Physics MCQs for NEET — Practice Questions with Answers

In a P-N junction, there is no appreciable current when a potential difference is applied across the junction making the P section negative and the N section positive. This is because the P-N junction is reverse biased in this condition, leading to a high resistance and very little current flow.

The resistance of a P-N junction diode in forward biasing is a few ohms. In forward bias, the diode conducts current easily and has a low resistance.

When a P-N junction diode is in forward biased condition, the flow of current is mainly due to the diffusion of electrons. In forward bias, electrons from the N region diffuse into the P region and recombine with holes, leading to current flow.

When a junction diode is reverse biased, the potential barrier increases. This is because the reverse bias widens the depletion region, making it harder for charge carriers to cross the junction.

In a reverse-biased P-N junction diode, electrons and holes move away from the junction depletion region. This movement increases the width of the depletion region and the height of the potential barrier, limiting the flow of current.

The electrical resistance of the depletion layer is large because it has very few charge carriers. The depletion region is essentially devoid of free electrons and holes, making it an insulative barrier.

In a semiconductor diode, the barrier potential offers opposition to the majority carriers in both regions. In the N region, the majority carriers are electrons, and in the P region, the majority carriers are holes. The barrier potential prevents these majority carriers from diffusing across the junction, maintaining the depletion region.

In a Zener diode, at the breakdown voltage (V_Z), a large change in current produces an insignificant change in the voltage. This is known as the Zener effect, where the diode maintains a nearly constant voltage despite variations in the current, making it useful for voltage regulation applications.

The zener voltage of a zener diode is primarily determined by the level of doping in the semiconductor material. By changing the doping concentration, the breakdown voltage, and hence the zener voltage, can be set to a desired value. Adjusting the input voltage or current, or connecting a resistance in series, are not methods to set the zener voltage.