Characteristic Curves Of Components

NCERT Class 12, Chapter 14 describes the current-voltage characteristic of a p-n junction diode, which is markedly non-linear unlike an ohmic resistor. In forward bias, negligible current flows until the applied voltage overcomes the potential barrier of the depletion region; beyond this point, called the threshold or knee voltage (about 0.7 V for silicon), the current rises steeply. The described feature, near-zero current until a certain forward voltage, is exactly this threshold voltage. The option naming reverse breakdown voltage is wrong because that occurs in reverse bias, where a large current suddenly flows, not in the forward region described. The option naming peak inverse voltage is wrong because that is a maximum safe reverse voltage rating, not a forward turn-on feature. The option naming saturation current is wrong because that is the tiny constant reverse current, unrelated to the forward knee. In the experiment the diode is connected in forward bias through a series resistor to limit current, and readings of current against voltage are taken in small steps, becoming finer near the knee where the curve turns sharply upward. The knee voltage is roughly 0.7 V for silicon and 0.3 V for germanium, reflecting the different barrier potentials of the two materials. A consistency check confirms that the sharp onset of forward conduction after a barrier-overcoming voltage is precisely the knee voltage, which is why diode characteristics bend sharply near that point rather than following a straight ohmic line.