/dt. But this is a relativistic case, so the proper acceleration is a = F/mγ3, where v in the gamma is the v of the electron and F = eE. However, I'm not sure if this is correct, because the constant τ...
  17. E

    Electric current and resistance question

    Homework Statement:: problem solving You build a wire by combining an 8 inches copper wire with a 10 inches nichrome wire. If their combine resistance is 10 kΩ, find the cross section area of both wires. The nichrome wire has twice the area of the copper wire. Homework Equations:: I = V/R...
  18. Z

    Tesla cybertruck is it a good electric vehicle

    tesla cybertruck does promise a range of 250 to 500 miles and has 1 - 3 electric motors. Is this a good electric vehicle purely based on just its specs.
  19. Elder1994

    Find the electric dipole moment for a water molecule

    The equation that we saw in class is for a continuous charge distribution, I think that for this exercise I need to treat the system as a discrete charge distribution but I'm not sure. Also, I don't know how I can calculate the intensity of the electric field needed to move this charge.
  20. N

    Electric Field of a Point Charge

    [moderators note: moved from technical forum, so no template] Summary: I can't tell where the mistake in my process is. The computer keeps telling me I am wrong. The Question: What is the electric field at point 1 in the figure? Give your answer in component form.(Figure 1)Assume that a =...
  21. N

    Electric cars: What do you think?

    I have been thinking about electric cars from an engineering point of view. I came to the conclusion that they are not worth it, for a number of reasons I will list below. What do you guys think? 1) Energy to charge the batteries must come from somewhere. If the source of the energy is nuclear...
  22. BickySmalls

    What would happen to a charge that is placed in an Electric Field = 0?

    If a charge was placed inside an electric field, where the electric field was equal to zero, what effect would the charge have?
  23. Q

    Find the sum of all these electric currents

    First, I got rid of amperemeters with 0 values. These are 9. 11 and 12. Amperemeter 4 will show the maximum value of electric current as it is placed directly between E and F. But how to know its value? Will it be 18 mA? I doubt because 18 mA is not said to be the maximum value. All other...
  24. Z

    Evaluate the electric field for two slabs of charge

    Thus I assume that one slab has positive charge Q1 and the other slab has negative charge Q2 = -Q1 There are 4 cases for the electric field: 1. x <= -a 2. -a <= x <= 0 3. 0 <= x <= a 4. a <= x The general case: Charge Density ##\rho = \frac {Q} {V}## Flux of E ##\phi_e = \oint \vec E \cdot d...
  25. E

    Electric field in a spherical shell

    Hi, been a while since I last asked here something. I am restudying electrostatics right now, and I am facing difficulties in the following question: My attempt: I tried to use Gauss' law, what I got is the equation in the capture but that doesn't lead me anywhere as I am unable to find a...
  26. Z

    Find the electric field of a cylindrical charge

    I begin by calculating the flux to be the flux of the cylinders lateral surface, which equals E*2*pi*p*h (p is the radius) The other two surfaces have E ortogonal to dA, so their flux is 0. Using Gauss law together with the calculated flux above, I get Flux = Q/e Flux = E*2*pi*p*h Solve for E...
  27. Diracobama2181

    Rigid Rotator in an Electric Field

    Since E_i=0 for the ground state, and $$E_f=\frac{(\hbar)^2l(l+1)}{2I}$$, $$w_{fi}=\frac{E_f-E_i}{\hbar}=\frac{(\hbar)l(l+1)}{2I}$$. So, $$d_f(\infty)=\frac{i}{\hbar}\int_{-\infty}^{\infty}<f|E_od_z|0>e^{\frac{i\hbar l(l+1)t}{2I}+\frac{t}{\tau}}dt$$ My question is in regards to...
  28. J

    Finding electric potential at a point between 3 electrodes.

