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A problem regarding the electric potential of an electron

  1. May 26, 2017 #1
    1. The problem statement, all variables and given/known data
    There is a sample problem in my physics textbook (Fundamentals of Physics, 10th Edition by David Halliday and others) which has some confusion in it for me. Please take a look at the snapshot I took, in the attachments.

    2. Relevant equations

    3. The attempt at a solution

    I do understand why the change in the electric potential energy of the electron is negative, because the electron tends to move upwards by its own to decrease its potential energy, right? But I don't understand why the textbook says the change in electric potential is positive and the electron moves to a higher potential? The electric field is pointed downward so naturally, the electron tends to move upward to decrease its potential energy. So at higher altitudes, the potential must be lower, not higher...?

    Also, how come there is such a big electric field of 150 N/C near earth's surface and thus tens of kilovolts in potential change?! How does it not affect our life or devices?

    And I think the textbook has a mistake in calculating the ∆V, it should be 75kV.
     

    Attached Files:

  2. jcsd
  3. May 26, 2017 #2

    scottdave

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    This video may help you to understand why you don't get messed up with electric fields in the atmosphere.
     
  4. May 26, 2017 #3

    haruspex

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    Don't confuse electric potential (aka voltage) with electric potential energy. When a charge q moves to a different potential (voltage) its change in potential energy is qΔV. If q is negative and it goes to a higher potential then that change will be negative.
     
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