JEE 2022 | Class 12

JEE Important Chapter - Electronic Devices

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A Detailed Information About Electronic Devices For JEE Preparation

A Detailed Information About Electronic Devices For JEE Preparation

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!!

Important Topics of Electronic Devices

  • 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


Important Concepts of Electronic Devices

Sl. No

Concept Name

Key Points

1.

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.

2. 

Forbidden Energy Gap

  • Energy gap in any solid is the separation between the conduction and valence band

3. 

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…

4.

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.

5. 

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.

6.

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:

PN-Junction Diode

7.

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.

  • 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.

8. 

Diode As a Rectifier

Rectifiers: These are the electronic devices used for converting alternating current into direct current.

9.

Half Wave Rectifier

Only half part of the ac signal will be rectified.

Half Wave Rectifier

Half Wave Rectifier

10. 

Full Wave Rectifier

The complete cycle of the ac signal will be converted into a dc signal.

Full Wave Rectifier

Full Wave Rectifier

11.

Transistors

  • These are the three-terminal electronic devices used for the amplification process.

  • Transistors consist of an emitter, base and collector.

Transistors

  • 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.

12.

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


13. 

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: 

$Y=\bar A$

Basic Logic Gates

14. 

Universal Logic Gates

  • NAND Gate: It is the combination of NOT and AND gates.

$Y= \bar {AB}$

Universal Logic Gates

  • NOR Gate: It is the combination of NOT and OR gates.

$Y=Y=\overline{A+B}$

Universal Logic Gates


List of Important Formulae in Electronic Devices

Sl. No

Concept Name

Formula

1. 

Mass Action Law

The product of the concentrations of free electrons 'ne' and holes 'nh' is a constant in thermal equilibrium, and it is independent of the amount of doping by acceptor and donor impurities.

${n_e}\times {n_h}={n_i}^2$

2. 

Form Factor

For Full Wave Rectifier:

$F=\dfrac {\pi}{2\sqrt {2}}$


For Half Wave Rectifier:

$F=\dfrac {\pi}{2}$

3.

RMS Value of Current

$I_{rms}=\sqrt {{I_{dc}}^2 +{I_{ac}}^2}$

4. 

Ripple Factor

$r=\dfrac {I_{ac}}{I_{dc}}=\sqrt {{F^2}-1}$

5.

Electrical conductivity of semiconductors

Intrinsic semiconductor:-

  • σ = e(neμe + nhμh)

  • $\sigma={\sigma_o}e^{\dfrac {E_g}{kT}}$


Extrinsic semiconductor:-

  • N-type: σ = eneμe

  • P-type: σ = ennμn

6.

Transistors

Relation between the currents in the transistors:

IE=IC+IB (IB << IE, IB<<IC)

Current gain

$\alpha=\dfrac {I_C}{I_E}$

$\beta=\dfrac {I_C}{I_B}$

7. 

Relation Between the and

$\alpha=\dfrac {\beta}{1+\beta}$ and

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

8.

Voltage gain

$A_v=\dfrac {V_{out}}{V_{in}}$

9.

De Morgan’s Theorems

$\overline{A+B}=\bar {A} . \bar {B}$

$\overline{A.B}=\bar {A} + \bar {B}$

10.

Miscellaneous Formulae

Triodes: A vacuum tube containing three elements namely plate, filament and grid.

Plate resistance (rp):

$r_p=\left (\dfrac {\Delta {V_P}}{\Delta {I_P}}\right)_{{V_g}=Constant}$

Mutual Inductance (gm): 

$g_m=\left (\dfrac {\Delta {I_P}}{\Delta {V_g}}\right)_{{V_P}=Constant}$


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.


Waveform


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.

  1. 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:


Waveform


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


  1. 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


Logic Operation


  1. OR

  2. AND

  3. NOR

  4. NAND

Sol:

Given, 


Logic Circuit


On analysing the logic circuit we found that,

$Z=\bar {A}. \bar {B}=\overline{A+B}$= 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.


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


Zener Diode


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:

$I_L=\dfrac {10}{5}=2 mA$

I=141=14 mA$I=\dfrac {14}{1}=14 mA$

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

Therefore, power across zener diode is:

$P_Z = {I_Z}{V_Z}=12 mA \times 10=12o mW$


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)


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

  1. superconductor

  2. Insulator

  3. n-type

  4. p-type

(Ans: Option C)


Conclusion

In this article, we have gone through the most important concepts of electronic devices. We have seen a few solved examples which are tricky yet simple to tackle. We can see that there are many applications of electronics in terms of various devices with different purposes. In this article, we have also added a few important questions from previous year's question papers. Students are required to solve more and more questions to ace the exam.

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JEE Main 2022 June and July Session exam dates and revised schedule have been announced by the NTA. JEE Main 2022 June and July Session will now be conducted on 20-June-2022, and the exam registration closes on 5-Apr-2022. You can check the complete schedule on our site. Furthermore, you can check JEE Main 2022 dates for application, admit card, exam, answer key, result, counselling, etc along with other relevant information.
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JEE Main 2022 Study Material

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JEE Main 2022 state rank lists will be released by the state counselling committees for admissions to the 85% state quota and to all seats in NITs and CFTIs colleges. JEE Main 2022 state rank lists are based on the marks obtained in entrance exams. Candidates can check the JEE Main 2022 state rank list on the official website or on our site.
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NTA is responsible for the release of the JEE Main 2022 June and July Session cut off score. The qualifying percentile score might remain the same for different categories. According to the latest trends, the expected cut off mark for JEE Main 2022 June and July Session is 50% for general category candidates, 45% for physically challenged candidates, and 40% for candidates from reserved categories. For the general category, JEE Main qualifying marks for 2021 ranged from 87.8992241 for general category, while for OBC/SC/ST categories, they ranged from 68.0234447 for OBC, 46.8825338 for SC and 34.6728999 for ST category.
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FAQs on JEE Important Chapter - Electronic Devices

FAQ

1. Is Semiconductor devices a simple chapter for JEE?

Semiconductors and communication are relatively challenging to deal with. Certain factors must be kept in mind, and your concepts must be clear. You must also memorise a few things in addition to understanding the material. It is a crucial chapter for jee main, and students should study it thoroughly.

2. What is the importance of the electronic devices chapter for JEE?

Minimum of 2-3 questions will appear from this chapter, which covers 3% of the JEE total score. One of the easiest chapters of physics to score in JEE.

3. How to prepare the electronic devices chapter?

Students must prepare for the electronic devices by solving previous year's questions and NCERT solutions.