I'm very confused. Can you show a schematic?
But if what you say "Ic=Ik+Ir" is true, then your equation is simply:
Vc=1/c*Integral(Ic dt)
But Ir is going to vary as the capacitor charges, right?
Hi Barry,
Absolutely. Here you go:
View attachment 144214
Correct.
I am certain it is piece of cake for someone who knows his or her mathematics.
But I just spent several hours without cracking it, which is why I now ask for help. Sad but true.
/c0x
This can be solved by either the node method, loop method or superposition method. Are you familiar with Laplace transforms?
Superposition is the easiest method for this specific circuit. The circuit implements 2 simple first order LPF for both sources, .This can be solved by either the node method, loop method or superposition method. Are you familiar with Laplace transforms?
Superposition is the easiest method for this specific circuit. The circuit implements 2 simple first order LPF for both sources, .
Here is your solution. Just apply superposition and see page 4: **broken link removed**
Hi CataM,
Sounds simple, but not so easy for me. Maybe I should go back to school.
Am I on the right track if I think that one way to go is:
* generating expressions for Ic in s domain for both sources separately,
* then add the expressions to get combined expression for Ic,
* reduce and
* finally do inverse Laplace to get a time domain expression?
/c0x
5V + 10k*100µA according to the source polarities in the post #3 schematicHow do you get 6V at t = infinity?
Ik=100 uA =0.1 mA; given.
Ir=5/10k =0.5 mA; calculated (valid at t=0)
Const current source has infinite impedance. Ir-Ik must flow through the capacitor. (t=0)
The capacitor charges exponentially to final potential of 4V with a time const of 10k * 10nF
How do you get 6V at t = infinity?
5V + 10k*100µA according to the source polarities in the post #3 schematic ...
I think the best way to do this problem is by node analysis
--- cut ---
Any questions?
Yes but it is to much time consuming.Hi CataM,
Sounds simple, but not so easy for me. Maybe I should go back to school.
Am I on the right track if I think that one way to go is:
* generating expressions for Ic in s domain for both sources separately,
* then add the expressions to get combined expression for Ic,
* reduce and
* finally do inverse Laplace to get a time domain expression?
No current exists through the capacitor. If it did, the capacitor would be defective. Charge accumulates on one plate and depletes on the other plate for a net charge gain/loss of zero. The capacitor separates the charges and thereby becomes energized. That means the capacitor stores energy, not charge.
Some I recognize, some is forgotten long time ago. Maybe some of it I never actually learned...
Capacitance is a proportional measure of the amount of energy a capacitor can store at a specified voltage. A 1 farad capacitor can store a half joule of energy at one volt.Capacitance is the amount of charge required to increase the potential by 1 unit.
The net charge of a capacitor is the same at 0,100 or 1000 volts, specifically zero. That is because when a voltage is applied across a capacitor, the same amount of charge that enters at one plate leaves from the opposite plate. The charge is separated and unbalanced between the plates, but the net charge change is still zero. This separation causes a electric field to form between the plates, which is where the energy is stored. Therefore, the capacitor is "charged" with energy, not charge. So you might as well say the capacitor is "energized". Energized means imbued with energy, and is completely unambiguous and correct.Charge must flow. The capacitor stores charge.
The energy is actually stored in the dielectric (it can be a vacuum) in the electric field.
Flow of charge is current.
The current through the dielectric is called "displacement current"- see for details: https://en.wikipedia.org/wiki/Displacement_current
Alternating current flows through a capacitor just like a resistor: except for the phase.
The net charge of a capacitor is the same at 0,100 or 1000 volts, specifically zero...
A conducting sphere of radius R has a charge Q and a surface potential of Q/(4*pi*epsilon0*R) and a capacitance of 4*pi*epsilon0*R.
Capacitance of earth is about 100 uF
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