Fundamentals of Electronics (4311102) - Winter 2023 Solution

Question 1(a) [3 marks]

#

Define Forward and reverse bias of diode.

Answer:

Forward Bias of Diode:

• Connection Method: P-type connected to positive terminal and N-type connected to negative terminal of battery
• Barrier Width: Barrier width decreases
• Resistance: Low resistance (typically 100-1000Ω)
• Current Flow: Allows current to flow easily through the diode

Reverse Bias of Diode:

• Connection Method: P-type connected to negative terminal and N-type connected to positive terminal
• Barrier Width: Barrier width increases
• Resistance: Very high resistance (typically several MΩ)
• Current Flow: Blocks current flow (only small leakage current flows)

Diagram:

graph LR
    A[Forward Bias] --> B[P connected to +ve
N connected to -ve]
    A --> C[Current flows easily]
    D[Reverse Bias] --> E[P connected to -ve
N connected to +ve]
    D --> F[Current blocked]

Mnemonic: “PFNR” - “Positive to P Forward, Negative to P Reverse”

Question 1(b) [4 marks]

#

Explain construction and working of LDR.

Answer:

Construction of LDR:

• Material: Made of semiconductor material (Cadmium Sulfide)
• Pattern: Zigzag pattern of photosensitive material on ceramic base
• Electrodes: Metal electrodes at both ends
• Package: Encapsulated in transparent plastic or glass case

Working Principle:

• Photoconductivity: Based on photoconductivity principle
• Dark Resistance: High resistance (MΩ range) in dark conditions
• Light Exposure: When exposed to light, photons release electrons
• Resistance Drop: Resistance decreases (kΩ range) in bright light

Diagram:

Mnemonic: “MILD” - “More Illumination, Less Dark-resistance”

Question 1(c) [7 marks]

#

Explain the color band coding method of Resistor. Write color band of 47kΩ ±5% resistance.

Answer:

Color Band Coding Method:

4-Band Resistor Color Code:

• First Band: First significant digit
• Second Band: Second significant digit
• Third Band: Multiplier
• Fourth Band: Tolerance

For 47kΩ ±5%:

• First digit: 4 = Yellow
• Second digit: 7 = Violet
• Multiplier: 10³ = Orange (for kΩ)
• Tolerance: ±5% = Gold

Color bands for 47kΩ ±5%: Yellow-Violet-Orange-Gold

Diagram:

Mnemonic: “BAND” - “Beginning digits, Amplify with Multiplier, Note tolerance with last band, Decode carefully”

Question 1(c) [7 marks] (OR)

#

Explain Aluminum Electrolytic wet type capacitor.

Answer:

Aluminum Electrolytic Wet Type Capacitor:

Construction:

• Plates: Two aluminum foils (anode and cathode)
• Dielectric: Aluminum oxide layer on anode foil
• Electrolyte: Liquid electrolyte (boric acid, sodium borate, etc.)
• Separator: Paper separator soaked in electrolyte
• Enclosure: Aluminum can with rubber seal

Working Principle:

• Oxide Layer: Thin aluminum oxide layer acts as dielectric
• Electrolyte: Acts as cathode connection to second plate
• Polarization: Has defined polarity (+ and -) terminals

Characteristics:

• Capacitance Range: 1μF to 47,000μF
• Voltage Rating: 6.3V to 450V
• Polarity: Polarized (must connect correctly)
• Leakage Current: Higher than other capacitor types
• ESR: Higher equivalent series resistance

Diagram:

graph TD
    A[Aluminum Electrolytic Capacitor] --> B[Aluminum Can]
    A --> C[Anode Foil]
    A --> D[Cathode Foil]
    A --> E[Electrolyte]
    A --> F[Separator]
    A --> G[Aluminum Oxide Layer]
    A --> H[Terminal Posts]

Mnemonic: “POLE” - “Polarized, Oxide layer, Liquid electrolyte, Enormous capacitance”

Question 2(a) [3 marks]

#

Draw the symbol of Schottkey diode, LED and Photo-diode.

