Question 1(a) [3 marks]

Give the difference between Passive components and Active components

Answer:

Passive Components	Active Components
Do not require external power source	Require external power source to operate
Cannot amplify or process signals	Can amplify, switch or process signals
Examples: Resistors, Capacitors, Inductors	Examples: Transistors, Diodes, ICs
Cannot control current flow by another signal	Can control current flow using another signal
Store or dissipate energy	Generate energy or provide gain

Mnemonic: "PAPER-A" - Passive Are Power-free, Energy-storing/Resistive; Active Are Amplifying

Question 1(b) [4 marks]

Explain Working of Light dependent resistor with neat diagram.

Answer:

graph LR
    A[Light] --> B[LDR]
    B --> C[Change in Resistance]
    style A fill:#lightblue
    style B fill:#lightgreen
    style C fill:#lightpink

Working of LDR:

Construction: LDR consists of a semiconductor material (typically cadmium sulfide) with high resistance in darkness
Photoconductivity: When light falls on the surface, photons transfer energy to electrons, creating free electron-hole pairs
Resistance variation: Resistance decreases dramatically as light intensity increases - from megaohms in darkness to few hundred ohms in bright light
Applications: Used in light sensing circuits, automatic street lights, camera exposure control

Mnemonic: "MILD" - More Illumination, Less resistance in Devices

Question 1(c) [7 marks]

Define Intrinsic and Extrinsic Semiconductor. Explain P type and N type semiconductors in detail.

Answer:

Semiconductor Type	Description
Intrinsic	Pure semiconductor material with no impurities added
Extrinsic	Semiconductor with controlled impurities added through doping

P-type Semiconductor:

Doping: Created by adding trivalent impurities (boron, gallium, indium) to pure silicon
Hole creation: Each impurity atom creates a hole by accepting valence electrons
Majority carriers: Holes are majority carriers
Minority carriers: Electrons are minority carriers
Electrical properties: Positive charge carriers dominate conduction

N-type Semiconductor:

Doping: Created by adding pentavalent impurities (phosphorus, arsenic, antimony) to pure silicon
Electron creation: Each impurity atom donates an extra electron
Majority carriers: Electrons are majority carriers
Minority carriers: Holes are minority carriers
Electrical properties: Negative charge carriers dominate conduction

Diagram:

+----------------+   +----------------+
| N-type         |   | P-type         |
|                |   |                |
| Si Si Si Si Si |   | Si Si Si Si Si |
|                |   |                |
| Si Si P  Si Si |   | Si Si B  Si Si |
|      |         |   |      |         |
| Si Si|Si Si Si |   | Si Si|Si Si Si |
|      v         |   |      v         |
| Si Si e- Si Si |   | Si Si h+ Si Si |
|                |   |                |
| Si Si Si Si Si |   | Si Si Si Si Si |
+----------------+   +----------------+
  Extra electron       Extra hole

Mnemonic: "PINE" - Positive Impurities make N-type Electrons, Pentavalent donors

Question 1(c) OR [7 marks]

What is filter circuit? Give type and necessity of Filter and Explain "PI" Filter circuit in brief.

Answer:

Filter Circuit: Electronic circuit that removes unwanted frequency components from a signal, allowing desired frequencies to pass through.

Necessity of Filters:

Ripple reduction: Reduces AC ripple from rectifier output
Clean DC: Provides smoother DC output voltage
Component protection: Protects downstream components from voltage fluctuations
Efficiency: Improves overall power supply efficiency

Types of Filters:

Filter Type	Components	Application
Shunt Capacitor	Single capacitor in parallel	Basic filtering
L-Type	Inductor and capacitor	Better filtering
π (Pi) Filter	Two capacitors and one inductor	Superior filtering
RC Filter	Resistor and capacitor	Low-power applications

