# Capacitor bank

#### ahmedxwali

Joined Feb 2, 2023
2

It would be nice if someone could help me do these questions?

Also, doesn't the time constant for the voltage source and current source remain the same? Also, is the charge time constant and discharge time constant the same or different?

#### djsfantasi

Joined Apr 11, 2010
9,188
View attachment 286663

It would be nice if someone could help me do these questions?

Also, doesn't the time constant for the voltage source and current source remain the same? Also, is the charge time constant and discharge time constant the same or different?
First, is this school work ?

If so, it belongs in Homework Help (aka Homework Hints). Different rules apply to responding to school work.

#### MisterBill2

Joined Jan 23, 2018
19,461
My consulting fee for solving engineering problems is rather high. And this certainly is an engineering problem.
In fact, it looks a lot like an examination problem. And Ido not do exam problems, except on the board for everybody who took the test, after the test is taken and collected.

#### Papabravo

Joined Feb 24, 2006
21,314
If you look at the form of the differential equation for either the current or the voltage and you know something about the solutions to first order differential equations, the answer to your question should be manifestly obvious.

#### MisterBill2

Joined Jan 23, 2018
19,461
This looks like either an exam question or a homework assignment. I do not get involved with those.

#### WBahn

Joined Mar 31, 2012
30,303
It would be nice if someone could help me do these questions?
It would be even nicer if you would show YOUR best attempt to work YOUR homework, like you are supposed to.

Only then can we try to help you see what you are doing right, what you are doing wrong, and offer hints and suggestions on how you might move forward.

#### Halfpint786

Joined Feb 19, 2018
109
3.5 of the 5 replies above are crap (no offense), as is the case in every homework tread. Why have a homework thread if the first thing people do is tell the person "sorry, you are on your own"? The majority here assumes the only thing you can post is the answer. This thread is titled "Homework Help", not "Homework Answers", so stop pointing out that everything here is homework (they know that) and start helping them understand how to find the answers to their homework. Put your tutor hats on and say something more encouraging.

I'll start..
2.1 - finding the simplest equivalent circuit. You see how you have a series AND a parallel component to the circuit? To simplify that so there is only one resistor instead of two, you need to take the left side and find its parallel equivalent so that all 3 components are in parallel That allows you to then combine the parallel resistances to leave just one R and one C.

What I just wrote isn't the answer, i didn't even use a calculator, its teaching how to find the answer. How about everyone try that from now on instead of running off the people who need the most help!

#### djsfantasi

Joined Apr 11, 2010
9,188
3.5 of the 5 replies above are crap (no offense), as is the case in every homework tread. Why have a homework thread if the first thing people do is tell the person "sorry, you are on your own"?
Sorry you think those posts were “crap”.Did you read the sticky posts at the beginning of the sub-forum? They explain the unique rules of Homework Help. The way your original post was written appeared as if you were unfamiliar with these rules.

#### MisterBill2

Joined Jan 23, 2018
19,461
Aside from that, the range of questions presented is broad, really. When a student is needing assistance it is usually because some one problem is a stumper, or possibly 2 or three of them.
In this case we are given a whole sheet of questions with nothing indicating that the TS has tried at all to answer any of them. That is to say, no indication as to having put any effort into any attempt.
Mostly in my college experience the questions asked either in homework assignments or as exam questions were rather closely related to materials presented in class. The one exception was "Chemistry 2B "at LSUNO, where the exam questions were related to text material quite different from lecture material.
Of course, at many colleges, attending classes does provide a significant advantage towards doing well on examinations.

#### Halfpint786

Joined Feb 19, 2018
109
Aside from that, the range of questions presented is broad, really. When a student is needing assistance it is usually because some one problem is a stumper, or possibly 2 or three of them.
In this case we are given a whole sheet of questions with nothing indicating that the TS has tried at all to answer any of them. That is to say, no indication as to having put any effort into any attempt.
Mostly in my college experience the questions asked either in homework assignments or as exam questions were rather closely related to materials presented in class. The one exception was "Chemistry 2B "at LSUNO, where the exam questions were related to text material quite different from lecture material.
Of course, at many colleges, attending classes does provide a significant advantage towards doing well on examinations.
I can understand and respect that, sorry I blew up on the forum.

I guess I am speaking from the perspective of someone who didn't go to school for electronics, never had a teacher, no mentor or elmer in the hobby, just me, my books, my motivation, and the internet. Had I been turned away for not making an attempt, as valuable as that attempt may be, I would be half as far as I am now. Sometimes walking someone through a solution is what they need most, even if the question is changed so as to not give homework answers. I do not disagree with making people try their best, but this default "you better try yourself" can be discouraging in some cases and I think it should be approached differently. Just my opinion as someone who did horrible in school and sruggled a lot.

#### MisterBill2

Joined Jan 23, 2018
19,461
My guess is that if you became stumped on the first question that your request for help would be closer to " how do I determine which equation to use to solve for (whatever value is requested). instead of asking for help with a sheet of questions. After seven years of technical college I am aware of what the questions asked by those who are struggling look like. Been on both sides there.

#### Halfpint786

Joined Feb 19, 2018
109
Now that everyone has piled on top of me, I'll remind all of you that I never once suggested giving the answers. I was merely unaware that walking someone through how to solve a problem would be an immediate detriment to their education. I am glad I am in the midst of professional educators capable of correcting my error.

#### MisterBill2

Joined Jan 23, 2018
19,461
I tried to not "pile on", although I was a bit harsh with the TS. tarting with a blank page, as it were, is not the way to ask for answer to "what needs to be different here? It is really hard to see any error on a blank page is what it gets down to. Of course sometimes it is very challenging to see the actual error even when everything is written out clearly.

(Off topic ramble deleted)

#### dcbingaman

Joined Jun 30, 2021
1,065
A start to answering the first question that is 2.1 would be similar to this, can you perform this first?

#### MrAl

Joined Jun 17, 2014
11,725
View attachment 286663

It would be nice if someone could help me do these questions?

Also, doesn't the time constant for the voltage source and current source remain the same? Also, is the charge time constant and discharge time constant the same or different?
Hello,

When you ask if the time constant for a voltage source and current source remains the same, are you talking about a series RC circuit or parallel RC circuit or some other circuit like with just a capacitor?
To help a little, the response with a capacitor and voltage source is going to be much different than a capacitor and a current source. A current source assumes a particular current is flowing through a circuit loop all the time (barring a non conservative circuit), from start t=0 to finish whatever time that may be. A voltage source and capacitor usually implies an AC voltage source also.
The same for an RC series circuit. The response for voltage drive and current drive will be different. The current drive will force a current though the R and the C whereas with the voltage drive there will be a time constant.
For a parallel RC circuit, the current from a current source will split between the R and C but for the first instant it will all flow through the C. There will be a time constant there too.

You find out these things by analyzing the circuit using a general circuit analysis technique like Nodal Analysis. If you really really want to understand circuits like this (and many others) i have to strongly suggest first learning one or more general circuit analysis techniques. You can always ask questions about that here too.

I think maybe many people on forums dont remember what it was like before they learned how to analyze circuits. When i was first getting into it a very long time ago, i had no forum to work in and very few people to ask questions. It was back and forth to a less than adequate library for me on my bicycle. I had to ride several miles just to get to a somewhat more decent library. I also had to buy expensive books because no libraries close enough to me had any good ones and i wouldnt know what to ask for anyway.

Good luck.

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