Discussion in 'Homework Help' started by curban1590, Feb 9, 2016.

1. ### curban1590 Thread Starter New Member

Feb 9, 2016
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https://courseware.ee.calpoly.edu/~jzhang/EE112/Fall03/exam1.pdf
my problem is the same thing as question 1 on this sheet, the problem is my professor does not actually teach anything. He assumes we all know everything already and does no examples on the work he does which is my first class related to electrical engineering. I haven't seen any examples of questions and thus i had no idea what to do when he assigned this. Thank you for your help.

2. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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Do you know any first principles from which you can formulate an approach to the problem?

3. ### curban1590 Thread Starter New Member

Feb 9, 2016
6
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Ohms law, I=Q/t (I=Amperes,Q=Coulombs,t=time), V=W/Q (V=volts,W=joules,Q=coulombs) and thats pretty much it. I just do not know how to approach the problem.

4. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,675
2,720

You'll also need Joule's Law to help you with the first (unless you want to deal with transforming i,t, and R into V's and Q's!)

From there on, it's just calculus. Does that help?

FYI, the second part can be deduced by inspection...can you think of why?

5. ### curban1590 Thread Starter New Member

Feb 9, 2016
6
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Is it because it starts at 0 and ends at 0? Or because the total positive charge is equal to the total negative charge and they both cancel out? I'm sorry I have been teaching myself up to this point and i want to enjoy electrical engineering but i cant if i dont understand.

6. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,675
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One of these answers is correct, but it will be better for you to determine which. I told you the equations you need -- you just need to integrate through time.

7. ### #12 Expert

Nov 30, 2010
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(Cheat) What's the average current during the up slope of the first time interval?

8. ### curban1590 Thread Starter New Member

Feb 9, 2016
6
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I thought it would have something to do with slope, it is one from 0 to 1

9. ### WBahn Moderator

Mar 31, 2012
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And you don't have a text?

Most Circuits I courses have some kind of prereq such as Physics II (Intro to Electricity and Magnetism), but that's not universal. They almost all have a couple semesters of Calculus as prereqs. These are all problems that someone with those prereqs should be able to do on the first day of class, so the instructor may just be assuming that students paid attention during the prereq courses.

10. ### #12 Expert

Nov 30, 2010
16,257
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and you still can't tell what the average current is?

11. ### WBahn Moderator

Mar 31, 2012
17,715
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You should have been introduced (or at least it should be very easy to find in the early part of your text) that

$
i(t) \; = \; \frac{dq(t)}{dt}
$

If you integrate both sides, you get

$
q(t) \; = \; \int \, i(t) \, dt
$

You should be able to make a similar integral equations for the total energy by noting that power is the time-rate-change of energy and also that power is voltage times current. You know the current and you know the voltage via Ohm's Law.

So, take everything that you've been told, and show your best effort to solve the problem.

12. ### joeyd999 AAC Fanatic!

Jun 6, 2011
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Which part (a or b) of the question is this a cheat for?

13. ### curban1590 Thread Starter New Member

Feb 9, 2016
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There is a co requisite of pre calculus and that is it, but i have taken up to calc 2, i have not taken ANY physics yet and i definitely would have waited if I knew it would have helped me, but there was no way i could have known and if i drop now i lose all financial aid so im in a bind here. the text is:
INTRODUCTORY CIRCUIT ANALYSIS
but looking at it when he did not explain what section this would be in or anything has left me clueless.

14. ### #12 Expert

Nov 30, 2010
16,257
6,757
If neither you nor the student know, I give up.

15. ### curban1590 Thread Starter New Member

Feb 9, 2016
6
0
The total rate of change of the graph is 0, which should be reguarding the charge transferred in the second part right?

16. ### hp1729 Well-Known Member

Nov 23, 2015
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It looks like the handout needs to be supported by classroom stuff.

17. ### #12 Expert

Nov 30, 2010
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6,757
b) (The second part.) How much total charge is transferred in the same period of time?

Zero charge transferred? Do you mean all sine waves have no energy, so you can stick your finger in a light socket?
What is the point of this exercise of all the answers are zero?
What are the units of energy in this case?

18. ### WBahn Moderator

Mar 31, 2012
17,715
4,788
The total "rate" of change?

Or the total change?

There's a difference.

The second part of the question has a couple of reasonable interpretations. Show your work and explain your result and you should be okay regardless of which interpretation you choose.

19. ### WBahn Moderator

Mar 31, 2012
17,715
4,788
Zero charge transferred does not equate to zero energy transferred.

20. ### #12 Expert

Nov 30, 2010
16,257
6,757
Oh. In that case, all the answers are zero.