Answer:

Symbols:

Key Features:

• Schottky Diode: Standard diode symbol with curved bar (represents metal-semiconductor junction)
• LED: Standard diode symbol with two arrows pointing away (represents light emission)
• Photo-diode: Standard diode symbol with two arrows pointing toward diode (represents light detection)

Mnemonic: “SLP” - “Schottky has curve, LED emits, Photo-diode absorbs”

Question 2(b) [4 marks]

#

Define Active and Passive Components with example.

Answer:

Passive Components:

Active Components:

Diagram:

graph TB
    A[Electronic Components] --> B[Active Components]
    A --> C[Passive Components]
    B --> D[Transistors]
    B --> E[ICs]
    B --> F[Amplifiers]
    C --> G[Resistors]
    C --> H[Capacitors]
    C --> I[Inductors]

Mnemonic: “PASS-ACT” - “Passive stores or dissipates, Active controls or amplifies”

Question 2(c) [7 marks]

#

Explain working of full wave bridge rectifier.

Answer:

Full Wave Bridge Rectifier:

Circuit Construction:

• Diodes: Four diodes arranged in bridge configuration
• Input: AC supply from transformer secondary
• Output: Pulsating DC across load resistor with filter capacitor

Working Principle:

• Positive Half Cycle: D1 and D3 conduct, D2 and D4 block
• Negative Half Cycle: D2 and D4 conduct, D1 and D3 block
• Current Flow: Always flows through load in same direction

Performance Parameters:

• Ripple Frequency: 2× input frequency (100 Hz for 50 Hz input)
• Efficiency: 81.2%
• PIV: V₀(max) per diode
• TUF: 0.812 (Transformer Utilization Factor)

Diagram:

graph TD
    A[AC Input] --> B[Bridge Rectifier]
    B --> C[D1]
    B --> D[D2]
    B --> E[D3]
    B --> F[D4]
    C --> G[Load]
    D --> G
    E --> G
    F --> G
    G --> H[Pulsating DC Output]
    H --> I[Filter Capacitor]
    I --> J[Smooth DC Output]

Mnemonic: “BRIDGE” - “Better Rectification with Improved Diode Geometry Efficiency”

Question 2(a) [3 marks] (OR)

#

Explain construction and working of LED.

Answer:

Construction of LED:

• Material: Semiconductor (GaAs, GaP, AlGaInP, etc.)
• Junction: P-N junction with heavily doped semiconductors
• Package: Encased in transparent or colored epoxy lens
• Cathode: Identified by flat side on package or shorter lead

Working Principle:

• Forward Bias: Applied to P-N junction
• Recombination: Electrons and holes recombine at junction
• Energy Release: Energy released as photons (light)
• Wavelength: Determined by band gap of semiconductor material

Diagram:

Mnemonic: “LEDS” - “Light Emits During electron-hole recombination in Semiconductor”

Question 2(b) [4 marks] (OR)

#

Explain composition type resistors.

Answer:

Composition Resistors:

Construction:

• Core Material: Carbon particles mixed with insulating material (clay/ceramic)
• Binding: Resin binder forms solid cylindrical shape
• Terminals: Metal caps with leads attached to ends
• Protection: Coated with insulating paint or plastic

Characteristics:

• Resistance Range: 1Ω to 22MΩ
• Power Rating: 1/8W to 2W
• Tolerance: ±5% to ±20%
• Temperature Coefficient: -500 to +500 ppm/°C

Advantages & Limitations:

• Cost: Low cost
• Noise: Higher noise level
• Stability: Less stable with temperature
• Applications: General purpose, non-critical applications

Diagram:

Mnemonic: “CCRI” - “Carbon Composition Resistors are Inexpensive”

Question 2(c) [7 marks] (OR)

#

Explain working of full wave rectifier with two diodes.

