Electronic Devices Chapter - Physics JEE Main

A smart way of preparation will help students in securing good grades in competitive exams like IIT-JEE and JEE-Main. ‘Electronic devices’ is one such important chapter that will definitely help students in securing good scores and boost their grades in the upcoming exams.

The electronic devices chapter introduces us to what is electronics and the types of electronics. The chapter includes the concepts of semiconductor physics. In this chapter, students will have exposure to the concepts of the conduction of electrons in different material types. We study the differences between the conductor, semiconductor and insulators with the help of the energy gap between the covalent and valence band. Further, in this chapter, we study the semiconductor and types of semiconductors classification depending on the doping method (Intrinsic and Extrinsic). 

In electronic devices, we study a few most important semiconductor devices such as diodes, and transistors in detail. At last, we will be moving towards digital electronics which is the fundamental and most interesting part of the chapter.

In this article, students will be provided with the content that will be a helping aid for their preparation. Let's start!!

JEE Main Physics Chapters 2024 

Important Topics of Electronic Devices Chapter

• Semiconductors

• Energy Bands In Solids 

• Classification of Materials

• PN-Junction diode

• Biasing Techniques

• PN-Junction Diode As A Rectifier

• Zener Diodes

• Transistors-NPN and PNP

• Transistor As an Oscillator

• Logic Gates

• De Morgan Theorems

Electronic Devices Important Concept of JEE Main

Concept Name	Key Points
Energy Bands in Solids	Valence Band: It is the band formed by the outermost electrons (valence electrons) which are strongly bound to the nuclei. Conduction Band: It is the band formed by the free electrons (conduction electrons) which are loosely bound to the nuclei.
Forbidden Energy Gap	Energy gap in any solid is the separation between the conduction and valence band
Classification of materials	Conductors: These are the semiconductor materials in which there will be a very small energy gap or no energy gap between the CB and VB Insulators: These are the solid materials in which the energy bandgap will be large enough, such that conduction will not be taking place. Semiconductors: These are the materials whose conductivity lies between conductors and insulators. The energy gap between these will be small but more than the conductors. Some of the Semiconductor electrical devices examples are transistors, diodes, etc…
Types of Semiconductors	Intrinsic Semiconductors: Intrinsic semiconductors are the pure form of semiconductors. Ge and Si are examples. Extrinsic Semiconductors: These are the type of semiconductors in which impurities will be added. Extrinsic semiconductors are further classified as N-type and P-type semiconductors.
N-type and P-type Semiconductors	N-type: These are the semiconductors formed by adding pentavalent impurities to the pure semiconductor. Here, electrons will be the majority charge carriers. P-type: These are the semiconductors formed by adding trivalent impurities to the pure semiconductors. Here, holes will be the majority charge carriers.
PN-Junction Diode	It is a two-terminal electronic device that helps in regulating the flow of electric current. The symbol of the PN-Junction diode is:
Biasing Methods	Forward biasing: If the positive terminal of an electronic device is connected to the positive and negative terminal, the negative terminal of the battery is known as forward biasing. So, in forward bias, the diode allows current to flow easily. The current (I) through the diode is given by the Shockley diode equation: $I=I_0{e}^{{\displaystyle \frac{qV}{kT}}}-1$ Reverse biasing: If the positive terminal of an electronic device is connected to the negative and negative terminal connected to the positive terminal of the battery is known as reverse biasing. So, in reverse bias, the diode blocks the current efficiently. A small reverse current, known as reverse leakage current, flows, which is governed by the diode's characteristics and temperature.
Diode As a Rectifier	Rectifiers: These are the electronic devices used for converting alternating current into direct current.
