Elements of Electrical & Electronics Engineering (1313202) - Winter 2024 Solution

Question 1(a) [3 marks]

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Explain difference between Active and passive network.

Answer:

Mnemonic: “Active Adds Power, Passive Parts Take”

Question 1(b) [4 marks]

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State and explain Kirchhoff’s voltage law (KVL).

Answer:

Kirchhoff’s Voltage Law (KVL) states that the algebraic sum of all voltages around any closed loop in a circuit is zero.

Diagram:

graph LR
    A((A)) -- V1 --> B((B))
    B -- V2 --> C((C))
    C -- V3 --> D((D))
    D -- V4 --> A

Mathematically: V1 + V2 + V3 + V4 = 0

• Voltage drops: When passing through a resistor in direction of current, voltage is negative
• Voltage rises: When passing through a source from negative to positive, voltage is positive

Mnemonic: “Voltage Loop Equals Zero”

Question 1(c) [7 marks]

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Define the following terms: (1) Charge (2) Current (3) Potential (4) E.M.F. (5) Inductance (6) Capacitance (7) Frequency.

Answer:

Mnemonic: “Coulombs’ Flow Pressurized by Energy Induces Capacitive Fluctuations”

Question 1(c) OR [7 marks]

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State Ohm’s law. Write its application and limitation.

Answer:

Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference and inversely proportional to the resistance.

Diagram:

V = I × R

Where:

• V = Voltage (volts)
• I = Current (amperes)
• R = Resistance (ohms)

Applications:

• Circuit design and analysis
• Power consumption calculations
• Component value determination
• Voltage divider networks
• Current divider networks

Limitations:

• Valid only for linear components
• Not applicable to non-ohmic devices (diodes, transistors)
• Invalid at high temperatures
• Not valid for semiconductors
• Cannot be applied to non-linear resistive elements

Mnemonic: “Volts Reveal Amps’ Motion”

Question 2(a) [3 marks]

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Draw and explain energy band diagrams for insulator, conductor and Semiconductor.

Answer:

Diagram:

graph TD
    subgraph Conductor
    A1[Conduction Band] --- B1[Overlapping]
    B1 --- C1[Valence Band]
    end
    subgraph Semiconductor
    A2[Conduction Band] --- B2[Small Eg]
    B2 --- C2[Valence Band]
    end
    subgraph Insulator
    A3[Conduction Band] --- B3[Large Eg]
    B3 --- C3[Valence Band]
    end

• Conductor: Valence and conduction bands overlap, allowing free electron movement
• Semiconductor: Small energy gap (0.7-3 eV) between bands allows limited conduction
• Insulator: Large energy gap (>3 eV) prevents electrons from moving to conduction band

Mnemonic: “Conductors Overlap, Semiconductors Jump Small, Insulators Block All”

Question 2(b) [4 marks]

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Write statement of Maximum power transfer theorem and reciprocity theorem.

Answer:

Mnemonic: “Match Resistance for Maximum Power; Swap Sources, Current Stays”

Question 2(c) [7 marks]

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Explain the formation and conduction of N-type materials.

Answer:

Diagram:

graph TD
    A[Silicon/Germanium] -- "Add Pentavalent Impurity
(P, As, Sb)" --> B[N-type Semiconductor]
    B --> C[Extra Electron in Crystal]
    C --> D[Majority Carriers: Electrons]
    C --> E[Minority Carriers: Holes]

• Formation Process:

  • Pure silicon/germanium doped with pentavalent impurity atoms (P, As, Sb)
  • Impurity atoms have 5 valence electrons (silicon has 4)
  • Four electrons form covalent bonds, fifth becomes free electron
  • Creates excess negative charge carriers

• Conduction Mechanism:

  • Majority carriers: Electrons
  • Minority carriers: Holes
  • Electron movement provides electrical conduction
  • Even at room temperature, free electrons enable current flow

Mnemonic: “Pentavalent Provides Plus-One Electron”

Question 2(a) OR [3 marks]

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Define valence band, conduction band and forbidden gap.

Answer:

Mnemonic: “Valence Binds, Conduction Flows, Forbidden Gaps Block”

Question 2(b) OR [4 marks]

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Define the terms active power, reactive power and power factor with power triangle.

Answer:

Diagram:

• Active Power (P): Actual power consumed, measured in watts (W), P = VI cosθ
• Reactive Power (Q): Power oscillating between source and load, measured in volt-amperes reactive (VAR), Q = VI sinθ
• Power Factor: Ratio of active power to apparent power, PF = cosθ = P/S

Mnemonic: “Real Power Works, Reactive Power Waits”

Question 2(c) OR [7 marks]

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Explain the structure of atom of trivalent, tetravalent and pentavalent elements.

