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staticstical fluctuations

Discussion in 'Electronic Basics' started by PZ, Jan 12, 2006.

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  1. PZ

    PZ Guest


    " As the number of electrons N decreases, the statistical fluctualtions
    in the number becomes an increasing fraction of the total, limiting
    circuit performance and making circuit design more difficult.


    this doesn't prevent me from further reading, just wonder what
    statistical fluctualtions actually mean, in simple language.

  2. A basic example would be to measure the height of 100 people. You will get
    100 different values (assuming your method of measurement has enough

    A second example would be to measure the output voltage of 100 photo sensors
    that were illuminated with a constant source. Again, 100 different values
    are expected.

    A third example would be to collect data on the time before failure of 100
    light bulbs.

    Statistics are used to deal with data that are known to be subject to random
    fluctuations. Almost all data are, by the way.
  3. redbelly

    redbelly Guest

    Think of the current as a measure of how many electrons pass through a
    wire every second.

    But, this number is just an average. If you were to count the actual
    number of electrons every second, it would usually be different than
    the average number. These fluctuations from the average are what the
    person you are quoting is talking about.

  4. Rich Webb

    Rich Webb Guest

    The bigger your sample is, the closer your estimate of [something] is to
    the estimate that you would make with subsequent large samples.

    You're probably most accustomed to [something] being the average of some
    measurement of the sample, so consider an average weight. If you take
    the average weight of samples of, say, five people at a time then the
    results depend a lot on which five people you choose this time as
    opposed to next time, and your sample to sample variation will be large.

    If, on the other hand, you weight people in groups of 500 then you would
    intuitively expect that the average weights of successive groups would
    be closer to each other than the average weights of the groups with just
    five people each. (For this statistic, it turns out that the expected
    value of the spread of the average will scale by the square root of the
    number of samples but that's not really germane here.)

    So, turning it around, starting with mean weights determined by samples
    from large groups, the fluctuation in the results will be greater when
    the number of samples include in each group is reduced.
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