Final answer:
When a diode is forward biased and the bias voltage is increased, the voltage across the diode remains approximately constant, close to its threshold voltage, typically around 0.7 V for silicon diodes.
Step-by-step explanation:
When a diode is forward biased and the bias voltage increases, the voltage across the diode, according to the practical model, will not change significantly. This is because after the diode starts conducting (usually at about 0.7 V for silicon diodes), the voltage across the diode remains approximately constant even as the forward current increases. Instead, the current through the diode increases with increasing bias voltage, but the voltage across the diode in the forward-biased condition stays relatively stable near the diode's turn-on voltage threshold.