Answer:

Diagram:

graph TD
    subgraph Trivalent
    A[3 Valence Electrons] --> B[Examples: B, Al, Ga]
    end
    subgraph Tetravalent
    C[4 Valence Electrons] --> D[Examples: Si, Ge, C]
    end
    subgraph Pentavalent
    E[5 Valence Electrons] --> F[Examples: P, As, Sb]
    end

Mnemonic: “Three Accepts, Four Forms, Five Donates”

Question 3(a) [3 marks]

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Draw the symbol of photodiode and state its application.

Answer:

Diagram:

Applications of Photodiode:

• Light sensors and detectors
• Optical communication systems
• Solar cells and photovoltaic applications
• Camera exposure controls
• Medical equipment (pulse oximeters)

Mnemonic: “Light Triggers Electric Current”

Question 3(b) [4 marks]

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Write a Short note on LED.

Answer:

Diagram:

• Structure: P-N junction diode that emits light when forward biased
• Working Principle: Electron-hole recombination releases energy as photons
• Types: Various colors based on semiconductor material (GaAs, GaP, GaN)
• Advantages: Low power consumption, long life, small size, fast switching
• Applications: Displays, indicators, lighting, remote controls, optical communications

Mnemonic: “Electrons Jump, Photons Emit”

Question 3(c) [7 marks]

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Draw and explain VI characteristic of PN junction diode.

Answer:

Diagram:

P-N Junction Diode V-I Characteristics:

• Forward Bias Region:

  • Diode conducts when voltage exceeds knee/cut-in voltage (0.3V for Ge, 0.7V for Si)
  • Current increases exponentially with voltage
  • Low resistance state

• Reverse Bias Region:

  • Very small leakage current flows
  • Current remains almost constant with increasing reverse voltage
  • High resistance state
  • Breakdown occurs at high reverse voltage

• Key Points:

  • Non-linear device
  • Unidirectional current flow
  • Temperature dependent

Mnemonic: “Forward Flows Freely, Reverse Resists Rigidly”

Question 3(a) OR [3 marks]

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List the applications of PN junction diode.

Answer:

Applications of PN Junction Diode:

• Rectification in power supplies
• Signal demodulation
• Logic gates in digital circuits
• Voltage regulation (with zener diodes)
• Signal clipping and clamping circuits
• Protection circuits against reverse polarity

Mnemonic: “Rectify, Detect, Clip, Protect”

Question 3(b) OR [4 marks]

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Explain the formation of depletion region in unbiased P-N junction.

Answer:

Diagram:

graph LR
    A[P-type] --- B[Depletion
Region] --- C[N-type]
    D[+] --- B --- E[-]

• Formation Process:

  • Electrons from N-side diffuse into P-side
  • Holes from P-side diffuse into N-side
  • Recombination occurs at junction
  • Immobile ions remain (positive in N-side, negative in P-side)
  • Electric field develops, opposing further diffusion
  • Equilibrium is established, creating depletion region

• Characteristics:

  • Free of charge carriers
  • Acts as insulator/barrier
  • Creates built-in potential

Mnemonic: “Diffusion Creates Barrier Field”

Question 3(c) OR [7 marks]

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Explain construction, working and applications of PN junction diode.

Answer:

Diagram:

graph LR
    A[P-type] --- B[Junction] --- C[N-type]
    D[Anode] --- A
    C --- E[Cathode]

Construction:

• P-type semiconductor joined with N-type semiconductor
• Made from single crystal of silicon or germanium
• Metal contacts connected to P and N regions

Working:

• Forward Bias:

  • Positive to P, negative to N
  • Depletion region narrows
  • Current flows when voltage exceeds barrier potential

• Reverse Bias:

  • Positive to N, negative to P
  • Depletion region widens
  • Only small leakage current flows

Applications:

• Power rectification
• Signal detection
• Voltage regulation
• Switching applications
• Protection circuits
• Logic gates

Mnemonic: “Join P-N, Control Current Direction”

Question 4(a) [3 marks]

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Define: (1) Ripple frequency (2) Ripple factor (3) PIV of a diode.

Answer:

Mnemonic: “Frequency Fluctuates, Factor Measures, PIV Protects”

Question 4(b) [4 marks]

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Give comparison between full wave rectifier with two diodes and full wave bridge rectifier.

Answer:

Mnemonic: “Two Diodes Tap Center, Four Make Bridge”

Question 4(c) [7 marks]

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Explain zener diode as voltage regulator.

Answer:

Diagram:

Working Principle:

• Zener diode operates in reverse breakdown region
• Maintains constant voltage across its terminals
• Acts as voltage reference

Circuit Operation:

• Series resistor Rs limits current
• Zener conducts when input exceeds breakdown voltage
• Excess current flows through zener diode
• Output voltage remains constant at zener voltage

Advantages:

• Simple circuit
• Low cost
• Good regulation for small load changes

Limitations:

• Power dissipation in zener and series resistor
• Limited current capability
• Temperature dependency

Mnemonic: “Zener Breaks Down to Hold Voltage Steady”

Question 4(a) OR [3 marks]

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What is rectifier? Explain full wave rectifier with waveforms.

