Fundamentals of Electronics (4311102) - Summer 2023 Solution

Question 1(a) [3 marks]

#

Define Active and Passive components.

Answer:

Mnemonic: “APE” - Active needs Power to Enhance signals

Question 1(b) [4 marks]

#

State types of capacitors based on materials used.

Answer:

Table: Types of Capacitors Based on Materials

Mnemonic: “CEPPMG” - Ceramic Electrolytic Paper Plastic Mica Glass

Question 1(c) [7 marks]

#

Explain resistor color coding technique with example.

Answer:

The resistor color code uses colored bands to indicate resistance value, tolerance, and reliability.

Table: Standard Resistor Color Code

Example 1: Red-Violet-Orange-Gold

• 1st band (Red) = 2
• 2nd band (Violet) = 7
• 3rd band (Orange) = ×1,000
• 4th band (Gold) = ±5% tolerance
• Value: 27 × 1,000 = 27,000Ω = 27kΩ ±5%

Example 2: Brown-Black-Yellow-Silver

• 1st band (Brown) = 1
• 2nd band (Black) = 0
• 3rd band (Yellow) = ×10,000
• 4th band (Silver) = ±10% tolerance
• Value: 10 × 10,000 = 100,000Ω = 100kΩ ±10%

flowchart LR
    A[1st Band
First Digit] --> B[2nd Band
Second Digit]
    B --> C[3rd Band
Multiplier]
    C --> D[4th Band
Tolerance]
    style A fill:#f96,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#f90,stroke:#333
    style D fill:#fc0,stroke:#333

Mnemonic: “BBROY Great Britain Very Good Wife” for colors 0-9 (Black Brown Red Orange Yellow Green Blue Violet Gray White)

Question 1(c) OR [7 marks]

#

Explain construction, working Characteristic and application of LDR.

Answer:

Light Dependent Resistor (LDR)

graph TD
    A[More Light] -->|Releases electrons| B[More Free Electrons]
    B --> C[Lower Resistance]
    D[Less Light] -->|Fewer electrons released| E[Fewer Free Electrons]
    E --> F[Higher Resistance]

Mnemonic: “MOLD” - More light On, Less resistance Down

Question 2(a) [3 marks]

#

Classify Resistors based on materials.

Answer:

Table: Resistor Classification Based on Materials

Mnemonic: “CMMWTF” - Carbon Makes Much Wire To Form resistors

Question 2(b) [4 marks]

#

Calculate value of resistor for a given color code. – (i) Brown, Black, Yellow, Golden (ii) Yellow, Violet, Red, Silver

Answer:

Part (i): Brown, Black, Yellow, Golden

• 1st Band (Brown) = 1
• 2nd Band (Black) = 0
• 3rd Band (Yellow) = ×10,000
• 4th Band (Golden) = ±5% tolerance

Calculation: Value = 10 × 10,000 = 100,000Ω = 100kΩ ±5%

Part (ii): Yellow, Violet, Red, Silver

• 1st Band (Yellow) = 4
• 2nd Band (Violet) = 7
• 3rd Band (Red) = ×100
• 4th Band (Silver) = ±10% tolerance

Calculation: Value = 47 × 100 = 4,700Ω = 4.7kΩ ±10%

Mnemonic: “BBROY Great Britain Very Good Wife” for the color sequence 0-9

Question 2(c) [7 marks]

#

Illustrate construction and operation of Electrolytic capacitors.

Answer:

Electrolytic Capacitor Construction and Operation

Operation Principle:

1. The oxide layer on the anode acts as an extremely thin dielectric
2. The large surface area and thin dielectric create high capacitance
3. When connected to DC voltage (with correct polarity), charges accumulate
4. Positive plate (+) attracts negative charges; negative plate (-) attracts positive charges

graph TD
    A[Aluminum Foil
Anode] --> B[Oxide Layer
Dielectric]
    B --> C[Electrolyte
Cathode]
    C --> D[Aluminum Foil
Terminal Connection]
    style A fill:#fc9,stroke:#333
    style B fill:#9cf,stroke:#333
    style C fill:#cfc,stroke:#333
    style D fill:#fc9,stroke:#333

Key Characteristics:

• Polarity: Must be connected correctly (+/-)
• High capacitance: 1μF to thousands of μF
• Voltage limitations: Breakdown if exceeded
• Leakage current: Higher than other capacitor types

Mnemonic: “PAVE” - Polarized Aluminum with Very high capacitance and Electrolyte

Question 2(a) OR [3 marks]

#

State the importance of filter circuit in rectifier.

