Semiconductor Electronics: Materials, Devices and Simple Circuits MCQs for NEET — Physics Questions with Answers

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.

In a junction diode, when reverse bias is applied, the potential barrier increases. This is because the negative terminal of the battery is connected to the n-side and the positive terminal to the p-side, resulting in an increase in the depletion region and a higher potential barrier.

In a common base configuration of a transistor, the alternating current gain (α) is defined as the ratio of the change in collector current (ΔI_C) to the change in emitter current (ΔI_E), with the collector voltage (V_c) held constant. Thus, $$ ext{α} = rac{ΔI_C}{ΔI_E} igg|_{V_c = const} $$.

In an N-P-N transistor circuit, the emitter current (I_E) is the sum of the base current (I_B) and the collector current (I_C). Therefore, the correct relationship is $$ I_E = I_B + I_C $$, which implies $$ I_B < I_C < I_E $$.

Ripples refer to the residual periodic variation of the DC voltage within a power supply which has been derived from an AC source. Essentially, it is the unwanted AC component present in the DC output of a rectifier. Thus, ripples are AC mixed with DC.

$ I_c =10 mA =0.90I_E $ $ \therefore I_E \approx 11 mA $ $ \therefore I_B \approx 1mA $

When a P-type semiconductor is heated, the thermal energy supplied increases the number of electron-hole pairs generated. This means that the number of electrons and holes increases equally due to the intrinsic carrier generation.