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capacitor and inductor

Discussion in 'Electronics Homework Help' started by bhuvanesh, Apr 20, 2014.

  1. bhuvanesh

    bhuvanesh

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    Aug 29, 2013
    voltage and why voltage cannot change instantaneously in capacitor but current but why current cannot change instantaneously in inductor.Thank you in advacne
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Perhaps you should tell us what you understand about these components.

    As a hint, what does a constant current do to a capacitor, and what does a constant voltage do to an inductor?
     
  3. duke37

    duke37

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    Jan 9, 2011
    Consider energy
     
  4. bhuvanesh

    bhuvanesh

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    Aug 29, 2013
    how current in capacitor changing instantaneously but not the voltage.
     
  5. Laplace

    Laplace

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    184
    Apr 4, 2010
    An inductor creates a magnetic field. A capacitor creates an electrostatic field. Energy is stored in the field. What causes the strength of the field to increase in each case?
     
  6. Ratch

    Ratch

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    Mar 10, 2013
    I don't understand the question. In the capacitor by itself, the rate of change in voltage is proportional to the current. If you want a spike of voltage across the cap, then you have to apply a step of current. Perhaps you can give an example of what you mean. Everything takes a finite amount of time to change. Instantaneous is theoretical.

    Ratch
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Did you mean to say impulse? (And that will only give you a step). No finite current is going to produce a spike in voltage across a theoretical capacitor. (Am I wrong?)
     
  8. Ratch

    Ratch

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    Mar 10, 2013
    If dE/dt = I/C , then no current means the voltage holds steady. A large fast step of current increases the voltage rapidly until the current drops back to zero. Then the cap voltage will hold at new larger value.

    Ratch
     
  9. Laplace

    Laplace

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    184
    Apr 4, 2010
    If I/C is a step that means that I/C goes from zero to some constant value instantaneously. That means that dE/dt goes from zero to some constant value. But a constant dE/dt means the voltage slope is a constant which is the same as saying that the voltage is a ramp. I don't believe that a voltage ramp can be called a spike.
     
  10. Ratch

    Ratch

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    Mar 10, 2013
    Nothing happens instantaneously in the real world. If a step voltage occurs in a capacitor, then a current spike occurs. When does a voltage stop being a ramp and start to be a step in the physical world?

    Ratch
     
  11. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    So which statement is correct?
     
  12. duke37

    duke37

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    Jan 9, 2011
    In #3 I suggested consider energy.
    If the capacitor is to be increased in voltage, it will need to be supplied with energy. To raise the voltage instantaneously it will need infinite power. This is not available here.
     
  13. Ratch

    Ratch

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    Mar 10, 2013
    The second statement. Sorry for the confusion.

    Ratch
     
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