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Direction of electric field

  1. Jan 11, 2009 #1
    Why does the field's direction depend on the positive charge and the not negative? If there is a positive charge and a negative, the direction of the field is the positive force of attraction (towards the negative). The theory of convention always confused me because i thought it was the electrons that move and not the protons?
  2. jcsd
  3. Jan 11, 2009 #2
    It's just conventional. Why do you call left-side left? That's something people decide upon in the ancient days of language, and people since then stuck to it (for simplicity sake). The same idea can be apply to the direction of the force, someone (my first guess would be Faraday) defined the direction of the E field by its positive direction. If there it is a negative charge, just switch the E field, no big deal.

    Hope it helps (and I hope I understand the question properly)
  4. Jan 11, 2009 #3


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    Staff: Mentor

    You can blame Ben Franklin for your confusion. Before he became one of the USA's "Founding Fathers," he did some scientific investigation into electricity, specifically what we now know as "static electricity", with charged objects that attract and repel each other. He came up with the idea of an "electric fluid" that was normally distributed evenly. When you rubbed certain objects together, it transferred some of this fluid from one object to the other. One object now had an excess of electric fluid, which he called "positively charged." The other had a deficit of electric fluid, which he called "negatively charged." But he couldn't actually see which way the electric fluid flowed, so he had to guess, and designated one group of objects as "positive" and the others "negative."

    It turned out that Franklin's electric fluid was what we now know as a flow of electrons. But he guessed the flow direction wrong. By that time it was too late to get everybody to switch "positive" and "negative," so we're stuck with it!
  5. Jan 11, 2009 #4
    Hahaha, free history lesson there. (I guess my first guess was wrong, oh well).

    I guess want to note: which ever way the direction of the field is base on, the laws of physics is still the same. All your equations would just be a negative sign different. So don't worry too much about it.
  6. Jan 11, 2009 #5
    ah okay thanks. Sounds kind of lazy though. I always have to know why for things.
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