# Help

Discussion in 'General Electronics Chat' started by A.Simmons, Jun 24, 2013.

1. ### A.Simmons Thread Starter New Member

Jun 24, 2013
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I'm confused about where to start on this circuit. I know how to do the simple circuits but the complex circuits confuse me.

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2. ### WBahn Moderator

Mar 31, 2012
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Wouldn't it be nice to know what the value of R4 is? Why not start there?

You need to show your work so that we have a starting point to help you proceed. We won't do your work for you.

3. ### A.Simmons Thread Starter New Member

Jun 24, 2013
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How do you solve for R4, if I knew how to do this, I wouldn't ask yall

4. ### tshuck Well-Known Member

Oct 18, 2012
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Then you should explain what you do know, or what you think you might do. We aren't going to be doing your work for you...

...for starters, you have the current through an unknown resistor that has a known series resistance all across a known voltage.

Hint: Ohm's Law

Also, you needn't zip a docx... you can just post it as a png so people don't have to go through all that trouble to open your question...

5. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,166
775
Post the circuit then so we can all see it!!

6. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
So you post a circuit without showing any work saying that you don't know where to start. So I focus you in on one resistor and suggest that you start there. But then you won't show any attempt and say you don't know how to do it.

Just what is it you want? All indications right now are that you simply want someone else to work the problem for you so that you don't have to do anything but turn it in as your own work and claim the credit for it.

If you truly have no clue how to even make an attempt at starting the problem, then you are in the wrong course. Go back and retake the prerequisites or change to a less challenging major. Otherwise, take some responsibility for working YOUR homework and show some work.

7. ### A.Simmons Thread Starter New Member

Jun 24, 2013
5
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V=IR
10V=0.2(R)
R=50ohms
Is this correct?

Jun 24, 2013
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9. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Schematics are the language of electronics. If you need help posting a thumbnail we are willing to teach you, it is pretty much a necessary knowledge skill on forums like this.

How to upload an attachment.

To attach a document or picture to a post

Click "Go Advanced" at the bottom of your post,

One of several options will pop up,

Click "Manage Attachments" much further at the bottom of your post,

To upload a file from your computer click "Browse", then select the file.

Schematics should be .gif or .png format, pictures should be .jpg. .jpg formats will fuzz out schematics, and should not be used for that purpose.

---------------

If you want to display this file there is an old thread I made,

How to Display Attachments Full Size

10. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
Here is an image of the schematic that was on the doc that was in the zip in the first post.

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11. ### WBahn Moderator

Mar 31, 2012
18,093
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No. You are making a pretty common mistake. You are trying to throw an equation at a problem without understand what that equation means. So you see that you need an I and a V and so you grab the handiest I and V and crank away.

Ohm's Law, V=IR, relates the value of a resistor to the current through THAT resistor and the voltage across THAT resistance.

Is the 10V in the diagram the voltage across R4?

Q1) What is the effective resistance of the combination of R3 and R4?

Q2) What is the voltage across that effective resistance?

Q3) What is the current through that effective resistance?

Q4) What is the value of that effective resistance?

Q5) What is the value of R3?

Jun 24, 2013
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Thanks Bill