Half Wave Rectifier	Only half part of the ac signal will be rectified.
Full Wave Rectifier	The complete cycle of the ac signal will be converted into a dc signal.
I-V Characteristics of LED	Light Emitting Diodes (LEDs) are diodes that emit light when current flows through them. Their I-V characteristics differ from regular diodes. The voltage-current relationship for an LED is given by: $I=I_s{e}^{{\displaystyle \frac{qV}{nkT}}}-1$ Here, I_s is the saturation current, V is the voltage, n is the emission coefficient, and k and T have their previous meanings.
Photodiode, Solar Cell, and Zener Diode	Photodiode: A photodiode is a semiconductor device that converts light into electrical current. The photocurrent generated is directly proportional to the incident light intensity. It operates in reverse bias, and its reverse current increases with increasing light intensity. Solar Cell: A solar cell is a photovoltaic device that converts sunlight into electricity. It works on the same principle as a photodiode but is designed to produce a significant amount of power. Zener Diode: A Zener diode operates in reverse bias, just like a regular diode. However, it is designed to work in the breakdown region, known as the Zener breakdown. It maintains a constant voltage across its terminals and is often used as a voltage regulator.
Zener Diode as a Voltage Regulator	The voltage across a Zener diode is given by: $V_z=V_{Z0}+(I{R}_z)V_z$ Where $V_{z0}$ is the Zener voltage, I is the current, and $R_z$ is the dynamic resistance.
Transistors	These are the three-terminal electronic devices used for the amplification process. Transistors consist of an emitter, base and collector. A transistor is made by sandwiching two pn-junction diodes back to back. There are two types of transistors PNP and NPN, depending on the majority charge carriers.
Transistor as an Amplifier, Oscillator, and as Switch	Transistor as an Amplifier: In the common emitter configuration, the transistor amplifies the input signal. The voltage gain (Av) is given by: $Av=-\beta \times {\displaystyle \frac{Rc}{(Re+(1+\beta )Re)}}$ Transistor as an Oscillator: A transistor can also function as an oscillator, generating periodic signals. It does so by utilizing positive feedback. Transistor as a Switch: Transistors can be used as electronic switches, where a small signal at the base controls a much larger current flow between the collector and emitter. This switching capability is essential in digital logic and power control applications.
Logic gates	Logic gates are the building blocks of digital electronics.  The logic gates are basically the devices used to perform mathematical operations using bits 0 and 1.  Logic gates are two or more inputs and single output devices. There are three basic gates: OR, AND and NOT. Two universal gates: NAND Aand NOT
Basic Logic Gates	OR Gate: These are the logic gates used to perform addition. Boolean expression:  Y= A+B AND Gate: These are the logic gates used to perform multiplication. Boolean expression:  Y= AB NOT Gate: These are the logic gates used to perform complementary functions. Boolean expression:  $Y=\overline{A}$
Universal Logic Gates	NAND Gate: It is the combination of NOT and AND gates. $Y=\overline{AB}$ NOR Gate: It is the combination of NOT and OR gates. $Y=Y=\overline{A+B}$

Types of Transistors:

Transistors come in two main types: NPN transistors and PNP transistors.

NPN Transistor:

An NPN transistor has a thin P layer sandwiched between two thick N layers.

PNP Transistor:

For a PNP transistor, a thin N layer is sandwiched between two thick P layers.

Logic Gates:

Logic gates show the logical relationship between input and output voltage. A truth table lists all possible combinations of inputs and outputs.

Basic Logic Gates:

The three basic logic gates are AND, OR, and NOT.

AND Gate:

In an AND gate, if all inputs are high, the gate goes to the high state. For example, if both A and B are true, the output (Y) is true (Y = A.B).

The Truth Table of AND:

Doping Semiconductor Material

Doping process highly increases the number of charge carriers within the crystal. If a doped semiconductor material contains more free holes it is called "p-type", and when it contains more free electrons it is known as "n-type".