Pi (π) Filter:

graph LR
    A[Input] --> B[Capacitor C1]
    B --> C[Inductor L]
    C --> D[Capacitor C2]
    D --> E[Output]
    style A fill:#lightblue
    style B fill:#lightgreen
    style C fill:#lightpink
    style D fill:#lightgreen
    style E fill:#lightblue

Working: First capacitor (C1) reduces initial ripple, inductor (L) blocks AC components, second capacitor (C2) filters remaining ripples
Advantage: Provides superior filtering with ripple factor typically below 0.5%
Applications: Used in high-current power supplies where clean DC is critical

Mnemonic: "PIRO" - Pi filters Input Ripples Out effectively

Question 2(a) [3 marks]

Write down different types of capacitors and explain any two.

Answer:

Types of Capacitors:

Ceramic capacitors
Electrolytic capacitors
Tantalum capacitors
Film capacitors
Mica capacitors
Variable capacitors

Ceramic Capacitors:

Construction: Made from ceramic material as dielectric between metal plates
Capacity: 1pF to 1μF
Advantages: Low cost, high stability, non-polarized
Applications: High-frequency filtering, coupling/decoupling

Electrolytic Capacitors:

Construction: Aluminum foil with oxide layer as dielectric
Capacity: 1μF to 10,000μF
Characteristics: Polarized, higher leakage current
Applications: Power supply filtering, audio coupling

Mnemonic: "CAPEX" - Ceramics Are Precise, Electrolytics Expand capacity

Question 2(b) [4 marks]

Explain air core and toroidal inductor.

Answer:

Air Core Inductor:

   +----------+
   |    Air   |
   |          |
 +-|----------|--+
 | |          |  |
 | |          |  |
 | |          |  |
 | |          |  |
 | |          |  |
 +-|----------|--+
   |          |
   +----------+
   Wire windings

Construction: Wire coiled around non-magnetic material (plastic, air)
Properties: Lower inductance, no magnetic core saturation
Applications: High-frequency circuits, RF applications
Advantages: No core losses, linear operation, no saturation

Toroidal Inductor:

      +-------+
     /         \
    /           \
   /     Air     \
  |       +       |
  |      / \      |
  |     /   \     |
  |    +-----+    |
   \   |     |   /
    \  |     |  /
     \ |     | /
      ++-----++
     Wire windings
      around core

Construction: Wire wound around a ring-shaped magnetic core
Properties: Higher inductance, self-shielding magnetic field
Applications: Power supplies, filters, transformers
Advantages: Low electromagnetic interference, efficient flux containment

Mnemonic: "TACO" - Toroids Are Contained, Omnidirectional field reduction

Question 2(c) [7 marks]

Explain Half wave rectifier and Compare different rectifier circuits.

Answer:

Half Wave Rectifier:

graph LR
    A[AC Input] --> B[Transformer]
    B --> C[Diode]
    C --> D[Load]
    C --> E[Ground]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightyellow
    style D fill:#lightgreen
    style E fill:#lightgray

Working Principle:

During positive half-cycle: Diode conducts, current flows through load
During negative half-cycle: Diode blocks, no current flows
Output contains only positive half-cycles of input waveform

Comparison of Rectifiers:

Parameter	Half Wave	Full Wave (Center-Tap)	Bridge Rectifier
Diodes required	1	2	4
Output frequency	f₁ = f_in	f₂ = 2×f_in	f₂ = 2×f_in
Ripple factor	1.21	0.48	0.48
Efficiency	40.6%	81.2%	81.2%
PIV	2V_m	2V_m	V_m
TUF	0.287	0.693	0.812
DC output	V_m/π	2V_m/π	2V_m/π

Mnemonic: "BRIEF" - Bridge Rectifiers Improve Efficiency Fundamentally

Question 2(a) OR [3 marks]

Write down different capacitor specifications and explain any two in detail.

