Physics MCQs for NEET — Practice Questions with Answers

An intrinsic semiconductor has a finite resistance that decreases with temperature. As temperature increases, more electron-hole pairs are generated, thereby increasing the number of charge carriers and decreasing the resistance.

The behavior of germanium (Ge) as a semiconductor is due to the width of the forbidden band being small and narrow. In semiconductors, the forbidden band (also called the band gap) is small enough to allow electrons to jump from the valence band to the conduction band at room temperature, thus allowing the material to conduct electricity.

The advantage of a PN junction diode over a tube valve that is not true is 'Unlimited life'. While PN junction diodes do have many advantages such as no warming-up time, large efficiency, and low power consumption, they do not have an unlimited lifespan. They can degrade over time due to factors such as heat and electrical stress.

$ \beta = { \alpha \over 1 -\alpha } $

At 0 K temperature, an N-type semiconductor does not have any charge carriers. At absolute zero, all the electrons in the semiconductor are bound to atoms and there is no thermal energy to excite electrons into the conduction band. Hence, there are no free charge carriers (electrons or holes) available for conduction.

In a silicon crystal, an impurity donor atom typically has a valency of 5. Such atoms are called pentavalent impurities and they donate extra electrons to the silicon crystal, making them n-type semiconductors. Examples of pentavalent impurities include phosphorus (P), arsenic (As), and antimony (Sb).

A full wave rectifier converts both halves of the AC input signal into pulsating DC. Therefore, the ripple frequency of a full wave rectifier is twice the frequency of the AC supply. Given the AC supply frequency is 50Hz, the ripple frequency will be 2 * 50Hz = 100Hz.