Answer:

Full Wave Rectifier with Two Diodes (Center-tap):

Circuit Construction:

• Transformer: Center-tapped transformer secondary
• Diodes: Two diodes connected to opposite ends of secondary
• Output: Taken between center tap and diode junction

Working Principle:

• Positive Half Cycle: Upper half of secondary positive, D1 conducts, D2 blocks
• Negative Half Cycle: Lower half of secondary positive, D2 conducts, D1 blocks
• Current Flow: Always flows through load in same direction

Performance Parameters:

• Ripple Frequency: 2× input frequency (100 Hz for 50 Hz input)
• Efficiency: 81.2%
• PIV: 2V₀(max) per diode (twice the center-tap rectifier)
• TUF: 0.693 (Transformer Utilization Factor)

Diagram:

graph TD
    A[AC Input] --> B[Center-Tapped Transformer]
    B -->|Upper Half| C[D1]
    B -->|Lower Half| D[D2]
    B -->|Center Tap| E[Ground]
    C --> F[Load]
    D --> F
    F --> E
    F --> G[Pulsating DC Output]
    G --> H[Filter]
    H --> I[Smooth DC Output]

Mnemonic: “CTFWR” - “Center Tap Facilitates Whole-cycle Rectification”

Question 3(a) [3 marks]

#

Explain working of schhotkey diode.

Answer:

Working of Schottky Diode:

• Junction Type: Metal-Semiconductor (M-S) junction instead of P-N
• Charge Carriers: Majority carrier device (electrons in N-type)
• Barrier: Schottky barrier formed at metal-semiconductor interface
• Forward Voltage: Lower forward voltage drop (0.2-0.4V vs 0.7V for Si diode)

Key Characteristics:

• Switching Speed: Very fast switching (no minority carrier storage)
• Applications: High-frequency circuits, power supplies
• Recovery Time: Negligible reverse recovery time

Diagram:

Mnemonic: “SFAM” - “Schottky’s Fast And Metal-based”

Question 3(b) [4 marks]

#

Explain N type semiconductor.

Answer:

N-type Semiconductor:

Formation:

• Base Material: Intrinsic semiconductor (Silicon or Germanium)
• Doping Element: Pentavalent impurity (P, As, Sb)
• Doping Process: Thermal diffusion or ion implantation
• Concentration: Typically 1 part impurity to 10⁸ parts silicon

Characteristics:

• Majority Carriers: Electrons (negative charge carriers)
• Minority Carriers: Holes
• Conductivity: Higher than intrinsic semiconductor
• Fermi Level: Closer to conduction band

Diagram:

graph TD
    A[N-type Semiconductor] --> B[Silicon Atom]
    A --> C[Pentavalent Impurity Atom]
    C --> D[Extra Free Electron]
    A --> E[Majority Carriers: Electrons]
    A --> F[Minority Carriers: Holes]

Mnemonic: “PENT” - “Pentavalent Element makes N-Type with free electrons”

Question 3(c) [7 marks]

#

Explain construction and working of PN Junction Diode.

Answer:

Construction of PN Junction Diode:

• Materials: P-type and N-type semiconductor regions
• Junction: Formed by diffusion or epitaxial growth
• Depletion Region: Forms at junction interface
• Contacts: Metal contacts attached to both regions
• Packaging: Sealed in glass, plastic, or metal case

Working Principle:

• Depletion Region: Forms due to diffusion of carriers
• Barrier Potential: Created across junction (0.7V for Si, 0.3V for Ge)
• Forward Bias: Current flows when forward voltage > barrier potential
• Reverse Bias: Only small leakage current flows until breakdown

Diagram:

Mnemonic: “BIRD” - “Barrier forms at Interface, Rectifies Direct current”

Question 3(a) [3 marks] (OR)

#

Explain working of photo-diode.

Answer:

Working of Photo-diode:

• Operation Mode: Reverse biased P-N junction
• Light Absorption: Photons create electron-hole pairs in depletion region
• Carrier Generation: Light energy > band gap energy creates free carriers
• Current Flow: Photocurrent proportional to light intensity

Key Characteristics:

• Sensitivity: Depends on semiconductor material and wavelength
• Response Time: Very fast (ns range)
• Operating Modes: Photovoltaic mode or photoconductive mode
• Applications: Light sensors, optical communication

Diagram:

Mnemonic: “PLIP” - “Photons Lead to Increased Photocurrent”

Question 3(b) [4 marks] (OR)

#

Explain P type Semiconductor.