Answer:

Capacitor Specifications:

Capacitance value
Voltage rating
Tolerance
Temperature coefficient
ESR (Equivalent Series Resistance)
Leakage current
Dielectric type

Capacitance Value:

Definition: Amount of electric charge stored per volt
Units: Measured in farads (F), typically microfarads (μF), nanofarads (nF), or picofarads (pF)
Importance: Determines application suitability for coupling, filtering, timing
Marking: Directly printed or color-coded on component

Voltage Rating:

Definition: Maximum voltage that can be applied without breakdown
Specification: Working voltage (WVDC) and surge voltage
Importance: Exceeding rating causes dielectric breakdown and failure
Safety factor: Typically use capacitors rated 50% higher than circuit voltage

Mnemonic: "CAVERN" - Capacitance And Voltage Ensure Reliable Network

Question 2(b) OR [4 marks]

Explain classification of Resistor based on materials.

Answer:

Resistor Type	Material	Properties	Applications
Carbon Composition	Carbon particles + Ceramic binder	High temperature coefficient, noisy	General purpose, surge protection
Carbon Film	Carbon film on ceramic	Better stability than carbon composition	General purpose circuits
Metal Film	Nickel chromium film on ceramic	Low noise, stable, precise	Audio circuits, instrumentation
Wire Wound	Resistance wire around ceramic	High power, low temperature coefficient	Power supplies, high current applications
Metal Oxide	Metal oxide film on ceramic	Stable, high temperature tolerance	High stability applications, power supplies

Characteristics of Carbon Film Resistors:

Temperature coefficient: -250 to 500 ppm/°C
Tolerance: 5% to 10%
Noise: Moderate to low

Characteristics of Metal Film Resistors:

Temperature coefficient: 50 to 100 ppm/°C
Tolerance: 0.1% to 2%
Noise: Very low

Mnemonic: "COMFORT" - Carbon Offers Moderate Films, Others Resist Temperature better

Question 2(c) OR [7 marks]

Explain full wave bridge and center tapped rectifier with diagram and waveform.

Answer:

Full Wave Bridge Rectifier:

graph LR
    A[AC Input] --> B[Transformer]
    B --> C[Bridge<br>Rectifier]
    C --> D[D1]
    C --> E[D2]
    C --> F[D3]
    C --> G[D4]
    D & E & F & G --> H[Load]
    H --> I[Ground]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightyellow
    style H fill:#lightgreen
    style I fill:#lightgray

Working:

Positive half-cycle: D1 and D3 conduct, current flows through load
Negative half-cycle: D2 and D4 conduct, current still flows through load in same direction
Output: Both half-cycles of input converted to positive output

Center Tapped Full Wave Rectifier:

graph LR
    A[AC Input] --> B[Center-Tapped<br>Transformer]
    B -->|Upper Half| C[D1]
    B -->|Lower Half| D[D2]
    C & D --> E[Load]
    E --> F[Ground]
    F --> B
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightyellow
    style D fill:#lightyellow
    style E fill:#lightgreen
    style F fill:#lightgray

Working:

Positive half-cycle: D1 conducts, D2 blocks
Negative half-cycle: D2 conducts, D1 blocks
Output: Both half-cycles of input converted to positive output

Waveforms:

Input:  ∿∿∿∿∿∿∿∿∿∿∿∿∿∿∿
         |
         v
Bridge: ∩∩∩∩∩∩∩∩∩∩∩∩∩∩∩
Rectifier
         |
         v
Output: ∩∩∩∩∩∩∩∩∩∩∩∩∩∩∩
(with filter)

Mnemonic: "FOUR-TWO" - FOUr diodes for Bridge, TWO diodes for Center-Tap

Question 3(a) [3 marks]

Explain the characteristic of Varactor diode.

