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I am doing a Chemistry Lab in which it is completely student run. In this experiment, I basically set out the same exact voltaic cell, and used varying lengths of salt bridges as my independent variable. The lengths different by a couple cm (12, 9.5, 5, 2). And what I observed was that the smaller the salt bridge, than the higher the voltage. I am not 100% sure that what I observed was accurate, but it corresponds to the data I have. Is this right? and if it is then why? I know that increasing the total amount of salt bridges has an effect, but this is just one salt bridge cut into various lengths. My lab is due soon, and I'd love for some help, thank you.

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    $\begingroup$ For the same current, bridge elyte composition and cross section, there is a bigger potential drop along longer bridges, with is subtracted from the external cell voltage under the load. $\endgroup$
    – Poutnik
    Commented Apr 6, 2022 at 17:25
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    $\begingroup$ Current is proportional to ion migration speed that is proportional to potential gradient, which mean value is equal to potential difference on the bridge divided by its length. Make your conclusion. $\endgroup$
    – Poutnik
    Commented Apr 6, 2022 at 17:30
  • $\begingroup$ It's not like I haven't been searching, but I think the idea is a little too niche. I'm getting a lot of information on the amount of salt bridges on effect of voltage, and sure I can make an assumption, but I want to be 100% correct. I want to know why. It's interesting me to the point that its annoying that I don't understand, i've been searching for the past week, and this was kind of a last ditch effort kind of thing. I'm sorry that I have plagued this website with such a plebian question, like genuinely, if its common knowledge, then i will do more research. Thank you so much, sorry again $\endgroup$
    – Damian
    Commented Apr 6, 2022 at 17:43
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    $\begingroup$ One learns more from being wrong (when noticed) than from being right. The direct analogy is you need higher water pressure to push water through longer pipes for the same flow, what causes lower terminal pressure at the same initial pressure. $\endgroup$
    – Poutnik
    Commented Apr 6, 2022 at 17:55
  • $\begingroup$ You have your data, Presenting it and a more detailed description of your experimental technique would help. All you can do is present the data and technique and possibly repeat the experiment to see if it is repeatable. you observe a voltage variance. Is there a precise relationship with length? Have you measured the current? For some reason you thought the length of the salt bridge should have an effect. Why? You found that it did. Your job now is to verify the data, and define the conditions and possibly suggest experiments to explain the observations further. $\endgroup$
    – jimchmst
    Commented Apr 7, 2022 at 5:20

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If the cell is not delivering any current, the voltage does not depend on the length of the bridge. Let's call it $V_o$. It only depends on Nernst law. If the cell is working and delivers some current $I$, the measured voltage will decrease to $V$ < $V_o$, because of the internal resistance $R$ of the internal solution + bridge, with the following expression : ${V = V_o - RI}$. The internal resistance $R$ depends on a lot of parameters, like the nature and the concentration of the solutions, the distance between the electrodes, etc.

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  • $\begingroup$ Hi, I am getting a little confused here. If I am using an analog voltmeter to measure the voltage being created, does that means the cell is delivering or not delivering any current? Thank you! $\endgroup$
    – James
    Commented Feb 16, 2023 at 2:37
  • $\begingroup$ Using an analog voltmeter, the current delivered by the cell is so small, that it can be considered as zero. Its internal resistance $R$ is usually between 100 kilo ohms to 1 megohm. $\endgroup$
    – Maurice
    Commented Feb 16, 2023 at 10:13
  • $\begingroup$ Thank you for your answer. So if I am just making a Daniel cell and measuring the voltage created by the cell. It is considered not delivering some current and therefore the metal contact area will affect too much on the voltage we get, is it correct? Thank you! $\endgroup$
    – James
    Commented Feb 16, 2023 at 14:06
  • $\begingroup$ I don't know exactly what you mean when you speak about the "metal contact area" . Anyway, this area does not affect the voltage measured by the voltmeter on a Daniel cell. $\endgroup$
    – Maurice
    Commented Feb 16, 2023 at 16:32

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