Answer:

P-type Semiconductor:

Formation:

• Base Material: Intrinsic semiconductor (Silicon or Germanium)
• Doping Element: Trivalent impurity (B, Al, Ga)
• Doping Process: Thermal diffusion or ion implantation
• Concentration: Typically 1 part impurity to 10⁸ parts silicon

Characteristics:

• Majority Carriers: Holes (positive charge carriers)
• Minority Carriers: Electrons
• Conductivity: Higher than intrinsic semiconductor
• Fermi Level: Closer to valence band

Diagram:

graph TD
    A[P-type Semiconductor] --> B[Silicon Atom]
    A --> C[Trivalent Impurity Atom]
    C --> D[Hole Formation]
    A --> E[Majority Carriers: Holes]
    A --> F[Minority Carriers: Electrons]

Mnemonic: “TRIP” - “TRIvalent impurity Produces holes in P-type”

Question 3(c) [7 marks] (OR)

#

Compare half wave and full wave rectifier.

Answer:

Comparison between Half Wave and Full Wave Rectifier:

Diagram:

graph TD
    A[Rectifiers] --> B[Half Wave]
    A --> C[Full Wave]
    C --> D[Center-Tapped]
    C --> E[Bridge]
    B --> F[Uses 1 diode]
    B --> G[Lower efficiency]
    D --> H[Uses 2 diodes]
    E --> I[Uses 4 diodes]
    C --> J[Higher efficiency]

Mnemonic: “HERO” - “Half wave: Efficiency Reduced, One-half cycle only”

Question 4(a) [3 marks]

#

Draw the symbol and construction of PNP and NPN transistor with proper notation.

Answer:

Transistor Symbols and Construction:

Construction:

Mnemonic: “NIN-PIP” - “N-P-N layers for NPN, P-N-P layers for PNP”

Question 4(b) [4 marks]

#

Explain working of Transistor amplifier.

Answer:

Working of Transistor Amplifier:

Circuit Configuration:

• Common Emitter: Most commonly used
• Biasing: Proper DC bias provided to operate in active region
• Coupling: Input/output coupling through capacitors
• Load: Collector resistor as load

Working Principle:

• Input Signal: Applied to base-emitter junction
• Base Current: Small base current controls larger collector current
• Amplification: Small input voltage variations cause larger output voltage variations
• Phase Shift: 180° phase shift between input and output

Key Parameters:

• Voltage Gain: A_v = V_out/V_in
• Current Gain: β = I_c/I_b
• Input Impedance: Typically 1-2kΩ in CE configuration

Diagram:

graph TD
    A[Input Signal] --> B[Base Current]
    B --> C[Controls Collector Current]
    C --> D[Voltage Drop Across RC]
    D --> E[Amplified Output Signal]

Mnemonic: “ABCD” - “Amplification through Base Controlled collector Current Dynamics”

Question 4(c) [7 marks]

#

Explain working of Zener diode.

Answer:

Working of Zener Diode:

Basic Structure:

• Junction: Heavily doped P-N junction
• Construction: Similar to normal diode but optimized for breakdown
• Breakdown: Designed to operate in reverse breakdown region

Working Principle:

• Forward Bias: Acts like normal diode
• Reverse Bias:
  • Below breakdown: Small leakage current
  • At breakdown: Sharp increase in current at Zener voltage
  • Beyond breakdown: Maintains constant voltage

Breakdown Mechanisms:

• Zener Effect: Dominant below 5V (direct tunneling)
• Avalanche Effect: Dominant above 5V (impact ionization)

Applications:

• Voltage Regulation: Maintains constant output voltage
• Reference Voltage: Precise voltage reference
• Overvoltage Protection: Protects sensitive components

Diagram:

Mnemonic: “ZEBRA” - “Zener Effect Breaks at Regulated Avalanche voltage”

Question 4(a) [3 marks] (OR)

#

Explain transistor as a switch.