Answer:

Varactor Diode Characteristics:

graph LR
    A[Reverse Bias<br>Voltage] --> B[Depletion<br>Layer Width]
    B --> C[Junction<br>Capacitance]
    C --> D[Frequency<br>Tuning]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightgreen
    style D fill:#lightyellow

Operating principle: Junction capacitance varies with reverse bias voltage
C-V relationship: Capacitance decreases as reverse voltage increases
Tuning ratio: Typically 4:1 to 10:1 capacitance variation
Applications: Voltage-controlled oscillators, FM modulation, tuning circuits

Mnemonic: "VARA" - Voltage Adjusts Reverse-biased capacitance Automatically

Question 3(b) [3 marks]

State and explain Faraday's laws of electromagnetic induction.

Answer:

Faraday's Laws of Electromagnetic Induction:

First Law:

Statement: Whenever a conductor cuts magnetic flux, an EMF is induced in the conductor
Mathematical expression: EMF ∝ Rate of change of magnetic flux
Application: Basis for generators, transformers, inductors

Second Law:

Statement: The magnitude of induced EMF equals the rate of change of magnetic flux linkage
Mathematical expression: EMF = -N × (dΦ/dt)
- Where: N = number of turns, dΦ/dt = rate of change of flux
Negative sign: Indicates direction (Lenz's Law) - induced current opposes the change

Diagram:

    N     S       
    |     |       
    v     v       
  +---+ +---+     
  |   | |   |     
  |   | |   |     
  +---+ +---+     
    ^     ^       
    |     |       
    |     |       
  +----------+    
  |   Coil   |-----> Induced EMF
  +----------+

Mnemonic: "FACE" - Flux Alteration Creates Electricity

Question 3(c) [7 marks]

Compare different Transistor Configurations.

Answer:

Parameter	Common Emitter (CE)	Common Base (CB)	Common Collector (CC)
Input Terminal	Base	Emitter	Base
Output Terminal	Collector	Collector	Emitter
Common Terminal	Emitter	Base	Collector
Current Gain (α, β, γ)	β = I_C/I_B (20-500)	α = I_C/I_E (0.95-0.99)	γ = I_E/I_B (β+1)
Voltage Gain	High (250-1000)	Medium (150-800)	Less than 1
Input Impedance	Medium (1-2kΩ)	Low (30-150Ω)	High (50-500kΩ)
Output Impedance	High (30-50kΩ)	Very high (250kΩ-1MΩ)	Low (50-100Ω)
Phase Shift	180°	0°	0°
Applications	Amplifiers, oscillators	RF amplifiers, high-frequency circuits	Impedance matching, buffers

Relationship between α, β and γ:

β = α/(1-α)
α = β/(1+β)
γ = β+1

Mnemonic: "BEC" - Base input for Emitter output needs Collector as common terminal

Question 3(a) OR [3 marks]

What is forbidden energy gap? Draw the energy band diagram for insulator, conductor and semiconductor.

Answer:

Forbidden Energy Gap: Energy range in a solid where no electron states exist, separating the valence band from the conduction band.

Energy Band Diagrams:

+---------------+  +---------------+  +---------------+
|///////////////|  |///////////////|  |///////////////|
|/// Conduction |  |/// Conduction |  |/// Conduction |
|///////////////|  |///////////////|  |///////////////|
+---------------+  +---------------+  +---------------+
|               |  |///////////////|  |      |        |
|               |  |///////////////|  |      | Small  |
| Large         |  | Overlap       |  |      | Gap    |
| Forbidden     |  |///////////////|  |      |        |
| Gap (>5eV)    |  |///////////////|  |      | (~1eV) |
|               |  |///////////////|  |      |        |
+---------------+  +---------------+  +---------------+
|///////////////|  |///////////////|  |///////////////|
|/// Valence    |  |/// Valence    |  |/// Valence    |
|///////////////|  |///////////////|  |///////////////|
+---------------+  +---------------+  +---------------+
    Insulator          Conductor        Semiconductor

Insulator: Large forbidden gap (>5eV) prevents electrons from reaching conduction band
Conductor: Overlapping bands allow free electron movement
Semiconductor: Small gap (~1eV) allows some electrons to cross at room temperature or when excited

Mnemonic: "IBCS" - Insulators Block, Conductors Share, Semiconductors have gap Between

