Electronic Devices Chapter - Physics JEE Main

JEE Main Physics Chapters 

1

Units and Measurement

11

Electrostatics

2

Kinematics

12

Current Electricity

3

Laws of Motion

13

Magnetic Effects of Current and Magnetism

4

Work, Energy and Power

14

Electromagnetic Induction and Alternating Currents

5

Rotational Motion

15

Electromagnetic Waves

6

Gravitation

16

Optics

7

Properties of Solids and Liquids

17

Dual Nature of Matter

8

Thermodynamics

18

Atoms and Nuclei

9

Kinetic Theory of Gases

19

Electronic Devices

10

Oscillations and Waves

20

Communication Systems

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:

$I = I_0 e^{\dfrac{qV}{kT}} - 1$

• 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:

$I = I_s e^{\dfrac{qV}{nkT}} - 1$

• 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:

$V_{z}=V_{Z0}+(IR_{z}) V_{z}$

• 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:

$Av = -\beta \times \dfrac{Rc}{(Re + (1 + \beta) Re)}$

• 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: 

$Y=\bar A$

Universal Logic Gates

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

$Y= \bar {AB}$

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

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

Examples of Two-terminal Semiconductor

Examples of Three-terminal Semiconductor

DIAC

TRIAC

PIN Diode

Field Effect Transistor

Tunnel Diode

Darlington Transistor

Laser Diode

Thyristor

Schottky Diode

Silicon Controlled Rectifier (SCR)

Zener Diode

Unijunction Transistor

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): 

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

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