Answer:

Importance of Filter Circuit in Rectifier

Mnemonic: “SVRL” - Smoothens Voltage by Reducing ripples for Load

Question 2(b) OR [4 marks]

#

Differentiate between P type semiconductor and N type semiconductor.

Answer:

Table: P-type vs N-type Semiconductor

Mnemonic: “HELP-NED” - Holes Exist in Large quantities in P-type, Negative Electrons Dominate N-type

Question 2(c) OR [7 marks]

#

Illustrate working of Bridge Rectifier with waveforms.

Answer:

Bridge Rectifier Working Principle

Working in Positive Half Cycle:

• Diodes D1 and D3 conduct
• Diodes D2 and D4 are reverse biased (off)
• Current flows: AC+ → D1 → Load → D3 → AC-

Working in Negative Half Cycle:

• Diodes D2 and D4 conduct
• Diodes D1 and D3 are reverse biased (off)
• Current flows: AC- → D2 → Load → D4 → AC+

graph TD
    AC[AC Input] --> D1[D1]
    AC --> D3[D3]
    D1 --> Load[Load]
    D3 --> Load
    Load --> D2[D2]
    Load --> D4[D4]
    D2 --> AC
    D4 --> AC
    style AC fill:#fcf,stroke:#333
    style Load fill:#cfc,stroke:#333
    style D1 fill:#9cf,stroke:#333
    style D2 fill:#9cf,stroke:#333
    style D3 fill:#9cf,stroke:#333
    style D4 fill:#9cf,stroke:#333

Waveforms:

AC Input:      _/\      _/\      _/\      
              /    \   /    \   /    \   
    0 ______/      \_/      \_/      \__
             \    /   \    /   \    /
              \__/     \__/     \__/


DC Output:     _       _       _      
              / \     / \     / \     
    0 ______/   \___/   \___/   \_____

Advantages:

• Utilizes both half cycles of AC input
• Higher output voltage and efficiency compared to half-wave
• No center-tapped transformer required

Mnemonic: “FBRO” - Four diodes, Both cycles, Rectified Output

Question 3(a) [3 marks]

#

Define (1) PIV (2) Ripple Factor.

Answer:

Formula: Ripple Factor (r) = V₍ᵣₘₛ₎ₐ.ₖ / V₍ᵈᶜ₎

Mnemonic: “PIR” - Peak Inverse voltage Restricts, Ripple indicates Rectification quality

Question 3(b) [4 marks]

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Illustrate VI characteristics of PN junction diode.

Answer:

V-I Characteristics of PN Junction Diode

         Current (I)
             ↑
             |              /
             |             /
             |            /
             |           /
             |          /
    ---------|--------/-----→ Voltage (V)
             |    0.7V
             |/
     ________|________________________
             |
             | Small leakage current
             |
             |        Breakdown
             |           ↓
             |           |
             |           |

Key Points:

• Forward threshold: ~0.7V for Si, ~0.3V for Ge
• Forward region: High conductivity
• Reverse region: Very high resistance
• Breakdown region: Sudden increase in reverse current

Mnemonic: “FBRL” - Forward Bias Resists Little, reverse blocks lots

Question 3(c) [7 marks]

#

Explain the working of capacitor input and choke input filter with waveforms.

