Question 1 [14 marks]

Answer any seven out of ten.

Question 1(1) [2 marks]

Define resistor and give its unit.

Answer: A resistor is an electronic component that opposes the flow of electric current. Its unit is Ohm (Ω).

Table: Resistor Properties

Property	Description
Symbol	⏅
Unit	Ohm (Ω)
Function	Limits current flow

Mnemonic: "Resistors Oppose Current" (ROC)

Question 1(2) [2 marks]

Give two examples of active and passive components each.

Answer:

Table: Electronic Components Classification

Active Components	Passive Components
1. Transistors	1. Resistors
2. Diodes	2. Capacitors

Mnemonic: "TARD" - Transistors And Resistors Differ

Question 1(3) [2 marks]

Draw symbols of any two semiconductor devices.

Answer:

Diagram:

graph TD
    subgraph Diode
        A[Plus] --> B["|<|"] --> C[Minus]
    end

    subgraph NPN_Transistor
        D[C] --> E
        F[E] --> E
        G[B] --> E
    end

Mnemonic: "Diodes Direct, Transistors Transfer"

Question 1(4) [2 marks]

Differentiate between intrinsic and extrinsic semiconductor.

Answer:

Table: Intrinsic vs Extrinsic Semiconductors

Intrinsic	Extrinsic
Pure semiconductor without impurities	Semiconductor with added impurities
Equal number of holes and electrons	Unequal holes and electrons
Examples: Pure Silicon, Germanium	Examples: Silicon doped with Phosphorus

Mnemonic: "Pure In, Doped Ex"

Question 1(5) [2 marks]

LED stands for _________________.

Answer: LED stands for Light Emitting Diode.

Diagram:

graph LR
    A[Light] --> B[Emitting] --> C[Diode]
    style A fill:#f96,stroke:#333
    style B fill:#9cf,stroke:#333
    style C fill:#f9f,stroke:#333

Mnemonic: "Light Emitters Dazzle"

Question 1(6) [2 marks]

State any two applications of Photo-diode.

Answer:

Table: Photo-diode Applications

Application	How it works
Light sensors	Converts light to electrical current
Optical communication	Detects optical signals in fiber optics

Mnemonic: "Light Sensing Communication" (LSC)

Question 1(7) [2 marks]

List the types of transistor and draw their symbols.

Answer:

Types of Transistors:

NPN Transistor
PNP Transistor

Diagram:

graph TD
    subgraph "NPN"
    A[C] --- B --- C[E]
    D[B] --- B
    end
    subgraph "PNP"
    E[E] --- F --- G[C]
    H[B] --- F
    end

Mnemonic: "Not Pointing iN, Pointing outP"

Question 1(8) [2 marks]

Give the value of forward voltage drop of Germanium and Silicon diode.

Answer:

Table: Forward Voltage Drop Values

Diode Type	Forward Voltage Drop
Germanium	0.3V
Silicon	0.7V

Mnemonic: "Germanium's Three, Silicon's Seven" (0.3V, 0.7V)

Question 1(9) [2 marks]

The _________________ diode can be used as a light detector.

Answer: The Photodiode can be used as a light detector.

Diagram:

graph LR
    A[Light] -->|detected by| B[Photodiode]
    B -->|generates| C[Current]
    style A fill:#ff9,stroke:#333
    style B fill:#9cf,stroke:#333
    style C fill:#f96,stroke:#333

Mnemonic: "Photo Detects Light" (PDL)

Question 1(10) [2 marks]

Define Q-factor of a coil.

Answer: Q-factor (Quality factor) of a coil is the ratio of its inductive reactance to its resistance, indicating how efficiently it stores energy.

Table: Q-Factor

Parameter	Description
Formula	Q = XL/R
Higher Q	Better quality, less energy loss
Lower Q	Poor quality, more energy loss

Mnemonic: "Quality equals Reactance over Resistance" (QRR)

Question 2(a) [3 marks]

Explain colour coding method of resistor.

Answer:

Resistor color coding uses colored bands to indicate resistance value and tolerance.

Table: Resistor Color Code

Color	Digit	Multiplier
Black	0	10⁰
Brown	1	10¹
Red	2	10²
Orange	3	10³
Yellow	4	10⁴

For a 4-band resistor:

First band: First digit
Second band: Second digit
Third band: Multiplier
Fourth band: Tolerance

Mnemonic: "Bad Boys Race Our Young Girls But Violet Generally Wins" (Colors in order: Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey, White)

Question 2(a) OR [3 marks]

Explain Light Dependent Resistor with its characteristics.

Answer:

LDR is a resistor whose resistance decreases when light intensity increases.

Characteristics of LDR:

Table: LDR Properties

Parameter	Behavior
Dark condition	High resistance (MΩ)
Bright condition	Low resistance (kΩ)
Response time	Few milliseconds

Diagram:

graph TD
    A[Increase Light] -->|Causes| B[Decrease Resistance]
    C[Decrease Light] -->|Causes| D[Increase Resistance]
    style A fill:#ff9,stroke:#333
    style B fill:#9cf,stroke:#333
    style C fill:#999,stroke:#333
    style D fill:#f96,stroke:#333

Mnemonic: "Light Up, Resistance Down" (LURD)

Question 2(b) [3 marks]

Explain classification of capacitors in detail.

