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

The depletion layer in a PN junction diode is caused by the diffusion of charge carriers. When a PN junction is formed, electrons from the N-region diffuse into the P-region and recombine with holes, and holes from the P-region diffuse into the N-region and recombine with electrons. This diffusion results in the creation of a region devoid of free charge carriers, known as the depletion layer.

In a solar cell, we aim to maximize the power output. A larger active junction area allows for the absorption of more light, which in turn generates more electron-hole pairs and increases the current produced by the solar cell. Hence, the active junction area in a solar cell is large to achieve more power.

To find the value of the limiting resistor ( $R$ ) for an LED, we use Ohm's law. Given the parameters: the voltage drop across the LED ( $V_{LED} = 2V$ ), the current through the LED ( $I = 10 mA$ ), and the supply voltage ( $V_{supply} = 6V$ ). The resistor value can be calculated as follows:

$$R = \frac{V_{supply} - V_{LED}}{I}$$

Substituting the values:

$$R = \frac{6V - 2V}{10 mA}$$

$$R = \frac{4V}{10 mA}$$

$$R = 400 \Omega$$

Thus, the value of the limiting resistor is $400 \Omega$ .

In intrinsic semiconductors, the number of electrons (y) is equal to the number of holes (x). This is because intrinsic semiconductors are pure and have no impurities, so the generation of electron-hole pairs is balanced.

Decreasing the temperature of a semiconductor increases its resistivity. This is because lower temperatures reduce the thermal energy available to generate electron-hole pairs, thereby reducing the number of charge carriers.

A Light Emitting Diode (LED) operates only in forward bias. In forward bias, the LED allows current to pass through and emits light. Varactor diodes, Zener diodes, and photodiodes either operate in reverse bias or can operate in both forward and reverse bias depending on their specific applications.

Only solar- cell generates e.m.f and it does not need bias -voltage

In forward bias mode, the P-N junction diode allows current to flow easily, resulting in a lower resistance. Therefore, the resistance of a P-N junction diode in forward bias is 'less'.