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#3037982 - 06/23/10 03:30 PM Electricity Math Problem  
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Ltfransky Offline
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Ok, I need help. I have this problem and I need guidance to the solution. I've figured out that Total amps is 1, and the total resistance is 120 Ohms. But I'm having trouble with the individual voltage drops.


Last edited by Ltfransky; 06/23/10 03:31 PM.

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#3038128 - 06/23/10 06:52 PM Re: Electricity Math Problem [Re: Ltfransky]  
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if the total is 120 Ohm (did not check) then you have 35 Ohm from F to E and 120 - 35 = 85 Ohm from E to A

Your voltage drop from F to E would of course be 35V, F to D then 70V.

its a tiny bit more complicated further on but I hope this helps you to complete your homework

#3038149 - 06/23/10 07:30 PM Re: Electricity Math Problem [Re: hansundfranz]  
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The answer F-A and F-B is the same, as they are the same potential. Almost a trick question.

It helps if you simplify the schematic, by replacing the parallel resistors with a single resistor.

Simplify as much as you can, you can always go back to a schematic that sits between original and simplicity.

where the 1 amp divides, write the values down.

[EDIT] Oh yeah, make the schematic go in a straight line from A (top) to F (bottom) and only use 'sidetracks' when you have to, since the 'twists' and turns are just there to confuse.

Last edited by JAMF; 06/23/10 07:36 PM.
#3038258 - 06/23/10 09:45 PM Re: Electricity Math Problem [Re: JAMF]  
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Originally Posted By: JAMF


It helps if you simplify the schematic, by replacing the parallel resistors with a single resistor.

Simplify as much as you can, you can always go back to a schematic that sits between original and simplicity.





Here's how I was taught to simplify:

1. Do you see two or more resistors in series?
- If yes, combine and redraw.
- If no, go to question #2.

2. Do you see two or more resistors in parallel?
- If yes, combine and redraw.
- If no, go to question #1.

thumbsup


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#3038262 - 06/23/10 09:55 PM Re: Electricity Math Problem [Re: Ragman]  
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Originally Posted By: Ragman


thumbsup


Nice job on the schematics. Just an oopsie in the last one. smile wink

#3038292 - 06/23/10 11:27 PM Re: Electricity Math Problem [Re: JAMF]  
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Wouldn't the last one be 120 Ohms? I understood the simplifying part of the circuits.

But when I try to calculate the Amp split and the voltage drop at the first parallel section (A-C), I'm a little stumped.

I tried to calculate F-C by using V = (35+35+71.4 Ohms) x 1 Amp. This gives me a voltage drop of 141.4 volts. But that doesn't seem right to me since I only have 120V to start. Maybe the current needs to split, but I don't know.


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#3038352 - 06/24/10 12:58 AM Re: Electricity Math Problem [Re: Ltfransky]  
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Originally Posted By: JAMF
Originally Posted By: Ragman


thumbsup


Nice job on the schematics. Just an oopsie in the last one. smile wink


DOH! duh

It's fixed now. I just forgot to change the label after the last diagram change.




Originally Posted By: Ltfransky
Wouldn't the last one be 120 Ohms? I understood the simplifying part of the circuits.

But when I try to calculate the Amp split and the voltage drop at the first parallel section (A-C), I'm a little stumped.

I tried to calculate F-C by using V = (35+35+71.4 Ohms) x 1 Amp. This gives me a voltage drop of 141.4 volts. But that doesn't seem right to me since I only have 120V to start. Maybe the current needs to split, but I don't know.



Remember that you have that 100ohm resistor (R6) in parallel. Here's a diagram of how that voltage drop measures when the circuit simulation is run.



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#3038747 - 06/24/10 04:45 PM Re: Electricity Math Problem [Re: Ltfransky]  
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Originally Posted By: Ltfransky
I tried to calculate F-C by using V = (35+35+71.4 Ohms) x 1 Amp. This gives me a voltage drop of 141.4 volts. But that doesn't seem right to me since I only have 120V to start. Maybe the current needs to split, but I don't know.
Yeah, you're formula will be V = (35+35) x 1 Amp + (71.4 Ohms x "Nleft" Amp) You just need to determine the amount of Ampere that flows in the left arm.

#3085035 - 09/02/10 12:12 AM Re: Electricity Math Problem [Re: Ltfransky]  
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Ok. Here we go. Please tell me if I'm right.

F-E=35V
F-D=70V
F-C=105.7V
F-B=120V
F-A=120V
B-D=50V
D-E=35V
It=1 Amp


Please Heatware Me!

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#3085580 - 09/02/10 06:39 PM Re: Electricity Math Problem [Re: Ltfransky]  
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That's it.

#3085618 - 09/02/10 07:13 PM Re: Electricity Math Problem [Re: Ltfransky]  
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And this is why I went with mechanical engineering rather than electrical

v6,
boNes


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#3085639 - 09/02/10 07:42 PM Re: Electricity Math Problem [Re: Ltfransky]  
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JAMF Offline
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Oh, it's not that bad, Bones. Just formulas and rules one has to come to grips with, like in engineering. Amps, voltages, power, flux, capacitance, they all are not too hard to grasp. Transistors on the other hand, they'll trip you up.

#3085813 - 09/02/10 11:00 PM Re: Electricity Math Problem [Re: Ltfransky]  
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Ltfransky Offline
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Thanks guys. (And JAMF in particular)


Please Heatware Me!

Ours is not to reason why. Ours is to do or die.
Tennyson

I have slipped the surly bonds of earth
And danced the skies on laughter-silvered wings..
Gillespie Magee, RCAF
#3134520 - 11/10/10 06:24 PM Re: Electricity Math Problem [Re: Ltfransky]  
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Ltfransky Offline
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Yes! 89% on my Gas Technician 3 written exam!


Please Heatware Me!

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Gillespie Magee, RCAF
#3134551 - 11/10/10 06:54 PM Re: Electricity Math Problem [Re: Ltfransky]  
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Congrats! cheers biggrin


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