13.6.2 Ohmic Devices   

The resistance of a coil of copper wire is constant as long as its dimensions and temperature are kept constant. Similarly, a carbon film resistor is expected to present a fixed resistance when operated at low power (since its temperature is expected to be relatively constant).

Resistors which obey Ohm’s Law (V=IR) are said to be ohmic. Obviously, the I-V graphs for ohmic resistors are straight lines passing through the origin. So the lines themselves are the “wiper lines” I introduced in the earlier section. The lower the wiper line leans towards the V-axis, the higher the resistance. So {{R}_{1}}>{{R}_{2}}>{{R}_{3}}.

Most off-the-shelve resistors can be assumed to be ohmic as long as they are operated at low power. When operated at high power, their temperature may change significantly and their resistances may be affected.

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