What is Capacitor charge: Definition and 34 Discussions

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charge: positive and negative (commonly carried by protons and electrons respectively). Like charges repel each other and unlike charges attract each other. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects.
Electric charge is a conserved property; the net charge of an isolated system, the amount of positive charge minus the amount of negative charge, cannot change. Electric charge is carried by subatomic particles. In ordinary matter, negative charge is carried by electrons, and positive charge is carried by the protons in the nuclei of atoms. If there are more electrons than protons in a piece of matter, it will have a negative charge, if there are fewer it will have a positive charge, and if there are equal numbers it will be neutral. Charge is quantized; it comes in integer multiples of individual small units called the elementary charge, e, about 1.602×10−19 coulombs, which is the smallest charge which can exist freely (particles called quarks have smaller charges, multiples of 1/3e, but they are only found in combination, and always combine to form particles with integer charge). The proton has a charge of +e, and the electron has a charge of −e.
Electric charges produce electric fields. A moving charge also produces a magnetic field. The interaction of electric charges with an electromagnetic field (combination of electric and magnetic fields) is the source of the electromagnetic (or Lorentz) force, which is one of the four fundamental forces in physics. The study of photon-mediated interactions among charged particles is called quantum electrodynamics.The SI derived unit of electric charge is the coulomb (C) named after French physicist Charles-Augustin de Coulomb. In electrical engineering it is also common to use the ampere-hour (Ah). In physics and chemistry it is common to use the elementary charge (e as a unit). Chemistry also uses the Faraday constant as the charge on a mole of electrons. The lowercase symbol q often denotes charge.

View More On Wikipedia.org
  1. K

    Calculating electric charge from graph (capacitor)

    Apparently, we need to integrate the functions from 0 to the time when it is fully charged. However, I integrated in terms of t so the soultion (according to a graph programme) should be around 236 Vs but I don’t see how this could help me.
  2. Zahid Iftikhar

    Why does a capacitor charge to 63% of the applied voltage?

    Statement of problem is given in the summary. Mathematics proves time constant is calculated from the equation V= V0 exp t/RC I want to know if there is any physical explanation of this effect. Please guide me on this. Regards
  3. D

    Making Capacitance the subject of discharge equation

    Homework Statement I have to rearrange the equation V=lnVo -t/RC to calculate C. The gradient from graph = -1/RC Homework EquationsThe Attempt at a Solution I got R/C=ln(Vo-V)/t but the answer I get is wrong
  4. A

    Why is the electric field inside the dielectric cancelling?

    So, I was studying force between the plates of a capacitor when a dielectric is inserted. Here is my question https://ibb.co/cenvXk Shouldn't it be like this picture below https://ibb.co/kOUsCk So, why is my teacher saying that the electric field inside the dielectric cancelling. So, what...
  5. PhysKid45

    Capacitor Charge Density Calculation

    Homework Statement Two 10-cm-diameter metal disks separated by a 0.64-mm-thick piece of Pyrex glass are charged to a potential difference of 1100 V . What is the surface charge density on the disks? What is the surface charge density on the glass? Homework Equations C=(e_0A)/d C=Q/V charge...
  6. P

    Coilgun capacitor charging circuit questions

    I've been making coil guns out of a disposable camera's flash circuit recently, and when experimenting with the capacitors themselves I've come across some things I can't explain, so I hope someone else can. 1. SOLVED: My mistake (In order to make my experiments easier, in place of the...
  7. I

    Engineering Calculating net change of capacitor charge in a circuit

    Homework Statement This problem apparently has a simple solution if you are good with circuit theorems but no matter what i try or how i combine them, it's just impossible. Given a circuit on the picture, and circuit parameters E3=12V,R1=1kΩ,R2=30Ω,R3=150Ω,R6=200Ω, if it is known that current...
  8. D

    MHB Capacitor Charge: Plotting for Different Objects

    I can't really be too specific, but from what I remember, how do we plot a capacitors charge for different objects?
  9. O