    Firstly, I am not a English speaker. So I apologize that I cannot use English well.. I got a), c), e) a) at 0.5cm, E = -q/(2e_0*A) - Q/(2e_0*A) + q/(2e_0*A) = -1.4*10^7 V/m c) at 1.5 cm, E = 0 (inside electrode) e) at 2.5cm, E = -q/(2e_0*A) + Q/(2e_0*A) + q/(2e_0*A) = 1.4*10^7 V/m And I am...
  29. bryanso

    Why is the Electric Field outside this wire not zero?

    Not a homework. Just self-studying electromagnetism. I am stuck at understanding the very beginning of the solution steps in this example: The E as given in the solution is the field away from a long straight line with charge Lambda. That's clearly not the current configuration. E should...
  30. Moara

    Flux of Electric Field through a cone

    Since there is no charge inside the cone, the total flux through its surface is zero, hence Ø(lateral surface)+∅(base surface)=0. But ∅(base surface)=E.πR².cosΩ, because electric Field is homogenous. But by the figure, Ω is just arctg(h/R). So Ø(lateral surface)=-E.π.R².R/√(R²+h²). This is not...
  31. Boltzman Oscillation

    Engineering How do I find the electric fields for this capacitor?

    the image is given here along with some numerical information: Now I know that the formula for the electric field in a capacitor is given as: $$E = \frac{V}{d}$$ which I can use to obtain the three following fomulas: $$E_1 = \frac{V_1}{d}$$ $$E_2 = \frac{V_2}{d}$$ $$E_3 = \frac{V_3}{d}$$ where...
  32. binbagsss

    A Hamiltonian background magnetic field, perturbed by electric field

    Hi I'm looking at Tong notes http://www.damtp.cam.ac.uk/user/tong/qhe/two.pdf deriving the Kubo Formula, section 2.2.3, page 54,I don't understand where the Hamiltonian comes from (eq 2.8). I tried a quick google but couldn't find anything. I'm not very familiar with EM Hamiltonians, any help/...
  33. Samanko

    Potential energy of an electric dipole

    This is a problem from a textbook, and I can't solve it. I know that the equation of Potential energy of electric dipole. Since the configuration is a little bit complicated. I'm confused applying which electric fields.
  34. L

    How to find the equivalent resistance of this electric circuit?

    Summary: How to find equivalent resistance of the electric circuit? I need to solve the following problem: Calculate equivalent resistance of the circuit (figure1), if all six resistances are the same: r1 = r2 = r3 = r4 = r5 = r6 = 100 Ohm. True answer: 66.6 Ohm. I tried to solve this...
  35. X

    SpaceX Supersonic electric propulsion systems for airliners

    Tesla+SpaceX= supersonic VTOL suborbital electric jet? “I have an idea for a vertical takeoff and landing supersonic jet.” — Elon Musk, every time the subject of electric planes comes up, to include almost never using the VTOL abbreviation for some reason that’s probably very unimportant. —...
  36. K

    What kind of an electric motor with a reducer is needed for this?

    Homework Statement: what kind of electric motor with reducer is needed? Homework Equations: what kind of electric motor with reducer is needed? what kind of electric motor with reducer is needed? speed 55mm/s <moved to EE forum>
  37. B

    Electric field of light emitted by atom, given the intensity

    For t < 0 , all I can think of is a qualatative " the field is zero because the intensitity is 0 when the burst of light hasn't been emitted yet " For t >= 0 , I've tried squaring the given E and that let's me say the amplitudes are proportional (with a cos^2 term in the mix) But I feel like...
  38. U

    The Angular Momentum of an Electric and Magnetic Charge

    Relevant Equations: Angular momentum density stored in an electromagnetic field: $$\vec{l}_{em} = \epsilon_0[\vec{r} \times (\vec{E} \times \vec{B})]$$ Electric field of an electric charge: $$\frac{q_e}{4\pi\epsilon_0}\frac{r - r'}{|r - r'|^3}$$ Magnetic field of a magnetic charge...
  39. D

