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Homework Help: Why is alpha dc when calculated from beta dfifferent from alpha calculated from Ic&Ie

  1. Nov 10, 2012 #1
    i have been asked in my lab report to calculate alpha in a bjt common emmitter circuit using 2 different formulas and explain why one is misleading.

    β=Ic/Ib= 537.1*10^-6/6.743*10^-6≈85
    α= Ic/Ie=573.1*10^-6/566.357*^-6≈1.011
    α=β/β +1≈0.988
    i have worked out the two values of alpha where our beta is roughly 85 however im not sure why alpha when calculated from Ic/Ie is missleading.

    i have tried to search on the internet however i have found nothing yet and same with my lecture notes.
    any help is very much appreciated and i applogise if this is in the wrong section.
    Last edited: Nov 10, 2012
  2. jcsd
  3. Nov 10, 2012 #2


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    welcome to pf!

    hi zee! welcome to pf! :smile:
    it's asking why (Ic/Ib)/((Ic/Ib)+1) = Ic/(Ic + Ib) is not equal to Ic/Ie :wink:
  4. Nov 10, 2012 #3
    Re: why is alpha dc when calculated from beta dfifferent from alpha calculated from I

    hi thanks for the quick reply tiny-tim however in this case they are infact equal since ic+ib=ie but im still getting different values. i feel it is something to do with the capacitors or the configuration of the resistors that is causing a slight error but im not sure and im even less sure about why this is misleading
    Last edited: Nov 10, 2012
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