Answer:

Transistor as a Switch:

Operating Regions:

• Cutoff Region: Transistor OFF (I_B = 0, I_C ≈ 0)
• Saturation Region: Transistor ON (I_B > I_C/β, V_CE ≈ 0.2V)

Switching Operation:

• OFF State: No base current, high V_CE, acts as open switch
• ON State: Sufficient base current, low V_CE, acts as closed switch

Switching Characteristics:

• Turn-ON Time: Time to go from cutoff to saturation
• Turn-OFF Time: Time to go from saturation to cutoff

Diagram:

graph TD
    A[Transistor Switch] --> B[OFF State: Cutoff Region]
    A --> C[ON State: Saturation Region]
    B --> D[IB = 0, IC ≈ 0]
    B --> E[High VCE ≈ VCC]
    C --> F[IB > IC/β]
    C --> G[Low VCE ≈ 0.2V]

Mnemonic: “COST” - “Cutoff Off, Saturation Turns-on”

Question 4(b) [4 marks] (OR)

#

Draw and Explain characteristics of CE amplifier.

Answer:

CE Amplifier Characteristics:

Input Characteristics:

• Plot: I_B vs V_BE at constant V_CE
• Behavior: Resembles forward-biased diode curve
• Knee Voltage: Approximately 0.7V for silicon
• Input Resistance: Slope of curve (ΔV_BE/ΔI_B)

Output Characteristics:

• Plot: I_C vs V_CE at constant I_B
• Regions:
  • Saturation (V_CE < 0.2V)
  • Active (V_CE > 0.2V)
  • Cutoff (I_B = 0)
• Early Effect: Slight increase in I_C with increasing V_CE

Diagram:

Mnemonic: “IAOC” - “Input curves At Origin, Output curves show Current gain”

Question 4(c) [7 marks] (OR)

#

Explain working of Varactor diode.

Answer:

Working of Varactor Diode:

Basic Structure:

• Junction: Special P-N junction diode
• Operation: Always operated in reverse bias
• Property: Junction capacitance varies with reverse voltage

Working Principle:

• Depletion Layer: Widens with increasing reverse voltage
• Capacitance Effect: Depletion region acts as dielectric between P and N regions
• Capacitance Formula: C ∝ 1/√V_R
• Tuning Range: Typically 4:1 to 10:1 capacitance

Applications:

• Voltage-Controlled Capacitor: In electronic tuning circuits
• Frequency Modulation: In voltage-controlled oscillators (VCOs)
• Automatic Frequency Control: In receivers
• Parametric Amplification: In microwave circuits

Diagram:

graph TD
    A[Varactor Diode] --> B[Reverse Bias Operation]
    B --> C[Depletion Region Width]
    C --> D[Junction Capacitance]
    D --> E[Changes with Applied Voltage]
    E --> F[Electronic Tuning]

Mnemonic: “VCAP” - “Voltage Controls cAPacitance”

Question 5(a) [3 marks]

#

Define Active, Saturation and Cut-off region for transistor amplifier.

Answer:

Transistor Regions of Operation:

Diagram:

Mnemonic: “ASC” - “Active for Signals, Saturation & Cutoff for switches”

Question 5(b) [4 marks]

#

If the value of I_C = 10mA and I_B = 100μA then find the value of current gains α and β.

Answer:

Given:

• Collector current (I_C) = 10 mA
• Base current (I_B) = 100 μA = 0.1 mA

Calculate β (Common Emitter Current Gain):

• β = I_C / I_B
• β = 10 mA / 0.1 mA
• β = 100

Calculate α (Common Base Current Gain):

• I_E = I_C + I_B = 10 mA + 0.1 mA = 10.1 mA
• α = I_C / I_E
• α = 10 mA / 10.1 mA
• α = 0.990 or 0.99

Relation between α and β:

• α = β / (β + 1)
• α = 100 / (100 + 1) = 100 / 101 = 0.990
• β = α / (1 - α)
• β = 0.99 / (1 - 0.99) = 0.99 / 0.01 = 99 ≈ 100

Mnemonic: “ABC” - “Alpha equals Beta divided by (Beta plus one) for Current gains”

Question 5(c) [7 marks]

#

Discuss Strategies of electronic waste management in the small electronics Industries.