N-type (e.g. Doped with Antimony)

In N-type semiconductors the characteristics are as follows:

1. The Donors are positively charged.

2. A large number of free electrons.

3. A small number of holes in relation to the number of free electrons.

4. Doping gives positively charged donors and negatively charged free electrons.

5. Supply of energy gives negatively charged free electrons and positively charged holes.

P-type (e.g. Doped with Boron) 

In these, types of materials have characteristics as follows:

1. The Acceptors are negatively charged.

2. There are a large number of holes.

3. A small number of free electrons in relation to the number of holes.

4. Doping gives negatively charged acceptors and-positively charged holes.

5. Supply of energy gives positively charged holes and negatively charged free electrons.

Properties of Semiconductors

Under ideal conditions or circumstances, semiconductor devices are able to conduct electricity. However, there are a number of other attributes to consider.

• An increase in temperature (applying heat) results in an increase in the conductivity of the semiconductor.

• Electrons and holes flow along the semiconductor.

• This results in reduced power loss.

• Performing doping increases the efficiency of semiconductor devices.

• As the temperature rises, resistance decreases.

Examples of Semiconductor Devices

List of Important Formulas for Electronic Devices Chapter

JEE Main Electronic Devices Solved Examples

1. Draw and explain the output waveform across the load resistor R, if the input waveform is as shown in the given figure.

Sol:

Given,

A square wave is used as a signal, now we are asked to determine the output waveform when the signal is passed through the load resistor R.

Here, we will consider two different conditions:

1. When the input signal +5V: 

With +5 V input, the pn-junction diode will be forward biased and +5 V voltage will pass through the load resistance.

2. When the input signal -5V: 

With -5 V input, the pn-junction diode will be reverse biased and no voltage will pass through the load resistance.

Therefore, the output waveform will be as shown below:

Key Point: When the pn-junction diode is reverse biased the voltage across the resistor will be zero.

2. In an unbiased p-n junction diode, holes tend to diffuse from the p-region to n-region, due to

1. hole concentration in p-region is more as compared to n-region.

2. they move across the junction by the potential difference.

3. free electrons in the n-region attract them.

4. All the above

Sol: 

The right answer is option a.

Reason: In an unbiased pn junction diode, holes tend to diffuse from the p-region to n-region, because, in p-region is having abundant holes which will attract the electrons in the n-region.

Key point: The charge carriers always move from higher concentration to lower concentration. In this question, we can see that p-region having more number of holes than in n-region.

Previous Year Questions From Electronic Devices

1. Identify the logic operation carried out by the given circuit

1. OR

2. AND

3. NOR

4. NAND

Sol:

Given, 

On analysing the logic circuit we found that,

$Z=\overline{A}.\overline{B}=\overline{A+B}$= NOR gate

Therefore, Option C is the right answer.

Trick: Whenever we come across a complimentary function we should remember that De morgan’s theorem will solve the equation easily.

2. For the given circuit, the power across zener diode is ………..mW.

Sol:

Given, an electric circuit with zener diode. Now we are asked to determine the power across the zener diode.

Let us solve the circuit first:

$I_L={\displaystyle \frac{10}{5}}=2mA$

I=141=14 mA$I={\displaystyle \frac{14}{1}}=14mA$

$I_Z=I-I_L=14-2=12mA$

Therefore, power across zener diode is:

$P_Z=I_Z{V}_Z=12mA\times 10=12omW$

Trick: Voltage across the parallel components will always be equal.

Practice Questions From Electronic Devices

1. In a pure, or intrinsic, semiconductor, valence band holes and conduction-band electrons are always present 

1. None of these

2. such that number of holes is greater than the number of electrons

3. in equal numbers

4. such that number of electrons is greater than the number of holes

(Ans: Option C)

2. When Ge crystal is doped with phosphorus atoms, it becomes

1. superconductor

2. Insulator

3. n-type

4. p-type

(Ans: Option C)

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Conclusion

In this article, we dove into the exciting world of Electronic Devices in your JEE Main physics chapter. We covered all the essential concepts and solutions to common questions you might encounter. You'll discover the ins and outs of electronic components and how they work together to create various electronic devices. We've also got easy-to-understand PDFs for you to download, which will help you grasp these concepts and be well-prepared for your exams. So, get ready to explore the fascinating realm of Electronic Devices, and ace your physics exam with confidence!