    Find the electric field inside and outside of a spherical shell superposition

    Hi! I need help with this problem. I tried to solve it by saying that it would be the same as the field of a the spherical shell alone plus the field of a point charge -q at A or B. For the field of the spherical shell I got ##E_1=\frac{q}{a\pi\epsilon_0 R^2}=\frac{\sigma}{\epsilon_0}## and for...
  40. RRouse

    Electric Singing Saw - Spring Steel Alloy (Material Science)

    This is a fun one, sort of! I am working on a singing saw that can be amplified with a regular magnetic pick up, from an electric guitar. I made a blade from laser cut1095 blue tempered spring steel (0.042" thick). It sounded great, but after a few months of service, the blade cracked. What is a...
  41. adamaero

    Electric energy density in the dielectric of a coaxial cable

    V(ρ) = V_o*ln(ρ/0.0018)/ln(45/180) (Attached picture is where the unit vector of r is really ρ.) In cylindrical coordinates ∇V = ρ*dV/dρ + 0 + 0 ∇V =derivative[V_o*ln(ρ/0.0018)/1.386]dρ ∇V = V_o*0.0018/(1.386*ρ) E = V_o*0.0012987/ρ Work = 0.5∫∫∫εE•E dv Bounds: 0.0018 to 0.00045 m D = εE =...
  42. Jelsborg

    Electric field of a spherical conductor with a dipole in the center

    In a recent test we were asked to calculate the electric field outside a concentric spherical metal shell, in which a point dipole of magnitude p was placed in the center. Given values are the outer radius of the shell, R, The thickness of the shell, ##\Delta R## and the magnitude of the dipole...
  43. jisbon

    Electric forces between conducting rod and rail

    Alright, to start off: I'm not even sure how this works in the first place. What I do understand is that if they carry current in the opposite direction, using right-hand grip rule, the magnetic field between them will be the same (into the page). Hence using the left-hand rule, I can deduce...
  44. weilam06

    Work done by an electric motor to drive elevator

    https://www.physicsforums.com/attachments/250022 For the part (a), set the tension of the string that pulls the elevator be ##T_1## and the tension that pushes the counterweight be ##T_2##. Then we have the following equations: $$T_1−1200g=1200 \cdot 1.5$$ $$1000g−T_2=1000 \cdot (−1.5)$$ where...
  45. N

    What are the advantages of a solenoid motor over an electric motor?

    Can force produced by solenoid be converted to mechanical force and be more efficient than electric motor's force?
  46. jisbon

    Find the velocity of a point charge in a ring of electric field

    Okay, I am not even sure how to startr with this question. But here's my theory: First I will need to the electric field produced by the ring using the formula: ##E = k\frac{\lambda a}{(x^2+a^2)^{3/2}}## After finding out electric field produced by ring, am I supposed to find out the...
  47. D

    How to show that the electric field inside a spherical shell is zero?

    Hi! I need help with this problem. I tried to do it the way you can see in the picture. I then has this: ##dE_z=dE\cdot \cos\theta## thus ##dE_z=\frac{\sigma dA}{4\pi\epsilon_0}\cos\theta=\frac{\sigma 2\pi L^2\sin\theta d\theta}{4\pi\epsilon_0 L^2}\cos\theta##. Then I integrated and ended up...
  48. D

    How to calculate the electric field at a point on the axis of two rings

    Hi! I need help with this problem. I tried to solve it like this: First I calculated the electric field of each ring: Thus the electric field at a point that is at a distance z from the ring is ##E=\frac{Qz}{4\pi\epsilon_0(z^2+r^2)^{3/2}}##, Thuss for the upper ring, the electric field would be...
  49. D

    Electric Flux through a circle

    Hi! My main problem is that I don't understand what the problem is telling me. What does it mean that the surface is a flast disc bounded by the circle? Is the Gauss surface the disc? Does that mean that inside the circle in the figure, there is a disc? Can you give me some guidance on how to...
  50. Snarlie

    Force & Torque on Electric Dipole in Magnetic Field

    Would this also be correct? Or is there something wrong with it? I appreciate all your responses! Snarlie
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