CBSE Questions for Class 12 Engineering Physics Semiconductor Electronics: Materials,Devices And Simple Circuits Quiz 6 - MCQExams.com

Hint:

The NAND Gate has two or more input but only one output. The output of NAND gate is high if atleast any one of the input is low. The symbol of NAND gate is as shown,           

The truth table for 2-input NAND gate is as given,

Step 1: Using Boolean Algebra.

According to the given circuit, the output is,

$$Y=\overline{\left( \overline{A.B} \right)}$$

$$\Rightarrow Y=A.B$$

Which is the output for AND gate. Thus the combination of circuit act as an AND gate.

Step 2: Using Truth Table.

Truth Table for the given circuit is as given below,

$$\textbf{Hint: IV group elements are Semiconductors}$$

$$\textbf{Correct options are (C) and (D).}$$

$$\textbf{Explanation}:$$

Semiconductors are materials that have electrical conductivities between conductors and insulators. The valence band ($${{E}_{V}}$$ ) and the conduction band ($${{E}_{C}}$$ ) in the conductors overlap each other whereas in the insulators the bandgap ($${{E}_{G}}$$ ) between the two bands is more than 6eV, in semiconductors, this gap is very less and hence with small energy transfer electrons in the valence band (bound state) of semiconductors can jump to the conduction band (free state).

Valence Band ($${{E}_{V}}$$ ): Lower energy level which contains the valence electrons.

Conduction Band ($${{E}_{C}}$$ ): The energy level in which electrons can be considered free.

Band Gap ($${{E}_{G}}$$ ): It is the gap in energy between the valence band and the conduction band.

Example of Semiconductors: They can be of different kinds but the most common elemental semiconductors are Silicon (Si), Germanium (Ge), and Tin (Sn) and there can be compound semiconductors such as Gallium arsenide (GaAs) which is formed from a combination of group III and group V elements.

When a diode is connected in a Zero Bias condition, no external potential energy is applied to the PN junction. However if the diodes terminals are shorted together, a few holes (majority carriers) in the P-type material with enough energy to overcome the potential barrier will move across the junction against this barrier potential. This is known as the Forward Current.

Likewise, holes generated in the N-type material (minority carriers), find this situation favourable and move across the junction in the opposite direction. This is known as the Reverse Current and is referenced as IR. This transfer of electrons and holes back and forth across the PN junction is known as diffusion.

Then an Equilibrium or balance will be established when the majority carriers are equal and both moving in opposite directions so that the net result is zero current flowing in the circuit. When this occurs the junction is said to be in a state of Dynamic Equilibrium.

The energy band gap is the energy difference between 2 bands i.e. valence band and the conduction band. In case of conductors, energy band gap is very small almost overlapping whereas, in case of insulators, the band gap is ∼6 eV. So. band gap of conductors is less than insulators.