Question 3(b) OR [4 marks]

Explain the function of Zener diode as a voltage regulator

Answer:

graph LR
    A[Unregulated<br>DC Input] --> B[Series<br>Resistor]
    B --> C[Load]
    B --> D[Zener<br>Diode]
    D --> E[Ground]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightgreen
    style D fill:#lightyellow
    style E fill:#lightgray

Working Principle:

Normal operation: Zener diode is reverse biased and conducts when voltage reaches breakdown voltage
Voltage regulation: When input voltage rises, more current flows through Zener diode, maintaining constant voltage across it
Load variation: When load draws more current, less current flows through Zener, keeping voltage stable
Series resistor: Limits current and drops excess voltage

Circuit behavior:

V_out = V_z (Zener breakdown voltage)
I_z = (V_in - V_z)/R - I_L

Mnemonic: "SERZ" - Series resistor Enables Regulation with Zener

Question 3(c) OR [7 marks]

Explain V-I char of P-N junction diode and give comparison between P-N junction diode and Zener diode.

Answer:

V-I Characteristics of P-N Junction Diode:

                 I
                 ^
                 |              /
                 |             /
                 |            /
                 |           /
Forward current  |          /
                 |         /
                 |        /
                 |       /
                 |  Knee/
                 |     /
        -V <-----|----+---> +V
                 |   /|
                 |    |
                 |    |
Reverse current  |    |
                 |    |    Breakdown
                 |    |       |
                 |    |       v
                 |    |       ⌄_____

Key Points:

Forward bias: Conducts easily after exceeding knee voltage (~0.7V for silicon)
Reverse bias: Very small leakage current until breakdown voltage
Breakdown region: Occurs at high reverse voltage, causes damage in normal diodes

P-N Junction Diode vs. Zener Diode:

Parameter	P-N Junction Diode	Zener Diode
Symbol	▷\|—	▷\|—◁
Forward operation	Conducts easily	Same as normal diode
Reverse breakdown	At high voltage, causes damage	Controlled, non-destructive
Doping level	Moderate	Heavily doped
Operating region	Forward biased	Reverse biased (breakdown region)
Applications	Rectification, switching	Voltage regulation, reference
Breakdown mechanism	Avalanche	Zener effect and avalanche
Temperature coefficient	Negative	Can be positive or negative

Mnemonic: "FORD" - Forward Operation for Rectifiers, Diodes; reverse operation for Zeners

Question 4(a) [3 marks]

Describe working principle of Photodiode.

Answer:

Working Principle of Photodiode:

graph LR
    A[Light] --> B[P-N Junction]
    B --> C[Electron-Hole<br>Pairs]
    C --> D[Photocurrent]
    style A fill:#lightyellow
    style B fill:#lightpink
    style C fill:#lightblue
    style D fill:#lightgreen

Construction: P-N junction diode with transparent window or lens
Operation: Reverse biased operation for light detection
Photon absorption: Incoming photons create electron-hole pairs in depletion region
Current generation: Electric field sweeps carriers to respective terminals, creating photocurrent
Light sensitivity: Current proportional to light intensity

Mnemonic: "LIGER" - Light Induces Generation of Electrons in Reverse-bias

Question 4(b) [4 marks]

Explain the characteristic of Schottky barrier diode.

Answer:

Schottky Barrier Diode Characteristics:

                 I
                 ^
                 |              /
                 |             / Schottky
                 |            /
                 |           /   PN Junction
Forward current  |          / ,/
                 |         / /
                 |        / /
                 |       / /
                 |      / /
                 |     //
        -V <-----|----|---> +V
                 |    |
                 |    |
                 |    |
Reverse current  |    |
                 |    |

Low forward voltage drop: 0.2-0.3V compared to 0.7V for silicon PN junction
Fast switching: No minority carrier storage, minimal reverse recovery time
Construction: Metal-semiconductor junction instead of P-N junction
No reverse recovery time: Majority carrier device (no stored charge)
Applications: High-frequency applications, rectifiers in power supplies

Mnemonic: "FAST" - Forward voltage low, Allows Switching Timely

Question 4(c) [7 marks]

Explain working principle of PNP and NPN transistor.