    Calculating Capacitor Charge Time: 1000 uF, R Value

    Hello all, I was reading this post on calculating the capacitor charge time: https://www.physicsforums.com/showthread.php?t=145203. My problem is i have a capacitor (1000uF) and i want to determine its charge time but don't know the R value, is it something i chose arbitrarily or should it...
  10. M

    Capacitor Charge Flow: Examining Circuit Behavior in Multisim

    Can a capacitor be discharged/recharged by using only one plate? I have a theoretical circuit with a transformer winding and a capacitor in series , one end of the winding is at +12v, then the other is connected to the capacitor , and the capacitor other plate connected to ground , what would...
  11. J

    Capacitor charge in series and parallel circuit

    Homework Statement Three capacitors, with capacitances C1 = 4.0 μF, C2 = 3.0 μF, and C3 = 2.0 μF, are connected to a 12 -V voltage source, as shown in the figure. What is the charge on capacitor C2 ?Homework Equations Q=VC Q = charge V = voltage C = capacitance Ceq = equivalent...
  12. C

    Capacitor charge question

    If two capacitors are connected in parallel to a battery and then the battery is removed, what happens to the charge on each capacitor? Do they move from one capacitor to another till they are distributed equally or do they stay in place?
  13. W

    Capacitor charge in parallel RC circuit

    Homework Statement What is Q(∞), the charge on the capacitor after the switch has been closed for a very long time? a circuit, whose image is attached, has known values for the resistors : R1 = R2 = 72 Ω, R3 = 101 Ω and R4 = 79 Ω, is C = 56 μF, V = 24 V. Homework Equations kirchoff's laws...
  14. Z

    Engineering Capacitor charge time on DC RLC circuit

    Homework Statement Inductor, resistor and a capacitor is connected to a DC source in series. DC source is 220 V Capacitance is 10F Inductance 5H Resistor 22 ohm Vc(0) = 50V Question is asking for the charge time of the capacitor, when it gets charged fully and then it starts to act...
  15. C

    Engineering Electric Circuit Capacitor Charge question

    Homework Statement An RC circuit is given with a 1μF capacitor, a 25kΩ resistor and a 4μF capacitor, all in series. Initially, the 1μF capacitor has a voltage of 40V, while the 4μF capacitor has a voltage of 0V. The circuit, starting from the left and going clockwise is, 1μF (reverse...
  16. Femme_physics

    Calculate Capacitor Charge Time for DC Motor

    Homework Statement The following is a circuit to activate D.C. motor. The circuit contains a capacitor that charges and discharges, and a circuit to activate/disconnect the D.C. motor (which does not appear in the drawing). When pressing P1, the capacitor C is charged, and when it reaches 30...
  17. R

    Capacitor Charge within a time period

    Homework Statement This is one of my oscillator circuits, that I am trying to develop a simple formula to calculate RC for Oscillation Frequency, based on the fact the oscillation is done with the Capacitor charge changing from 1.1V to 1.68V back and forth, for a set of physical numbers. What...
  18. P

    Decreasing Capacitor charge time

    im working on a project that is using a parallel capacitor bank made of four 400V 6300uf caps. I am going to use a 120V outlet as the power source and my problem and question are this: as it is, according to pspice, it will take roughly forever for the bank to reach its 400V from the CW...
  19. J

    Solving an Electric Circuit: Potential Difference & Capacitor Charge

    Homework Statement I have this circuit here.. http://s1167.photobucket.com/albums/q639/jay9313/?action=view&current=EM.jpg The question says that when switch S is open in the circuit shown above, the potential difference between points a and b would be.. A) 0V B) 6V C) 12V D) 24V E) 36V...
  20. K

    Capacitor Charge Drain and Surge Impedance

    If I have a cable of 84 ohms of characteristic (or surge) impedance (which is independent of length) and whose DC resistance is far greater than 84 ohms (let's say 840 ohms), would I get, by hooking up a capacitor charged at 12 volts across it for a very short period of time (let's say 1...
  21. T

    Capacitor charge or discharge.

    Pls tell me why is it easier for a capacitor to discharge rather than charge.?
  22. B

    RRC Circuit - Capacitor Charge?