Answer:

1. Capacitor Input Filter

Advantages:

• Higher DC output voltage
• Simple and economical
• Good ripple reduction

Limitations:

• Poor voltage regulation
• High peak diode currents
• Suitable for low current applications

2. Choke Input Filter

Advantages:

• Better voltage regulation
• Lower peak diode currents
• Suitable for high current applications

Limitations:

• Lower DC output voltage
• More expensive
• Bulkier than capacitor filter

graph LR
    A[Rectifier Output] --> B[Capacitor/Choke Input]
    B --> C[Filtered Output]
    style A fill:#f96,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#6f9,stroke:#333

Waveform Comparison:

Rectifier output:     __      __      __
                     /  \    /  \    /  \
                    /    \  /    \  /    \
           0 ______/      \/      \/      \____

Capacitor filter:    ___     ___     ___
                     \  \    \  \    \  \
                      \  \    \  \    \  \
           0 _________\__\____\__\____\__\____

Choke filter:         __________ __________
                     /          /
                    /          /
           0 ______/          /____________

Mnemonic: “VOICE” - Voltage Output Is Constant with Either filter, but choke gives better regulation

Question 3(a) OR [3 marks]

#

State the function and importance of Zener diode.

Answer:

Function and Importance of Zener Diode

Mnemonic: “VPRVW” - Voltage Protection, Regulation, and Voltage Waveform control

Question 3(b) OR [4 marks]

#

Describe Light emitting diode (LED) with its characteristic.

Answer:

Light Emitting Diode (LED) Characteristics

graph LR
    A[Voltage Applied] -->|Forward Bias| B[Electron-Hole Recombination]
    B --> C[Energy Released]
    C --> D[Light Emission]
    style A fill:#f96,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#fc9,stroke:#333
    style D fill:#6f9,stroke:#333

Mnemonic: “CRAVE” - Current Regulated And Voltage Emits light

Question 3(c) OR [7 marks]

#

Illustrate the working of capacitor input and choke input filter.

Answer:

Capacitor Input Filter:

Circuit Diagram:

    +------|>|------+
    |      D1       |
AC  |               | Load
In  |               | RL    +
    +------|<|------+-----||---+
    |      D2       |     C    |
    +---------------+----------+

Choke Input Filter:

Circuit Diagram:

    +------|>|------+
    |      D1       |
AC  |               +----LLLLL----+
In  |                     L       |
    +------|<|------+          RL +
    |      D2       |     C       |
    +---------------+----||-------+

Comparison:

Mnemonic: “CHEER” - Capacitor Holds Energy, inductor Ensures Regulated current

Question 4(a) [3 marks]

#

Discuss characteristics of PN junction diode.

Answer:

Characteristics of PN Junction Diode

Mnemonic: “FRBCT” - Forward conducts, Reverse blocks, Breakdown destroys, Capacitance changes, Temperature affects

Question 4(b) [4 marks]

#

Compare between P-N junction diode and Zener diode.

Answer:

Table: P-N Junction Diode vs. Zener Diode

Mnemonic: “FORBAR” - Forward Operation is Regular, Breakdown Application is the Real difference

Question 4(c) [7 marks]

#

Illustrate the function of Zener diode as a voltage regulator.

Answer:

Zener Diode as Voltage Regulator

Working Principle:

1. Zener diode is connected in reverse bias
2. When input voltage rises above Zener voltage, diode conducts
3. Excess voltage is dropped across series resistor
4. Output voltage remains constant at Zener voltage

graph LR
    A[Input Voltage] --> B[Series Resistor]
    B --> C[Output Voltage]
    C --> D[Load]
    C --> E[Zener Diode]
    E --> F[Ground]
    style A fill:#f96,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#6f9,stroke:#333
    style D fill:#fc9,stroke:#333
    style E fill:#f9f,stroke:#333

Circuit Diagram:

     +----[Rs]----+----+
     |            |    |
Vin  |            +   RL   Vout = Vz
     |            |    |
     +--------|>|--+----+
              Zener

Regulation Cases:

Limitations:

• Power dissipation in Zener and Rs
• Minimum input voltage requirement (Vin > Vz + Voltage drop across Rs)
• Limited current capability

Mnemonic: “VISOR” - Voltage In Stays Out Regulated

Question 4(a) OR [3 marks]

#

Discuss transistor in brief.

Answer:

Transistor Overview

Mnemonic: “TAWAI” - Transistors Amplify, Work As switches, and are Integral to electronics

Question 4(b) OR [4 marks]

#

Derive relation between α and β for transistor amplifier.