Answer:

NPN Transistor Structure and Working:

    +-------+     +-------+     +-------+
    |       |     |       |     |       |
    |   N   |     |   P   |     |   N   |
    |       |     |       |     |       |
    +-------+     +-------+     +-------+
    Emitter        Base        Collector
        |            |            |
        |            |            |
        v            v            v
    Electron      Hole        Electron
     source    controller     collector

Biasing: Emitter-base junction forward biased, collector-base junction reverse biased
Current flow: Electrons from emitter to collector through thin base region
Amplification principle: Small base current controls larger collector current
Current relationship: I_E = I_B + I_C
Majority carriers: Electrons

PNP Transistor Structure and Working:

    +-------+     +-------+     +-------+
    |       |     |       |     |       |
    |   P   |     |   N   |     |   P   |
    |       |     |       |     |       |
    +-------+     +-------+     +-------+
    Emitter        Base        Collector
        |            |            |
        |            |            |
        v            v            v
     Hole         Electron        Hole
     source     controller     collector

Biasing: Emitter-base junction forward biased, collector-base junction reverse biased
Current flow: Holes from emitter to collector through thin base region
Amplification principle: Small base current controls larger collector current
Current relationship: I_E = I_B + I_C
Majority carriers: Holes
Current direction: Opposite to NPN (conventional current from emitter to collector)

Mnemonic: "NPNP" - Negative carriers in NPN, Positive carriers in PNP

Question 4(a) OR [3 marks]

Describe working principle of LED.

Answer:

Working Principle of LED:

graph LR
    A[Forward Bias] --> B[Electron-Hole<br>Recombination]
    B --> C[Energy Release<br>as Photons]
    C --> D[Light Emission]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightyellow
    style D fill:#lightgreen

Construction: P-N junction made from direct bandgap semiconductor materials
Forward biasing: Electrons from n-region and holes from p-region recombine at junction
Recombination: Electrons fall from conduction band to valence band
Energy emission: Energy released during recombination emits photons (light)
Color determination: Bandgap energy determines wavelength (color) of emitted light

Mnemonic: "REBEL" - Recombination of Electrons and holes By Energetic Light emission

Question 4(b) OR [4 marks]

Explain function of transistor as switch in cut off and application of saturation region.

Answer:

Transistor as a Switch:

        Input                        Output
          |                            |
          |                            |
          v                            v
    +----------+                 +----------+
    |    R1    |                 |    RC    |
    +----------+                 +----------+
          |                            |
          |                            |
          |     +---------------+      |
          +---->|     B     C   |------+
                |       |       |
                |       |       |
                |     E         |
                +---------------+
                     |
                     |
                 Ground

Cut-off Region (Switch OFF):

Base voltage: Below 0.7V (for silicon)
Base current: Approximately zero
Collector current: Approximately zero
Collector-emitter voltage: Equal to supply voltage
Applications: Logic gates, digital circuits, relay drivers

Saturation Region (Switch ON):

Base voltage: Well above 0.7V
Base current: Sufficient to ensure minimum V_CE
Collector current: Maximum (limited by collector resistor)
Collector-emitter voltage: Very low (0.2V - 0.3V)
Applications: Digital switches, motor drivers, LED drivers

Mnemonic: "COSI" - Cutoff Opens Switch, Input saturates to close

Question 4(c) OR [7 marks]

Explain common emitter (CE) configuration of Transistor. Derive relation between α and β for transistor amplifier.

