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What is energy and work in electricity?

  1. Jul 22, 2009 #1
    I read an article about voltage. It's says it's the energy drop (work) per unit of charge. In mechanics, work is a force applied over a distance. Energy is the amount of force you can apply over a distance.

    But what about in electricity? The definition of energy in mechanics doesn't seem to *click* with electricity.

    Basically, what is work and energy in the context of electrical circuits?
     
  2. jcsd
  3. Jul 22, 2009 #2

    Dale

    Staff: Mentor

    The definition of work is the same in electricity as anywhere else: f.d

    The definition of energy is the same also: the capacity to do work.
     
  4. Jul 22, 2009 #3
    But if electrons are doing work on a light bulb, what is really going on?
     
  5. Jul 22, 2009 #4

    Dale

    Staff: Mentor

    At an atomic level a force is applied to the electrons which gain a little KE, quickly collide with atoms in the filament, and convert the KE to thermal energy. When the filament gets hot enough it glows due to normal blackbody radiation.
     
  6. Jul 22, 2009 #5
    Thanks. Finally, I read another article stating that voltage is the amount of energy stored in an imbalance of charge. Is this correct? If so, what is this energy?
     
  7. Jul 22, 2009 #6

    russ_watters

    User Avatar

    Staff: Mentor

    Could you post a link to these articles, please? Because that isn't correct. Voltage is not energy, it is analogous to force.
     
  8. Jul 22, 2009 #7
  9. Jul 22, 2009 #8
    Absolutely not; voltage multiplied by the imbalance of charge is the energy available.
     
  10. Jul 22, 2009 #9

    russ_watters

    User Avatar

    Staff: Mentor

    From the second link:
    Boy, I guess I could be wrong, but that seems an awfully cumbersome way of looking at it. I guess that makes force an energy per unit distance...

    [edit] Oh wait, that's not exactly the same as what you said in the previous post. Phrak has it...
     
  11. Jul 23, 2009 #10
    It is combersome. Rather than the ususal W = E q d = V q, somehow user111_23 has been presented with things like V = W/q as a touch stone.
     
    Last edited: Jul 23, 2009
  12. Jul 23, 2009 #11
    So wait, if voltage (electric potential difference, that is) isn't W/q or [tex]\Delta[/tex]PE/q, then what is it? :confused:

    Maybe I should just stop caring about physics.
     
  13. Jul 23, 2009 #12
    But it is. W = q V, and V = W/q. You've just learned about voltage in a manner that gives pause. When the rest of us hear "voltage is energy over charge", we have to take a moment to re-arrange terms to decide if it's true. That was my point, above.

    And besides that, you left out a spatial displacement (where you asked about voltage = work per unit of charge) in your original question, and confused everybody from the start, as we tried to read between the lines.

    Any ways, it seems you've got it now and you can continue on, without forgetting all about physics :smile:.
     
    Last edited: Jul 23, 2009
  14. Jul 23, 2009 #13
    I have seen textbooks that start the chapter on electrical energy with V=W/q or something like it. For example Halliday's _Fundamentals of Physics_ begins with a picture of a battery across a resistor, the battery is labeled with a curly letter E for "emf", there's a color-highlighted box that says that the curly E is defined as the derivative dW/dQ, then there's a cartoon of a man lifting up bowling balls and putting them on a platform, where they roll down a chute, and the analogy to gravity is presented.
     
    Last edited: Jul 23, 2009
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