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About ohm law

  1. Oct 30, 2008 #1

    KFC

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    The ohm law for electricity is given by R = V/I

    Yesterday, my friend just took an experiment report to me which show the relation between R, V and I on a resistor and semiconductor separately. I saw that for resistor, R is almost a constant so V vs I is a straight line. However, for semiconductor, R is no longer a constant. My question is if I get a table to show a relation of V and I for a semiconductor, can I still apply R=V/I to calculate the resistance for difference I and V? What I am really confusing is in some textbook, it said the ohm law is R=V/I which gives a linear relation b/w V and I. So does it mean even I can use the same formular to calculate R but since it is no longer a linear relation, it is no longer the ohm law?
     
  2. jcsd
  3. Oct 31, 2008 #2
    Electrical resistance is notoriously non-linear, as the factors which define the resistance can actually change its value.

    Ohms law shows that as the applied voltage across the resistor increases, the resistance increases. Yet, if the applied current increases than the resistance decreases.
     
  4. Oct 31, 2008 #3
    What you are describing for the semi-conductor is called a load line, and shows the non-linearity between input voltage to output current and vice versa. It is this non-linearity which makes possible amplification and other effects such as modulation and oscillation. Ohm’s law is still applicable over short ranges of the load line, and the resistance at any point can be calculated either by calculus, or by drawing a tangent line to a point on the load line and calculating along the linear tangent line. The resistor can be considered as linear along the operating range of the resistor.
     
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