Physics - Semiconductors Question with Solution | TestHub

We studied ohm's law in the class. There are many devices that do not obey ohm's law. A very common and extremely useful device is a diode. A diode is an electronic device designed to conduct current in one direction and not in the other direction. In normal circuits, if we reverse the connection of a bulb, it still glows with the same brightness. But if a diode is reversed, the current drops to zero. The symbol for a diode is shown. The arrow points in the direction of conventional current allowed through the diode.

The graph compares current versus potential difference for a $3\Omega$ resistor and a silicon diode. The resistor obeys ohm's law and current can flow in either direction. A silicon diode starts conducting if there is a potential difference of $0.7\mathrm{V}$ across it or more. Above this value, it essentially behaves as a conductor. Below this threshold, it will not conduct current. The basic principle governing a diode can only be explained using quantum mechanics. Assume that once the diode starts conducting, it keeps conducting until the potential difference across it becomes negative.