Let\'s say I hook two capacitor in a parallel circuit with a voltage source. Wou
ID: 1375452 • Letter: L
Question
Let's say I hook two capacitor in a parallel circuit with a voltage source. Would the capacitor closer to the battery be charged up first? Because when the voltage excites and draws electrons from the plates, the electrons doesn't know where to go, so it goes through the first path it sees (i.e. the first capacitor) and it builds the plate of the first capacitor until it is done and then builds the next capacitor that follows?
Or would it start to build the first one first and then "evenly" builds charges on both capacitors because some of the electrons are actually getting repelled from the first plate of the first capacitor?
Explanation / Answer
A good analogy for an electrical circuit is to model it by a system of pipes with water flowing through them. The water represents the electrons and the voltage represents the pressure in the pipes. In this model the capacitors would be modelled by header tanks i.e. the pressure can pump water up into the tanks until the pressure from the height of the water in the tanks balances the pressure in the pipes.
When you connect the voltage source this is like turning on the water pump. When you do this the pressure wave from the pump propagates through the water at the speed of sound, so the pressure wave will reach the nearer header tank first. However the speed of the pressure wave is much faster than the motion of the water, so even though the pressure wave reaches the nearer tank first this is a very small time difference relative to the time taken to fill the tanks.
To get back to your circuit: when you connect the voltage source the "voltage wave" travels at a bit less than the speed of light so the nearer capacitor will start to charge first. However, assuming the difference in the length of the wires is a few cm, say 3cm to make the maths easier, the nearer capacitor will start charging 10?10 seconds before the farther one. The electrons actually move rather slowly, see http://en.wikipedia.org/wiki/Drift_velocity for details, so the time taken to charge the capacitors is likely to be far far longer than 10?10 seconds. The end result is that both capacitors will appear to charge simultaneously.
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