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Homework Help: A question about electrons

  1. Apr 28, 2013 #1
    1. The problem statement, all variables and given/known data
    Hi,I am currently studying A-level physics in the UK.:smile:
    I have been taught that electrons in an atom are orbiting around the nucleus.
    I would like to ask a question:

    Consider 2 situations:
    A man is pushing a box forwards along a horizontal road.
    Work done = Fs
    The chemical energy of the man is converted into the kinetic energy of the box.
    In a closed circuit,chemical energy of the battery is converted to the kinetic energy of

    That means energy is related to force.Without energy,no force can be exerted on an object.
    In my case,if electrons are constantly moving around the nucleus,does it mean that the
    nucleus is exerting a force on the electron,so that the electrons have enough energy to
    move at any time instant?

    If that's true,consider (2) again,the chemical energy in batteries will eventually run out,so that
    there will be no more energy supplied to the circuit.
    Back to my original concern,once the nucleus has used up its energy,will the electron stop
    moving,and stick on the surface of the nucleus?

    Thx so much :s

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 28, 2013 #2
    I'll stick to the Bohr's model of the atom here as it makes sense easily. Now if a force is applied on a body, it is not necessary that work is done on it or energy is supplied. Work is defined as F.s or as Fscosθ where θ is the angle between the force and displacement vectors. So if the force is perpendicular to the movement of the object, no work is done on it.

    The nucleus of an atom does no work on the electron as it exerts a force perpendicular to the electron's displacement. The electrons are moving because they have energy of their own (kinetic energy).

    In case of the electric circuit, the electric field produced by the battery pushes the electrons. Here the battery does work because the force and displacement are parallel. And here the battery also gets exhausted as it uses up its chemical energy to produce a field and push the electrons.
  4. Apr 28, 2013 #3
    Then where does the energy of electron come from?Something must have exerted a force on it so that it can move,do you mean it has kinetic energy intrinsically?
  5. Apr 28, 2013 #4
    I guess the electron acquires its kinetic energy when it gets captured by the nucleus. Initially, say the electron was very far away ( you can say that it was in an orbit around the nucleus at infinite distance). Because of the attraction of the nucleus, it was brought into smaller and smaller orbits up to its current position. Here, you can see that the electron lost electrical potential energy and (by energy conservation) gained kinetic energy.
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