When do capacitors have the same charge

Capacitors C 1 and C 2 are in series. Their combination, labeled C S in the figure, is in parallel with C 3. Entering their values into the equation gives. This equivalent series capacitance is in parallel with the third capacitor; thus, the total is the sum. This technique of analyzing the combinations of capacitors piece by piece until a total is obtained can be applied to larger combinations of capacitors. Figure 4. A combination of series and parallel connections of capacitors.

Figure 5. Figure 6. A parallel connection always produces a greater capacitance, while here a smaller capacitance was assumed. This could happen only if the capacitors are connected in series.

Skip to main content. Electric Potential and Electric Field. Search for:. Capacitors in Series and Parallel Learning Objectives By the end of this section, you will be able to: Derive expressions for total capacitance in series and in parallel. Identify series and parallel parts in the combination of connection of capacitors. Calculate the effective capacitance in series and parallel given individual capacitances.

Example 1. This magnitude of electrical field is great enough to create an electrical spark in the air. Change the size of the plates and add a dielectric to see the effect on capacitance.

Change the voltage and see charges built up on the plates. Observe the electrical field in the capacitor. Measure the voltage and the electrical field. Does the capacitance of a device depend on the applied voltage? Does the capacitance of a device depend on the charge residing on it? Would you place the plates of a parallel-plate capacitor closer together or farther apart to increase their capacitance? The value of the capacitance is zero if the plates are not charged.

True or false? If the plates of a capacitor have different areas, will they acquire the same charge when the capacitor is connected across a battery? Does the capacitance of a spherical capacitor depend on which sphere is charged positively or negatively? What charge is stored in a capacitor when Calculate the voltage applied to a capacitor when it holds of charge. What voltage must be applied to an 8. What capacitance is needed to store of charge at a voltage of V?

The plates of an empty parallel-plate capacitor of capacitance 5. What is the area of each plate? What is the separation between its plates? A set of parallel plates has a capacitance of. How much charge must be added to the plates to increase the potential difference between them by V? Consider Earth to be a spherical conductor of radius km and calculate its capacitance. An empty parallel-plate capacitor has a capacitance of.

How much charge must leak off its plates before the voltage across them is reduced by V? Skip to content Capacitance. Learning Objectives By the end of this section, you will be able to: Explain the concepts of a capacitor and its capacitance Describe how to evaluate the capacitance of a system of conductors. Both capacitors shown here were initially uncharged before being connected to a battery.

They now have charges of and respectively on their plates. The charge separation in a capacitor shows that the charges remain on the surfaces of the capacitor plates. Electrical field lines in a parallel-plate capacitor begin with positive charges and end with negative charges. The magnitude of the electrical field in the space between the plates is in direct proportion to the amount of charge on the capacitor. These are some typical capacitors used in electronic devices.

Problem-Solving Strategy: Calculating Capacitance. Parallel-Plate Capacitor The parallel-plate capacitor Figure has two identical conducting plates, each having a surface area A , separated by a distance d.

In a parallel-plate capacitor with plates separated by a distance d , each plate has the same surface area A. Solution Entering the given values into Figure yields. Spherical Capacitor A spherical capacitor is another set of conductors whose capacitance can be easily determined Figure. A spherical capacitor consists of two concentric conducting spheres. Note that the charges on a conductor reside on its surface. Cylindrical Capacitor A cylindrical capacitor consists of two concentric, conducting cylinders Figure.

A cylindrical capacitor consists of two concentric, conducting cylinders. Here, the charge on the outer surface of the inner cylinder is positive indicated by and the charge on the inner surface of the outer cylinder is negative indicated by. Further, as described above by WhatRoughBeasWhatRoughBeast, make no assumption that the charge across the the capacitors are identicle i.

Allow by Kirchhoff's current law that the current in the series are identically given by I. Thus, according to the relation between the current and the flow of charge through time. In conclusion, for a network of capacitors in series, one can derive the well known equation for the effective capacitance without the need to state that the charge across each capacitance is equal.

Allow by Kirchhoff's current law that the current in the series circuit is equal everywhere in the series circuit. Thus, according to the relation between the current i. Sign up to join this community. The best answers are voted up and rise to the top.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why is charge the same on every capacitor in series? Ask Question. Asked 5 years, 11 months ago. Active 1 month ago. Viewed 19k times. Junior Junior 4 4 gold badges 21 21 silver badges 44 44 bronze badges.

Of course, I did not read every response with the care and attention to detail that I should have. Assuming that the cap charge polarities are unambiguous BTW, do you also think that physicists don't know how a voltage doubler power supply works? The original questioner was interested to know why the charge at point B and C have to be numerically equal, as quoted above. The only person who explicitly contradicted this equality as far as I recall was John Mallinckrodt. You for example merely modelled the oscillation which could precede the new steady-state, did you not?

The difficulty of erroneously assigning equal charge on connected plates of series caps. I may have mentioned recently that I do NOT subscribe to the orthodox I deliberately do not say "old-fashioned" view that there are "natural laws" that scientists discover; I find it much more productive to suppose that there are man-made models - any of which may be more or less suitable to any particular case.

This has the particular virtue that when physicists comfortably think they are dealing on a 'more fundamental' level, I can as easily see the flaws in their models as in any other man made elaboration. This was the crux of Carl's question, was it not? I am afraid that this was at the heart of my sadness. It was Cockroft and Walton who defined this arrangement for a voltage multiplier in the earliest accelerator experiments.

They were physicists as I recall. But I don't suppose their names are known to teachers hereabouts. On careful deliberation, I have deleted the putative reason I offered for this. I hope you will accept this as a tribute to your private coaching in how to prevent public shows of sniping. Frankly, I wouldn't be at all surprised to find that Carl, having landed a position as a professor of physics in a university physics department, knows how to solve simple introductory physics problems like the one you posed.

Again, no. Please take the time and have the courtesy to read his post in its entirety. Since the net charge on the connected plates was irrelevant to Carl's central question, he explicitly made the simplifying assumption that it was zero. Read his post. Very interesting. No, quite clearly it was not. Why on earth would you suppose such an absurdity? I guess I get a little exercised by remorseless public shows of nonsense.

At the risk of being accused of a public show of sniping I must mention that this is not correct. Although my post did mention some of the details that must occur for the charge re-equilibration process to proceed, the point of it was to show how and why the second law makes the system minimize its macroscopic electrostatic potential energy in equilibrium.

This was an explicit consideration of an extreme geometry case similar to that which John Mallinckrodt considered and to which Carl Mungan asked about. BTW, my explanatory framework has no difficulty let alone an "overwhelming difficulty in explaining the reasonable case of two caps of different C value, precharged to the same voltage.

I'll forgo any further public sniping here since John Mallinckrodt did such a fine job of it in his previous post. David Bowman Its early in the morning, so this is with some hesitancy, but hey, I've already embarrassed myself. David remarked, concerning the requirement that all field lines starting on plate A must terminate on plate B: "Notice that this requirement of no net excess electric flux external to each of the capacitors is equivalent to a requirement of a vanishing field in the region between plates B and C.

For ideal infinite parallel plate capacitors, they are precisely equivalent as David, quite quickly and correctly, mentioned in pointing out one of my errors.

And I presume that in most reasonable geometries not extreme geometries they will be very very close to being equivalent, as almost all field lines would be in the region between plate A and B. One more qualification is necessary, if one wants to be "practical.

This was implicitly stated in the first message leakage resistances R1 and R2 have no effect. The engineers know about the effect of leakages very well; their d. We discussed this issue three years ago under the subject "a myth about capacitors in series.