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Homework Help: Forward/Reverse Bias

  1. Apr 1, 2010 #1
    1. The problem statement, all variables and given/known data
    Which of the following circuits in the diagram provided would you use to measure the V-I characteristics of a:
    a. Forward biased diode i.e Vx>Vy? Explain.
    b. Reverse biased diode i.e Vx<Vy? Explain.

    2. Relevant equations
    None required I think.

    3. The attempt at a solution
    There is no working out I believe, just one of those theory type problems.

    Attached Files:

  2. jcsd
  3. Apr 1, 2010 #2
    If you have to choose between the two, then the 2 important points you need to consider in answering this are
    1. A voltmeter should have a very much higher resistance than the component it is placed across
    2. How does the resistance of a forward biased diode compare with the resistance of a reverse biased diode?
  4. Apr 1, 2010 #3
    okay well there's no resistance in a diode correct? there the voltmeter will have a higher resistance. In a reversed biased diode there is no current flowing thus also no resistance anywhere in the circuit right? whereas in a forward biased diode there will be a current thus resistance along its components.
  5. Apr 1, 2010 #4
    There is resistance: but the resistance of a diode depends on the direction of the applied pd.
    Why do you say that if no current flows there is no resistance?
    If you connect a battery across a component and no current flows through it, would you conclude that the component has no resistance or a very high resistance?
    There will be some resistance, but how does this compare with the resistance in reverse bias?
  6. Apr 1, 2010 #5
    Oh I see, so there would be a very high resistance in a reversed biased diode because no current would pass through it. Okay I understand that bit.
    And the resistance in a forward biased diode is far less than a reversed biased diode because current is actually passing through.
    Anyway getting back to the question, if the didoe is forward biased, then circuit 2 is the only one wherethe voltmeter would be greater than what it is placed across because it has the least resistance, and if it is reversed biased then voltmeter would be below the resistane of the diode. Is this correct? or is there more than I should look at?
  7. Apr 1, 2010 #6
    You are correct.
    In circuit 2 the voltmeter would be fine in that position for a forward biased diode. The V-meter will have a much greater resistance than the component it is placed across.
    Circuit 1 is better for the reverse bias diode.
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