AL phy 2008年paper2 第15題(有圖)

Because statement (2) doesn't satisfy Ohm's Law.

Ohm's Law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.

[Ref: http://en.wikipedia.org/wiki/Ohm's_law ]

In other words, the resistance = voltage/current. It is not the increase of voltage to the increase of current.

Clearly, the graph on the diagram doesn't show that current and voltage are directly proportional.



2011-02-05 00:18:08 補充：
A substance that obeys Ohm's Law is said to be an Ohmic Substance. Those that do not obey Ohm's Law have resistances. It is only that their resistances depend on the applied voltage and are not constant. An example is a diode, the resistance of which doesn't obey Ohm's Law.