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Velocity of electron at the end of a contraction

  1. Apr 20, 2017 #1
    1. The problem statement, all variables and given/known data:
    Velocity of an electron at point A1 is Vo where cross sectional area is A. The velocity of electron at the end of contraction at point B where cross sectional area is 2A is V1.Find correct option

    a)V1< V0
    b)V1= V0
    c)V1> V0
    I have attached a picture of the question as well.
    Please refer to it for the diagram.
    (Question 9) image.jpg

    2. Relevant equations: I failed to relate it with electrostatics

    3. The attempt at a solution:
    I feel the given information is insufficient to determine the answer.
    something about the charge of the cross sectional area or atleast something more should have been mentioned.

  2. jcsd
  3. Apr 20, 2017 #2


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    How are the current densities related between the two sections? What about the current itself?
  4. Apr 21, 2017 #3
    I dont know...I have not learned current electricity yet
  5. Apr 22, 2017 #4


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    OK, then let's talk about charge carriers. You have two conductors one narrower than the other. Electrons flow through them like water molecules in a pipe under pressure. You are at a fixed point on the narrow conductor and count how many electrons per second pass before you. Your friend does the same thing on the wide conductor. Answer these two questions and you will see what's going on.
    1. Who counts more electrons per second?
    2. Given your previous answer, who sees electrons move by more quickly?
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