Would charged capacitors repelmalcolmst postedLet me give a hypothetical situation. Say you have two charged capacitors (of any voltage.. I'm assuming if this is true it would mostly be effective with voltages of 1000+V and large enough plates). By placing the negative plates of each capacitor next to each other, would the capacitors repel? I'm assuming they would because they would both have an excess of electrons, and the repulsive force between the two nearest plates would be stronger than the attractive force between the negative plate of one capacitor and the positive of the other. Is this correct? Thanks! additional---------------------- Thanks for your answer. However, I was just trying to do the math using Coulomb's law. Say all the plates are seperated by 1 unit. The repulsive plates would then be seperated by 1 unit (negative) and 3 units (positive) yielding: F = k q^2 / 1^2 and F = k q^2 / 3^2 in total F = 10 k q^2 / 9 The attracting plates would be seperated by 2 units for both of them yielding: F = -k q^2/2^2 and in total F = -k q^2 / 2 I can see the repulsive force would be quite small because it would be about half as great as it would be without the attracting plates. However if I am doing the math right, wouldn't it exist? Thanks! additional---------------------- (oh and I do realize "half as great" is probably very much an overestimate because in real life the capacitor plates would probably be very close together, not 1 meter as I have used in this example!) additional---------------------- Oh I did forget to take into account the attractive force between the positive and negative plates of both individual capacitors (I guess I assumed because those plates are fixed it won't matter). You are probably right! additional---------------------- OK I'm sorry for the confusion. Here's my updated math... if anyone sees a problem please let me know! Assuming: - the left capacitor (C1) is fixed - the right capacitor (C2) is movable but the plates are fixed - k * q^2 = n (for simplicity) - again all plates are seperated by 1 unit (the furthest + plates are seperated by 3 units) I believe the attractions/repulsions are then as follows: C2- (left plate of C2): to C2+: n to the right to C1-: n to the right to C1+: n/4 to the left net: 7n/4 to the right C2+ (right plate of C2): to C2-: n to the left to C1-: n/4 to the left to C1+: n/9 to the right net: 41n/36 to the left total: 63n/36 - 41n/36 = 22n/36 = 11n/18 to the right So it would still have a small amount of repulsion. Does this look correct? Thank you! Sponsored Link-------------------------- simplicitus repliedThe answer is the simple two flat plate capacitors will, in general, exert a force on each other, but whether it is repulsive or not depends on the geometry. When a capacitor has a charge, it means that one plate of the capacitor has more or fewer electron than the other plate; it says nothing about the charges on the capacitor with respect to other objects in the universe. Consider two identical parallel plate capacitors. Suppose you connected them in parallel, connected the common negative terminal to ground, and charged both capacitors to 1000 volts. Now disconnect the capacitors from each other and from the ground. Though each of the capacitors is now charged to 1000 volts, their negative plates have no extra charge (though their positive plates do). Thus there would be no force between their negative plates, but there would be forces between their positive plates. And yes, if you brought the two positive plates very close together, you would be able to measure the force. Similarly, you could set up a situation where both positive plates were at ground potential, but the negative plates had excess charge and the two negative plates would repel. For the case you are actually thinking of, where one plate gets extra charge while the other plate loses charge so the capacitor as a whole is neutral, you are dealing with an electric dipole situation. http://en.wikipedia.org/wiki/Dipole This occurs not only the situation you have set up, but also with "polar molecules" http://www.school-for-champions.com/chem... And yes, a dipole creates an electric field and responds to an electric field so two capacitors would indeed generate forces between them. Whether that would be attraction, repulsion, or just a torque (twisting force) depends on the geometry. On the other hand, most capacitors that people actually use are set up so that there is no dipole. For example, instead of the two parallel plates being flat, they may be formed into a cylinder. In this case the effective charge at the axis of the cylinder is 0. mike1942f repliedNo. Because the structure of capacitors overwhelms the effect between them and the overall charge is nil (inside vs outside)
But if you make a capacitor of thin foil sheets and hang them a short distance apart and apply an electronic charge, the charges will try to push the sheets apart. |
