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Author Topic: How do I calculate the required electric field?  (Read 1278 times)

chiralSPO

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How do I calculate the required electric field?
« on: 05/09/2015 15:34:07 »
I have spent too long thinking about a problem and have gotten myself confused. Rather than spouting all the different ways I've gone about doing this calculation, I will just present the problem:

Imagine a flexible molecular chain that has a positively charged end (+1 electron unit, 1.62e–19 C) and one negatively charged end (–1 electron unit). For the sake of simplicity, let's say that the chain is neutral and non-polarizeable. If there is no applied external electric field, the chain will fold over to bring the charges as close together as possible, let's say 5Å (5e–10 m), but given an applied external field of sufficient strength, the chain will extend completely such that the charges are now separated by a distance of 15 Å. What is the minimum field strength required to accomplish this (for the moment assuming the solvent has no significant dielectric constant or polarizeability itself...)

Thank you!
« Last Edit: 05/09/2015 15:36:29 by chiralSPO »

evan_au

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Re: How do I calculate the required electric field?
« Reply #1 on: 06/09/2015 06:19:22 »
I am guessing that once you have separated the two ends, you can use a relatively low electric field to keep them separated.

But you are trying to work out the higher electric field needed to separate them when the two ends are initially adjacent?

This system exhibits hysteresis, so the solution will be multi-valued, depending on the initial state.

alancalverd

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Re: How do I calculate the required electric field?
« Reply #2 on: 06/09/2015 08:59:46 »
Force between two charges F = q1q2/4πε0r2

Work done to separate the charges E = ∫Fdr

Electric potential between the charges V = E/2q

∴ required field  =  V/r

It is left as an exercise to the reader......

chiralSPO

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Re: How do I calculate the required electric field?
« Reply #3 on: 07/09/2015 21:24:10 »
Thanks guys.

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Re: How do I calculate the required electric field?
« Reply #3 on: 07/09/2015 21:24:10 »