Electronics > Beginners
How can this be? (picture)
Rick Law:
--- Quote from: billbyrd1945 on February 14, 2019, 08:02:22 pm ---Thanks Rick! I actually think I understand everything you said. With regard to the misplaced red test point on R5, I think I actually got a negative value when measured but went ahead and recorded it as positive, so I knew I was probably confused about the polarity. Back to the drawing board.
--- End quote ---
Glad it helps - I had a few typos there but that apparently didn't hurt too much.
Re: that misplaced red-dot
Since you had the number you should (ie: that point is indeed below and not above R5), yeah, you did reverse the probe but that is no big deal. Now had that point really been above R5 and you got a non-zero number, that would be an error. If that number is big, it is telling you something and you should figure it out. That something is: either your meter is ill, or you can improve your technique, or your circuit is shorting out with something that it shouldn't be touching.
I have the habit of not applying enough pressure on the probe-tips. I am too concern that the probe may slip, touch something else and shorting things out.
When you see some off-the-wall reading like negative when you should see something else, you can use that kinds of opportunity to see if there is any way of improving your measurement techniques. (Or an excuse to get something nicer without feeling guilty).
Tom45:
--- Quote from: billbyrd1945 on February 14, 2019, 07:47:31 pm ---Here are the results measured as suggested. Now I will read the Rick Law response.
--- End quote ---
With the redrawn circuit it is easier to see what is happening. There are effectively 2 resistors in series:
R5 in series with ( (R3 + R4) in parallel with (R1 + R2) ). That is the voltage divider that I referred to earlier.
158.5 || 296.5 is 103.29 ohms.
The total resistance in the circuit is 1103.29 which means 0.00634 amps of current is flowing through R5 (7 volts / 0.00634 amps).
Part of that 0.0634 amps comes from the R3 + R4 branch, and the remainder comes from the R1 + R2 branch.
I have 45 in my user ID because I was born in 1945. Is that the case for you too?
Tom
billbyrd1945:
"I have 45 in my user ID because I was born in 1945. Is that the case for you too?"
That's a big Roger. December 7, 1945, and just now getting around to a lifelong desire to learn electronics. And I really appreciate all the help.
Tom45:
--- Quote from: billbyrd1945 on February 15, 2019, 12:52:16 am ---"I have 45 in my user ID because I was born in 1945. Is that the case for you too?"
That's a big Roger. December 7, 1945, and just now getting around to a lifelong desire to learn electronics. And I really appreciate all the help.
--- End quote ---
So, you are a youngster. I am a day older than you are. :-+
We are both too old to be baby boomers by a few weeks.
Tom
billbyrd1945:
Too Cool! ;D
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