    Homework Statement http://www.webassign.net/hrw/hrw7_27-76.gif The circuit in the figure shows a capacitor, two ideal batteries, two resistors, and a switch S. Initially S has been open for a long time. If it is then closed for a long time, what is the charge (in Coulombs) on the capacitor...
  23. O

    Capacitor Charge Discharge Clarification

    Ok so i am just trying to clarify a few points about capacitor charge, discharge, i was wondering if anyone could help. 1)In charging, am i right in thinking current decreases exponentially, charge increases exponentially, and voltage increases exponentially.? 3) Am i write in thinking in...
  24. B

    Capacitive Keyboard: Calculating Effective Capacitance and Charge Transfer

    Homework Statement On one capacitative keyboard, each key has a capacitor bottom plate 7[mm]×7[mm] with a 0.4[mm] thick sheet of mica (κ≈7) on top of it; the capacitor top plate is the same size, glued to the key bottom, usually 4[mm] from the bottom plate ; the bottom plate is 5[V] higher...
  25. A

    Parallel-plate capacitor charge problem

    Homework Statement Two 10.0 -diameter electrodes 0.56 apart form a parallel-plate capacitor. The electrodes are attached by metal wires to the terminals of a 14 battery. After a long time, the capacitor is disconnected from the battery but is not discharged. a. What is the charge on each...
  26. M

    RC Circuit find capacitor charge

    Homework Statement The capacitor in an RC circuit (R = 130 \Omega, C = 40uF) is initially uncharged. 1) Find the charge on the capacitor in the circuit one time constant (tau = RC) after the circuit is connected to a 9.0- V battery. 2) Find the current in the circuit one time constant (\tau...
  27. N

    Capacitor Charge: Stored in Plates or On Top?

    this may seem stupid but i can't remember is the charge in a capacitor stored within the plates or on top of the plates?
  28. D

    Circuit Elements: Battery, Resistors & Capacitor Charge 195μs Post Switch Open

    Three resistors and a capacitor are in a circuit with a battery: R1 = 23 Ω R2 = 13 Ω R3 = 15 Ω C = 6.2 µF V = 17 V The switch has been closed for a long time. What will the charge be on the capacitor 195 μs after the switch is opened? picture...
  29. T

    Calculating Capacitor Charge & Voltage: A Problem

    Homework Statement The current shown below is applied to a 0.25uF capacitor. The initial voltage on the capacitor is zero. (a) Find the charge on the capacitor at t = 30us. (b) Find the voltage on the capacitor at t = 50us. (c) How much energy is stored in the capacitor by this current...
  30. S

    Calculating Charge on Capacitors in Series

    Homework Statement A circuit composed of 2 capacitors of .40MF and .50MF are connected in series to a 9V battery. Calculate the charge on each I just have a general question. I know that capacitors in series have the same charge. I found Q to be 2MC and I was wondering if 1.8MC is the charge...
  31. C

    Engineering RC Circuit capacitor charge Help

    [SOLVED] RC Circuit Help Homework Statement What is the potential of point a with respect to point b in the circuit shown when switch S is open? Which point, a or b is at a higher potential? b.) What is the potential (after a long time) of point a with respect to ground when switch S is...
  32. I

    Capacitor Charge Calculation: C1 and C2 in Series

    there are two parallel plate capacitors C1 and C2 connected in series across a battery of emf V with a switch S. The capacitor C1 has some initial charge q0 while C2 is uncharged. I have connected the positive terminal of battery (of emf V) to the positive plate of capacitor C1. Final charge on...
  33. A

    Capacitor charge - LRC series circuit

    In differential equations I was assigned a few circuit exercises. I'm having trouble understanding them, but I'm pretty sure that if can understand the first one then I can get the rest of them. The first exercise asks for time of capacitor charge and the others ask for things like capacitor...
  34. A

    Time Constant / Capacitor Charge Time

    I know that T = CR (time constant = capacitor rating times resistance) but I do not know how to calculate (theoretically) the time taken for the final ~36.8% of the capacitor to charge. The first language of the lecturer is not English. I, and others, can barely understand a word he says...