Answer:

Relation Between α and β

Derivation Steps:

1. We know that emitter current is the sum of base and collector currents: I_E = I_B + I_C

2. Alpha definition: α = I_C/I_E

3. Beta definition: β = I_C/I_B

4. From step 1, we can write: I_B = I_E - I_C

5. Substituting into beta definition: β = I_C/(I_E - I_C)

6. Using alpha definition, I_C = α × I_E: β = (α × I_E)/(I_E - α × I_E)

7. Simplifying: β = α/(1 - α)

8. Conversely, we can also express α in terms of β: α = β/(β + 1)

Relationship Table:

Mnemonic: “ABR” - Alpha and Beta are Related by α = β/(β+1) or β = α/(1-α)

Question 4(c) OR [7 marks]

#

Explain in detail the construction of NPN and PNP transistor.

Answer:

Construction of NPN and PNP Transistors

NPN Transistor Construction:

    Emitter (N)   Base (P)   Collector (N)
       |            |            |
       v            v            v
    +------+     +---+     +----------+
    |  N+  |     | P |     |    N     |
    +------+     +---+     +----------+
       |           |           |
       |           |           |
       E           B           C

PNP Transistor Construction:

    Emitter (P)   Base (N)   Collector (P)
       |            |            |
       v            v            v
    +------+     +---+     +----------+
    |  P+  |     | N |     |    P     |
    +------+     +---+     +----------+
       |           |           |
       |           |           |
       E           B           C

Manufacturing Process:

1. Start with semiconductor substrate (N or P type)
2. Create layers through epitaxial growth
3. Form junctions through diffusion or ion implantation
4. Add metal contacts for terminals
5. Package in protective case

graph TD
    A[Silicon Wafer] --> B[Epitaxial Layer Growth]
    B --> C[Diffusion of Dopants]
    C --> D[Oxide Insulation]
    D --> E[Metallization]
    E --> F[Packaging]
    style A fill:#fc9,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#f9f,stroke:#333
    style D fill:#cfc,stroke:#333
    style E fill:#f96,stroke:#333
    style F fill:#9cf,stroke:#333

Mnemonic: “ENB-CPM” - Emitter has N in NPN, Collector is Proportionally Medium-doped

Question 5(a) [3 marks]

#

Explain e-waste in brief.

Answer:

Electronic Waste (E-Waste)

Mnemonic: “TECH” - Toxic Electronics Create Hazards when improperly disposed

Question 5(b) [4 marks]

#

Illustrate operation of NPN transistor with figure.

Answer:

NPN Transistor Operation

Symbol and Basic Operation:

      Collector (C)
          |
          |
          v
    +-----+-----+
    |     |     |
    |    / \    |
Base |---|   |---| Collector
(B)  |    \ /    |
    |     |     |
    +-----+-----+
          |
          |
          v
       Emitter (E)

Basic Operating Principle:

• Base-Emitter junction is forward biased
• Base-Collector junction is reverse biased
• Small base current controls larger collector current

graph TD
    A[Base Current Injected] --> B[Electrons from Emitter Enter Base]
    B --> C[Most Electrons Reach Collector]
    C --> D[Small Change in Base Current Controls Larger Collector Current]
    style A fill:#f96,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#f9f,stroke:#333
    style D fill:#cfc,stroke:#333

Current Flow in NPN Transistor:

• Electrons flow from emitter to collector
• Small base current controls larger collector current
• Amplification factor (β) = I_C/I_B

Mnemonic: “BECAN” - Base current Enables Collector-to-emitter current Amplification in NPN

Question 5(c) [7 marks]

#

Illustrate common emitter (CE) configuration of Transistor with input and output characteristics.

