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Homework Help: Transistor gain problem

  1. Jul 20, 2012 #1
    1. The problem statement, all variables and given/known data

    If a transistor circuit is used to amplify a 2.5 mA signal to at least
    0.1 A, what must be the minimum gain of the transistor circuit?

    b. Assume the amplifier consists of a number of transistors in series,
    each with a gain of 10. How many transistors are needed in this circuit? (Hint: Two such transistors in series would provide a total gain
    of 10 × 10 = 100.)

    2. Relevant equations
    gain current = output current/imput current

    3. The attempt at a solution
    for the first question i got that the current gain should be 40,000 by dividing .1 by 2.5*10^-6. i am not sure if this is correct, but if it is then how is it possible to get to 40,000 by multypling tens?(for question b)
  2. jcsd
  3. Jul 20, 2012 #2


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    Gold Member

    How many ma are in an amp? How many in .1 amp?
  4. Jul 21, 2012 #3
    well 1 million in an amp and 100,000 in .1 amps, so is this the answer for question b? that would be 5 transistors of ten in a row.
    but dont i have to get the same answer (as a total amplification) as in question a?
  5. Jul 21, 2012 #4


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    Gold Member

    Ah, well now see ... THAT'S where your problem is the Greek letter mu is the symbol for micro. The "ma" means MILLIamp, not microamp.
  6. Aug 13, 2012 #5
    oh! i dont know why it changed to ma the original problem uses mu i still need help with the problem! haha
  7. Aug 13, 2012 #6


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    Science Advisor
    Homework Helper
    Gold Member

    The question says

    So a gain of 100,000 would also be acceptable.
  8. Aug 13, 2012 #7
    ah! got to read with more attention! thanks !
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