Answer:

Common Emitter Configuration:

graph TB
    A[Input Signal] --> B[Base]
    C[Output Signal] --> D[Collector]
    E[Ground] --> F[Emitter]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightgreen
    style D fill:#lightyellow
    style E fill:#lightgray
    style F fill:#lightcyan

Characteristics of Common Emitter Configuration:

Input terminal: Base
Output terminal: Collector
Common terminal: Emitter (grounded)
Current gain (β): High (20-500)
Voltage gain: High (250-1000)
Input impedance: Medium (1-2kΩ)
Output impedance: High (30-50kΩ)
Phase shift: 180° (output inverted from input)

Relationship between α and β:

By definition:

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

From Kirchhoff's Current Law:

I_E = I_B + I_C

Dividing both sides by I_E:

1 = I_B/I_E + I_C/I_E
1 = I_B/I_E + α

Therefore:

I_B/I_E = 1 - α

Now, β = I_C/I_B = (I_C/I_E)/(I_B/I_E) = α/(1-α)

And conversely:

α = β/(1+β)

Mnemonic: "BEAR" - Beta Equals Alpha divided by (1-alpha) Relation

Question 5(a) [3 marks]

What do you mean by E-waste? What are the different methods of E-waste disposal?

Answer:

E-waste (Electronic Waste): Discarded electronic devices and components that have reached end of life or are no longer useful.

Methods of E-waste Disposal:

Disposal Method	Description
Recycling	Separating valuable materials like metals, plastics for reuse
Landfilling	Disposing in designated landfills (not recommended)
Incineration	Burning waste at high temperatures (creates toxic emissions)
Reuse/Refurbishment	Repairing and upgrading for extended use
Extended Producer Responsibility	Manufacturers take back and handle disposal

Mnemonic: "RIPER" - Recycling Is Preferable to Environmentally-harmful Remedies

Question 5(b) [4 marks]

Explain methods of handling electronic waste with examples.

Answer:

Methods of Handling Electronic Waste:

graph LR
    A[E-waste<br>Collection] --> B[Sorting]
    B --> C[Dismantling]
    C --> D[Material<br>Recovery]
    D --> E[Safe<br>Disposal]
    style A fill:#lightblue
    style B fill:#lightpink
    style C fill:#lightyellow
    style D fill:#lightgreen
    style E fill:#lightgray

Collection and Segregation:

Example: Dedicated e-waste bins in public places, e-waste collection drives
Benefit: Prevents mixing with general waste, enables proper processing

Dismantling and Resource Recovery:

Example: Recovering gold, silver, copper from circuit boards and connectors
Benefit: Recovers valuable metals, reduces mining demands

Refurbishment and Reuse:

Example: Repairing old computers for educational institutions
Benefit: Extends product lifecycle, reduces waste generation

Proper Disposal of Hazardous Components:

Example: Specialized treatment for mercury-containing components
Benefit: Prevents toxic substances from entering environment

Mnemonic: "CREED" - Collect, Recover, Extract, Extend, Dispose safely

Question 5(c) [7 marks]

What is ripple factor? Derive the equation of the ripple factor for rectifier.

Answer:

Ripple Factor: Measure of effectiveness of a rectifier's filtering - the ratio of AC component (ripple) to DC component in the output.

Definition:

Ripple factor (γ) = RMS value of AC component / DC value
Lower ripple factor indicates better filtering

Derivation for Half Wave Rectifier:

Let's assume sinusoidal input: v = V_msinωt

For half wave rectifier:

Output is v = V_msinωt for 0 ≤ ωt ≤ π
Output is v = 0 for π ≤ ωt ≤ 2π

Step 1: Find DC component (average value)

V_DC = (1/2π) ∫₀^2π v(ωt) d(ωt)
V_DC = (1/2π) ∫₀^π V_msinωt d(ωt)
V_DC = V_m/π

Step 2: Find RMS value

V_RMS = √[(1/2π) ∫₀^2π v²(ωt) d(ωt)]
V_RMS = √[(1/2π) ∫₀^π V_m²sin²ωt d(ωt)]
V_RMS = V_m/2

