2 3 6 LIMITATIONS OF OHM S LAW Although Ohm s law has been found valid over a large class of materials there do exist materials

Question

2 3 6 LIMITATIONS OF OHM S LAW Although Ohm s law has been found valid over a large class of materials there do exist materials and devices used in electric circuits where the proportionality of V and I does not hold The deviations broadly are one or more of the following types a V ceases to be proportional to I Fig 3 5 b The relation between Vand I depends on the sign of V In other words if I is the current for a certain V then reversing the direction of V keeping its magnitude fixed does not produce a current of the same magnitude as I in the opposite direction Fig 3 6 This happens for example in a diode which we will study in Chapter 14 semiconductor 1 5 mA I LA 0 2 V Board Question FIGURE 3 6 Characteristic curve of a diode Note the different scales for negative and positive lues of the voltage and current Current I mA I FIGURE 3 5 The dashed line represents the linear Ohm s law The solid line is the voltage V versus current I for a good conductor IMP Negative Non linear resistance region region Voltage V V FIGURE 3 7 Variation of current versus voltage for GaAs

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