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Homework Help: Physics proton electric field questions

  1. Feb 5, 2010 #1
    I have multiple choice questions, but I only get one chance, so I want to make sure I answer correctly.

    1. A charged rod is brought near a suspended object, which is attracted to the rod. Can we conclude that the suspended object is charged? Explain.
    o Yes
    o No

    Yes, the suspended object is negatively charged.

    2. A proton moves in a region of constant electric field. Does it follow that the proton's velocity is parallel to the electric field?
    o Yes
    o No

    No, it moves in the opposite direction.

    Does it follow that the proton's acceleration is parallel to the electric field? Explain.
    o Yes
    o No

    I am not sure in this case.
    Last edited by a moderator: Nov 7, 2017
  2. jcsd
  3. Feb 5, 2010 #2


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    Gold Member

    You're right if the rod is positively charged.
    Okay, you might say it's anti-parallel I think. But isn't the convention of the E-field direction as being from positive to negative charge? Think about it.
    Plus, a proton could have been throw in the E-field and its motion wouldn't be a straight line, making the question hard to answer.

    It does not follow from the past question, but in a constant E field, the proton suffer a force in the direction of the E-field. Why? Check out the definition of E-field, it is related to the force. Then think about Newton's second law about how force and acceleration are related.
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