Answer:

E-Waste Management Strategies for Small Electronics Industries:

Key Implementation Steps:

• Inventory Management: Track electronic components throughout lifecycle
• Authorized Partnerships: Work only with certified e-waste handlers
• Documentation: Maintain records of waste disposal for compliance
• Green Design: Design products for easy disassembly and recycling

Regulatory Compliance:

• Registration: Register with pollution control board
• Authorization: Obtain necessary permits
• Annual Returns: Submit regular compliance reports

Diagram:

graph TD
    A[E-Waste Management] --> B[Collection & Segregation]
    A --> C[Storage]
    A --> D[Transportation]
    A --> E[Processing]
    B --> F[Separate bins for different components]
    C --> G[Safe storage in designated areas]
    D --> H[Authorized carriers only]
    E --> I[Authorized recyclers]
    E --> J[Material recovery]
    E --> K[Safe disposal of residues]

Mnemonic: “SRRTA” - “Segregate, Reduce, Reuse, Train, Authorize”

Question 5(a) [3 marks] (OR)

#

Draw CB, CE and CC transistor configuration circuits.

Answer:

Transistor Configuration Circuits:

Key Characteristics:

• CB: High stability, low input impedance, high output impedance
• CE: Medium stability, medium input impedance, medium output impedance
• CC: Low stability, high input impedance, low output impedance

Mnemonic: “EBC” - “Emitter input for CB, Base input for CE/CC, Collector output for CB/CE”

Question 5(b) [4 marks] (OR)

#

Derive relation between current gains α and β.

Answer:

Relation Between Current Gains α and β:

Given definitions:

• α = I_C/I_E (Common Base current gain)
• β = I_C/I_B (Common Emitter current gain)

Step 1: Use current relation in transistor

• I_E = I_C + I_B

Step 2: Express α in terms of β

• α = I_C/I_E
• α = I_C/(I_C + I_B)

Step 3: Substitute I_B = I_C/β

• α = I_C/(I_C + I_C/β)
• α = I_C/(I_C(1 + 1/β))
• α = I_C/(I_C(β + 1)/β)
• α = β/(β + 1)

Step 4: Express β in terms of α

• β = α/(1 - α)

Diagram:

Mnemonic: “ABR” - “Alpha = Beta divided by (Beta plus one) Reciprocally”

Question 5(c) [7 marks] (OR)

#

Define E-Waste and Explain disposal of electronic waste.

Answer:

E-Waste Definition: Electronic waste (e-waste) refers to discarded electrical or electronic devices that have reached end-of-life or become obsolete, including computers, televisions, mobile phones, printers, and other electronic equipment containing hazardous components like lead, mercury, cadmium, PCBs, and brominated flame retardants.

Disposal Methods of E-Waste:

Disposal Process Flow:

• Initial Assessment: Determine if device can be repaired/reused
• Data Sanitization: Secure erasure of personal/business data
• Disassembly: Separation into component categories
• Resource Recovery: Extraction of valuable materials
• Hazardous Waste: Special handling of toxic components

Diagram:

graph TD
    A[E-Waste Disposal] --> B[Collection]
    B --> C[Sorting & Segregation]
    C --> D[Recycling]
    C --> E[Recovery]
    C --> F[Safe Disposal]
    D --> G[Disassembly]
    G --> H[Material Sorting]
    H --> I[Crushing & Shredding]
    I --> J[Material Separation]
    J --> K[Refinement]
    K --> L[New Products]
    F --> M[Landfill for Inert Material]
    F --> N[Incineration with Pollution Control]

Mnemonic: “CRESD” - “Collect, Recycle, Extract, Separate, Dispose”