Answer:

Rectifier: A circuit that converts AC voltage to pulsating DC voltage.

Diagram:

Waveforms:

Mnemonic: “Both Half-Cycles Become Positive”

Question 4(b) OR [4 marks]

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Why filter is required in rectifier? State the different types of filter and explain any one type of filter.

Answer:

Need for Filter:

• Rectifier output contains AC ripple component
• Pure DC required for electronic circuits
• Filters smooth pulsating DC by removing AC components

Types of Filters:

• Capacitor filter (C-filter)
• Inductor filter (L-filter)
• LC filter
• π (Pi) filter
• CLC filter

Capacitor Filter:

graph LR
    A[AC Input] --> B[Rectifier] --> C[Capacitor Filter] --> D[DC Output]

Working:

• Capacitor charges during voltage rise
• Discharges slowly during voltage fall
• Provides current when input decreases
• Reduces ripple voltage

Advantages:

• Simple and inexpensive
• Effective for light loads
• Reduces ripple significantly

Mnemonic: “Capacitor Catches Peaks, Releases Slowly”

Question 4(c) OR [7 marks]

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Write the need of rectifier. Explain bridge rectifier with circuit diagram and draw its input and output waveforms.

Answer:

Need of Rectifier:

• Convert AC to DC for electronic devices
• Most electronic circuits require DC power
• Batteries provide DC but AC is distributed
• Building block of power supplies
• Essential for charging systems

Bridge Rectifier Circuit:

Input Waveform:

Output Waveform:

Working:

• During positive half cycle: D1 and D4 conduct
• During negative half cycle: D2 and D3 conduct
• Load receives unidirectional current in both cycles
• Utilizes both halves of input waveform

Mnemonic: “Four Diodes Direct All Current One Way”

Question 5(a) [3 marks]

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Explain causes of electronic waste.

Answer:

Causes of Electronic Waste:

• Rapid technological advancement
• Planned obsolescence of products
• Decreasing product lifespan
• Consumer behavior preferring new devices
• Limited repair options for electronics
• High repair costs compared to replacement

Mnemonic: “Technology Advances, Products Expire Rapidly”

Question 5(b) [4 marks]

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Compare PNP and NPN transistors.

Answer:

Parameter	PNP Transistor	NPN Transistor
Symbol
Majority Carriers	Holes	Electrons
Current Flow	Emitter to Collector	Collector to Emitter
Biasing	Emitter more positive than Base	Base more positive than Emitter
Switching Speed	Slower	Faster
Applications	Low frequency, high current	High frequency, switching

Diagram:

Mnemonic: “Negative-Positive-Negative vs Positive-Negative-Positive”

Question 5(c) [7 marks]

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Draw the symbol, explain the construction and working of MOSFET.

Answer:

Symbol:

Construction:

graph TD
    A[Metal Gate] --- B[Silicon Dioxide Insulator]
    B --- C[N-type Channel]
    C --- D[P-type Substrate]
    E[Source] --- C
    C --- F[Drain]

Working Principle:

• Enhancement Mode N-Channel MOSFET:

  • No channel exists without gate voltage
  • Positive gate voltage attracts electrons from substrate
  • Induced channel allows current flow from drain to source
  • Increasing gate voltage enhances conductivity

• Key Features:

  • Voltage-controlled device (high input impedance)
  • No gate current required (unlike BJT)
  • Faster switching than BJT
  • Lower power dissipation

Applications:

• Digital logic circuits
• Switching applications
• Amplifiers
• Power control devices

Mnemonic: “Gate Voltage Creates Electron Channel”

Question 5(a) OR [3 marks]

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Explain methods to handle electronic waste.

Answer:

Methods to Handle Electronic Waste:

Mnemonic: “Reduce, Reuse, Recycle, Regulate, Recover”

Question 5(b) OR [4 marks]

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Derive the relationship between αdc and βdc.

Answer:

Diagram:

Transistor Current Relationships:

• IE = IC + IB (Current entering equals current leaving)
• αdc = IC/IE (Common Base current gain)
• βdc = IC/IB (Common Emitter current gain)

Derivation:

• From IE = IC + IB
• Divide both sides by IC: IE/IC = 1 + IB/IC
• Therefore: 1/αdc = 1 + 1/βdc
• Solving for βdc: βdc = αdc/(1-αdc)
• And for αdc: αdc = βdc/(1+βdc)

Table of Values:

Mnemonic: “Alpha-Beta Relate as αdc = βdc/(1+βdc)”

Question 5(c) OR [7 marks]

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Explain common collector configuration with its input and output characteristics.

Answer:

Common Collector Circuit (Emitter Follower):

Input Characteristics: (IB vs VBE)

Output Characteristics: (IE vs VCE)

Key Features:

• Voltage gain ≈ 1 (slightly less)
• High current gain (β+1)
• High input impedance
• Low output impedance
• No phase inversion between input and output
• Used as buffer/impedance matching circuit

Mnemonic: “Emitter Follows Base Voltage”