Step 3: Find AC component

V_AC² = V_RMS² - V_DC²
V_AC² = (V_m/2)² - (V_m/π)²
V_AC² = V_m²(1/4 - 1/π²)

Step 4: Calculate ripple factor

γ = V_AC/V_DC
γ = √(V_m²(1/4 - 1/π²))/(V_m/π)
γ = π√(1/4 - 1/π²)
γ = 1.21 (for half wave rectifier)

For Full Wave Rectifier: Following similar steps leads to γ = 0.48

Mnemonic: "ROAD" - Ripple is Output's AC Divided by DC component

Question 5(a) OR [3 marks]

Which are the toxic substances present in e-waste?

Answer:

Toxic Substances in E-waste:

Toxic Substance	Source in Electronics	Health/Environmental Impact
Lead (Pb)	Solder, CRT monitors, batteries	Neurological damage, developmental issues
Mercury (Hg)	Switches, backlights, batteries	Neurological and kidney damage
Cadmium (Cd)	Rechargeable batteries, circuit boards	Kidney damage, bone disease
Brominated Flame Retardants	Plastic casings, circuit boards	Endocrine disruption, bioaccumulation
Hexavalent Chromium	Corrosion protection in metal parts	Allergic reactions, DNA damage
Beryllium (Be)	Connectors, springs	Lung disease, skin disorders

Mnemonic: "LMBCHB" - Lead, Mercury, and Beryllium Cause Harmful Bodily effects

Question 5(b) OR [4 marks]

Write important parameters for selecting the right transistor for your application and explain any two.

Answer:

Important Transistor Selection Parameters:

Maximum collector current (I_C)
Maximum collector-emitter voltage (V_CEO)
Maximum collector-base voltage (V_CBO)
Current gain (hFE or β)
Frequency response (f_T)
Power dissipation (P_tot)
Package type (TO-3, SMT, etc.)
Temperature range

Maximum Collector Current (I_C):

Definition: Maximum current that can flow through collector without damage
Importance: Must exceed application's peak current requirements with safety margin
Typical values: 100mA to 100A depending on transistor type
Application consideration: Select 50% higher rating than maximum required current

Current Gain (hFE or β):

Definition: Ratio of collector current to base current
Importance: Determines amplification capability and required base drive
Typical values: 20-500 for general-purpose transistors
Application consideration: For switching, high gain reduces base current requirement; for amplifiers, consistent gain across operating range is important

Mnemonic: "GIVE" - Gain and Ic are Very Essential parameters

Question 5(c) OR [7 marks]

What is rectifier efficiency? Find out efficiency of the full wave rectifier.

Answer:

Rectifier Efficiency: The ratio of DC output power to the AC input power, expressed as a percentage.

Definition:

Efficiency (η) = (P_DC/P_AC) × 100%
Higher efficiency means better conversion of AC to DC power

Derivation for Full Wave Rectifier:

Step 1: Calculate DC output power

I_DC = V_DC/R_L
P_DC = I_DC² × R_L = V_DC²/R_L
For full wave, V_DC = 2V_m/π
P_DC = (2V_m/π)²/R_L = 4V_m²/(π²R_L)

Step 2: Calculate AC input power

I_RMS = V_RMS/R_L
P_AC = I_RMS² × R_L = V_RMS²/R_L
For sine wave, V_RMS = V_m/√2
P_AC = (V_m/√2)²/R_L = V_m²/(2R_L)

Step 3: Calculate efficiency

η = (P_DC/P_AC) × 100%
η = [4V_m²/(π²R_L)] / [V_m²/(2R_L)] × 100%
η = [4/(π²)] × 2 × 100%
η = 8/(π²) × 100%
η = 8/9.87 × 100%
η = 81.2%

Full Wave Rectifier Efficiency = 81.2%

For comparison:

Half Wave Rectifier Efficiency = 40.6%
Bridge Rectifier Efficiency = 81.2%

Mnemonic: "PIDE" - Power Input Determines Efficiency