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Current depends on what ?

  1. Apr 3, 2007 #1
    How do explain in plain English how current depends on ?
    I=Q/t
    I was told that it did not depend on time. I don't understand why it doesn't depend on time if the general formula as described previously consists of time.
     
  2. jcsd
  3. Apr 3, 2007 #2

    ZapperZ

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  4. Apr 3, 2007 #3
    In this equation:
    Q = electric charge passing a certain point in a given amount of time(measured in Coulombs)
    I = electric current passing that point (measured in Amps)

    As ZapperZ said:
    1 Amp = 1 Coulomb / 1 second

    So if 2 Coulombs of charge passes a certain point in 1 second there is 2 Amps of current flowing through that point.

    Sometimes the amount of current depends on time (in which case we say it is time dependent). Sometimes the amount of current does not depend on time (in which case we say it is time independent or we say it is not time dependent). It really just depends on the source of the current.

    If we say the current is not time dependent what we really mean is that if you measure the current at two different times then you'll get the same answer. The answer you get does not depend on what time it is when you measure it. For example: If you plug a lamp with a 60 Watt bulb into the wall and measure the current you'll get 0.5 Amps. I didn't tell you how I came up with 0.5 Amps. But my point is that if you measure it again in 10 hours (or two weeks), you'll still git 0.5 Amps. That's because the current coming into the lamp is constant over time. We have the power company to thank for this.

    If we say the current is time dependent (it DOES depend on time) what we mean is that if we measure it at two different times we will get two different answers. For example: If we hook up a small light bulb up to a battery and measure the current, we might measure 1.0 Amp. But if we measure it again in 10 hours, we might notice that the battery is starting to die. If the battery is starting to die then we will probably measure a current less than 1.0 Amps. If we come back in two weeks and measure the current, we will measure 0 Amps because the battery will have died.
     
  5. Apr 4, 2007 #4
    Does the current depend on alpha particles ? How ?
     
  6. Apr 4, 2007 #5

    berkeman

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    Nope. Why would you think that?
     
  7. Apr 4, 2007 #6
    Teacher asked me. I don't know the answer. He suggested me to think about it at home.
     
  8. Apr 4, 2007 #7

    berkeman

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    Well, the question is probably losing a lot in translation, but I'll just offer this. An alpha particle consists of what? What is the net charge of an alpha particle? And if an alpha particle is moving, based on the information that you were provided earlier in this thread, would you say that the alpha particle is contributing to a current of some kind?
     
  9. Apr 16, 2007 #8
    Nobody knows the answer.
     
  10. Apr 16, 2007 #9

    berkeman

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    Answer to what? The questions I posed in my post #7? Those questions were for you to answer -- they are easy to look up.
     
  11. Apr 16, 2007 #10

    Where should I look up ? I don't have the reference book.
     
  12. Apr 16, 2007 #11

    berkeman

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    Try wikipedia.org -- that's a reasonable starting point for introductdory subjects. Google is another source, but you need to add extra qualification words to your search there in order to narrow the results.

    What does wikipedia say about an alpha particle? What is its net charge? What does that tell you about the "current" from a stream of alpha particles?
     
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