Electronics > Beginners

How can this be? (picture)

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billbyrd1945:
To ebastler: No, I understand that R1 and R2 are in series within a parallel branch and therefore added together and then inverted (2 steps). Ditto for R3 and R4. And I intuitively know that R5 would be a series resistor outside the parallel branches. But how would I explain to my 12 year old granddaughter how to rule out R5 as a parallel circuit resistor? How would she know to use it's value rather than its inverse? Thank you

ebastler:

--- Quote from: billbyrd1945 on February 17, 2019, 12:52:59 pm ---To ebastler: No, I understand that R1 and R2 are in series within a parallel branch and therefore added together and then inverted (2 steps). Ditto for R3 and R4. And I intuitively know that R5 would be a series resistor outside the parallel branches. But how would I explain to my 12 year old granddaughter how to rule out R5 as a parallel circuit resistor? How would she know to use it's value rather than its inverse? Thank you

--- End quote ---

Well, all of the current that wants to flow from one battery terminal to the other needs to flow through R5. There is no alternative (parallel) path to R5 which the current could take. The current first has to find its way through the resistor network made of R1 to R4, and then (afterwards, sequentially, serially) flows though R5. So R5 is in series with the other resistor network.

Brumby:

--- Quote from: billbyrd1945 on February 17, 2019, 12:52:59 pm ---But how would I explain to my 12 year old granddaughter how to rule out R5 as a parallel circuit resistor? How would she know to use it's value rather than its inverse? Thank you

--- End quote ---

RE-DRAW THE CIRCUIT - in the 'conventional' format: Power rails at top and bottom - circuit in between, working left to right

eblaster has done this for you:

ebastler:
To add to my prior post:

I still like the "plumbing" analogy to explain such simple circuits. Think of your circuit as a system of water pipes. "Current" is the flow rate of the water passing through a pipe (gallons per minute, liters per second or whatever). "Voltage" is the water pressure you apply (e.g. via an elevated reservoir and a pump which brings the water back up to the reservoir).  "Resistors" are narrow sections of tubing which constrain the flow.

If your force the water to flow through two narrow sections in series, their resistances will add up -- for a given applied pressure, less water will flow through that circuit. If you provide two parallel paths to the water, the water can chose either way. You will get more water flow through those two paths combined than through each individual path. In other words, each parallel path can "conduct" water -- their conductivities (inverse resistances) add up.

billbyrd1945:
Okay. I'm thinking that a rule would be: When using conventional flow, the series resistor's output cannot be divided on its way back to the power source (or the next component). And such a resistor (or component having resistance) would be calculated in the analysis as a whole (non-inverted) value. In this case, the value would be 1000, not 1/1000.

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