Answer:

Common Emitter (CE) Configuration

Circuit Diagram:

                  +Vcc
                    |
                    |
                   RL
                    |
                    |
    +-----+    +---o--- Vout
    |     |    |   |
Vin o-----o----|B  C
    |     |    |   |
    RB    |    |   |
    |     |    |E  |
    |     |    |   |
    +-----+----+---o--- GND
                    |
                   RE
                    |
                    +

Input Characteristics:

• Plots I_B vs V_BE for different V_CE values
• Resembles forward-biased diode characteristic
• Threshold voltage ~0.7V for silicon transistors

    IB (μA)
      ↑
      |                /
      |               /
      |              /
      |             /
      |            /
      |           /
      |          /
      |         /
    --|--------/---------------→ VBE (V)
      |     0.7V

Output Characteristics:

• Plots I_C vs V_CE for different I_B values
• Shows three regions: Active, Saturation, Cutoff

    IC (mA)
      ↑
      |                 ________ IB = 50μA
      |                /
      |               /________ IB = 40μA
      |              /
      |             /_________ IB = 30μA
      |            /
      |           /__________ IB = 20μA
      |          /
      |         /____________ IB = 10μA
      |        /
      |       /
    --|------/-------------------→ VCE (V)
      |  Saturation│  Active
      |  Region    │  Region

Characteristics:

• Current gain (β) = I_C/I_B (typically 50-200)
• Input resistance: 1-2 kΩ
• Output resistance: 40-50 kΩ
• Phase shift: 180° between input and output

Mnemonic: “CASIO” - Common emitter Amplifies Signals with Inverted Output

Question 5(a) OR [3 marks]

#

State types of e-waste.

Answer:

Types of Electronic Waste (E-Waste)

Mnemonic: “CLIMATE” - Computing, Lighting, Industrial, Medical, Appliances, Telecommunications, Electronic components

Question 5(b) OR [4 marks]

#

Illustrate different categories of Electronics waste.

Answer:

Categories of Electronic Waste

pie
    title "Typical E-Waste Composition by Category"
    "IT & Telecom" : 25
    "Large Appliances" : 29
    "Small Appliances" : 14
    "Consumer Electronics" : 17
    "Lighting" : 5
    "Other Categories" : 10

Mnemonic: “LIMCEST” - Large appliances, IT equipment, Medical devices, Consumer electronics, Electronic tools, Small appliances, Telecom equipment

Question 5(c) OR [7 marks]

#

Explain transistor as a switch in cutoff and saturation region.

Answer:

Transistor as a Switch

Circuit Diagram:

                  +Vcc
                    |
                    |
                    R
                    |
                    |
                    C
           +--------+--------+
           |                 |
Input o----+----[RB]----+B  |
           |        |E  |    |
           |        |   |    |
           +--------+---+----o Output
                    |
                    |
                   GND

Cutoff Operation (OFF State):

• Input voltage is below 0.7V (typically 0V)
• Base-emitter junction is not forward biased
• No base current flows (I_B ≈ 0)
• No collector current flows (I_C ≈ 0)
• Collector-emitter voltage is approximately V_CC
• Transistor acts as an open switch

Saturation Operation (ON State):

• Input voltage is above 0.7V
• Base-emitter junction is forward biased
• Sufficient base current flows (I_B > I_C/β)
• Collector current reaches maximum (I_C(sat))
• Collector-emitter voltage drops to minimum (V_CE(sat) ≈ 0.2V)
• Transistor acts as a closed switch

graph LR
    A[Input Signal] --> B{Voltage Level?}
    B -->|V < 0.7V| C[Cutoff Region
Switch OFF]
    B -->|V > 0.7V| D[Saturation Region
Switch ON]
    C --> E[High V_CE
No Current]
    D --> F[Low V_CE
Maximum Current]
    style A fill:#f96,stroke:#333
    style B fill:#69f,stroke:#333
    style C fill:#f9f,stroke:#333
    style D fill:#cfc,stroke:#333
    style E fill:#9cf,stroke:#333
    style F fill:#fc9,stroke:#333

Applications:

• Digital logic circuits
• Relay and motor drivers
• LED and lamp control
• Power converters
• Signal conditioning

Key Design Considerations:

• Base resistor (R_B) limits base current
• Collector resistor (R_C) limits collector current
• Saturation requires I_B > I_C/β for reliable switching
• Fast switching requires consideration of charge storage effects

Mnemonic: “COSVL” - Cutoff means Off State with Vce Large, saturation means low Vce