Charge distribution fail -need help

144

02:00:38

The voltage (and hence the charge) is not getting distributed between the initially charged  capacitor (2uF) and the uncharged capacitor (8uF) ... The voltage should get distributed like 8V and 2V after flipping the switch but that's not happening why??

published 7 years ago

kiani

7 years ago

http://everycircuit.com/circuit/5509057678147584

shubhampaul

7 years ago

@kiani Inspite of the added resistors the voltage distribution is same as my circuit.

shubhampaul

7 years ago

@kiani yeah after I slowed down the simulation I could see 8V for a brief moment and then at steady state it goes back to 2V... Why? Shouldn't the steady state be one capacitor at 8V and one at 2V ?

kiani

7 years ago

If you sloe the sim to 1us/s and check the currents in both capacitors,,. , in the case of the 2uf, cause there is no resistor to limit yhe current. There is a spike of 1kA,, and the other capacitor after the swich is fliked is 50 A. I don't know if the EC sampling rate can cover such sharp huge edges,,

shubhampaul

7 years ago

Yeah probably EC can't handle it. Thanks for the response @kiani

ViolationMad

7 years ago

@shubhampaul why do you think that the voltages would be different?

ViolationMad

7 years ago

In this simple case the charge on the cap can be seen as Q=C*U. When initially connected there will be 10V over the 2uF cap. Q=20uC. When you flip the switch you add a parallel capacity but no more charge. U=Q/(C1+C2) so U= 20uC/2uF+8uF=2V. So you have your 2V and the resistor just affects the time constant tau in which the charge will equal over both caps.

shubhampaul

7 years ago

@ViolationMad I know how the distribution of charge takes place capacitors when the capacitors are in parallel but in this case they are not parallel right? They are in series with a resistor... Isn't it?

ViolationMad

7 years ago

Even with all my Christmas fantasie I can't find series caps in this circuit. The switch is between the two caps isn't it? The resistor is in series with one of the caps which changes the charging konstant tau... But the voltages will be the same with or without it.

ViolationMad

7 years ago

http://everycircuit.com/circuit/5038261750988800

shubhampaul

7 years ago

Yeah you are correct with this. I got a bit confused with the resistor.

shubhampaul

7 years ago

The wrong solution of a book made me think that the voltage will distribute. Thank you @ViolationMad and @kiani

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