Why semiconductors does not obey ohms law?

Answer 1

Tungsten is an example of a conductor that does not obey Ohm's Law. If you were to plot a graph of current against voltage, over a range of voltages, you will find that the result is a curve - showing that current is not directly proportional to voltage, which is the requirement for Ohm's Law.

While the ratio of voltage to current will indicate what the resistance happens to be for that particular ratio, you will find that, for tungsten, that ratio continually changes as you increase voltage - proving that tungsten does not obey Ohm's Law. The general rule is that if there is no straight-line relationship between voltage and current, then Ohm's Law doesn't apply.

The equation, R = V/R, does notrepresent Ohm's Law; it is derived from the definition of the ohm. Ohm's Law is a law of constant proportionality and constant proportionality only applies to linear conductors.

Answer 2

Ohm's Law always applies. In every case. That is why we call it a law. Its a matter of perspective.

Ohm's Law says that resistance is voltage divided by current. Nothing more. Nothing less. In particular, it does not say that the "resistor" has constant resistance.

At large currents, conductors get warm. Temperature changes their resistance. Ohm's Law still applies - you just need a new value of resistance.

Take an ordinary 40 watt light bulb. At operating power, it has a resistance of about 360 ohms. When cold, it has a resistance of about 27 ohms. Does it obey Ohm's Law? You bet it does - You just need to understand what the law says and what it does not say.

AnswerOhm's Law most definitely does NOT state that 'resistance is voltage divided by resistance'! It states, essentially, that the ratio of voltage to current must be constant for variations in voltage -which is not the same thing!

For Ohm's Law to apply, then, the ratio of voltage to current must remain constant for variations in voltage. So devices such as diodes, or conductors such as tungsten, do not obey Ohm's Law and are, for that reason, termed 'non-linear' or 'non-ohmic'. If you conducted an experiment using tungsten, for example, and plotted current against variations in voltage, the result would be a curve -confirming that tungsten does notobey Ohm's Law. In other words, Ohm's Law is NOT a universal law, and only applies to some materials or devices.

To answer your question directly if, as the current gets larger, the resistance of the conductor changes (due to an increase in its temperture), then the ratio of voltage to current obviously changes too -which means that it is not obeying Ohm's Law. If, on the other hand, an increasing current does not cause a change in resistance (because any increase in temperature does not cause an increase in resistance), then the ratio of voltage to current is constant, and the conductor IS obeying Ohm's Law.

Answer 3

For Ohm's Law to apply, the ratio of the current through a conductor or device to the voltage across that conductor or device must be constant for variations in voltage. In other words, if you were to draw a graph of current against variations in voltage, for Ohm's Law to apply, the result MUST be a straight line.

This isn't the case for semiconductors; their graphs are curved. So, in general, they do not obey Ohm's Law. Having said that, if you study such graphs, you will find that PARTS of those curves are straight lines. So Ohm's Law does apply to those parts of the graph that are straight but NOT to those parts which are curved.