Answer:

Capacitors are classified based on dielectric material and construction.

Table: Capacitor Classifications

Type	Dielectric	Applications
Ceramic	Ceramic	High frequency
Electrolytic	Aluminum oxide	Power supplies
Polyester	Plastic film	General purpose
Tantalum	Tantalum oxide	Small, high capacity

Diagram:

graph TD
    A[Capacitors] --> B[Fixed]
    A --> C[Variable]
    B --> D[Ceramic]
    B --> E[Electrolytic]
    B --> F[Polyester/Film]
    C --> G[Air Gang]
    C --> H[Trimmer]
    style A fill:#f96,stroke:#333

Mnemonic: "CEPT" (Ceramic, Electrolytic, Polyester, Tantalum)

Question 2(b) OR [3 marks]

Explain classification of inductor in detail.

Answer:

Inductors are classified based on core material and construction.

Table: Inductor Classifications

Type	Core	Characteristics
Air core	Air	Low inductance, low losses
Iron core	Iron	High inductance, high losses
Ferrite core	Ferrite	Medium inductance, low losses
Toroidal	Ring shaped	High efficiency, low EMI

Diagram:

graph TD
    A[Inductors] --> B[Air Core]
    A --> C[Iron Core]
    A --> D[Ferrite Core]
    A --> E[Toroidal]
    style A fill:#9cf,stroke:#333

Mnemonic: "Air Iron Ferrite Toroid" (AIFT)

Question 2(c) [4 marks]

State and explain Faraday's laws of Electromagnetic Induction.

Answer:

Faraday's laws explain how electromagnetic induction works.

Faraday's First Law: When a magnetic field linked with a conductor changes, an EMF is induced in the conductor.

Faraday's Second Law: The magnitude of induced EMF is proportional to the rate of change of magnetic flux.

Table: Faraday's Laws Summary

Law	Statement	Formula
First Law	Change in magnetic field induces EMF	-
Second Law	EMF ∝ rate of change of flux	E = -N(dΦ/dt)

Diagram:

graph LR
    A[Moving Magnet] -->|Creates| B[Changing Magnetic Field]
    B -->|Induces| C[EMF in Conductor]
    style A fill:#f96,stroke:#333
    style B fill:#9cf,stroke:#333
    style C fill:#ff9,stroke:#333

Mnemonic: "Change Magnetic Field, Create Electric Current" (CMFCEC)

Question 2(c) OR [4 marks]

Enlist specifications of capacitors and explain two in detail.

Answer:

Specifications of Capacitors:

Capacitance value
Voltage rating
Tolerance
Leakage current
Temperature coefficient

Detailed Explanation:

Capacitance Value: The amount of charge a capacitor can store per volt, measured in Farads (F).

Voltage Rating: The maximum voltage that can be applied without damaging the capacitor.

Table: Capacitor Specifications

Specification	Description	Typical Values
Capacitance	Charge storage capacity	pF to mF
Voltage Rating	Maximum safe voltage	16V, 25V, 50V, etc.

Diagram:

graph TD
    A[Capacitor Specifications] --> B[Capacitance Value]
    A --> C[Voltage Rating]
    A --> D[Tolerance]
    A --> E[Leakage Current]
    A --> F[Temperature Coefficient]
    style A fill:#9cf,stroke:#333

Mnemonic: "Capacitors Very Tolerant of Low Temperatures" (CVTLT)

Question 2(d) [4 marks]

Write colour band of 47Ω±5% resistance.

Answer:

For 47Ω±5% resistor, the color bands are:

Table: Color Bands for 47Ω±5%

Band	Color	Represents
1st band	Yellow	4
2nd band	Violet	7
3rd band	Black	×10⁰
4th band	Gold	±5%

Diagram:

graph LR
    A[Yellow] -->|4| B[Violet] -->|7| C[Black] -->|×10⁰| D[Gold] -->|±5%| E[47Ω±5%]
    style A fill:#ff9,stroke:#333
    style B fill:#f0f,stroke:#333
    style C fill:#000,stroke:#fff
    style D fill:#fd0,stroke:#333
    style E fill:#fff,stroke:#333

Mnemonic: "Yellow Violets Bring Gold" (The colors of the bands)

Question 2(d) OR [4 marks]

Calculate value of resistor and tolerance for a given colour code: Brown, Black, yellow.

Answer:

Table: Interpretation of Brown, Black, Yellow

Band	Color	Value	Meaning
1st	Brown	1	First digit
2nd	Black	0	Second digit
3rd	Yellow	10⁴	Multiplier

Calculation: 1st digit: 1 2nd digit: 0 Multiplier: 10⁴

Value = 10 × 10⁴ = 100,000Ω = 100kΩ

No 4th band means ±20% tolerance

Diagram:

graph LR
    A[Brown] -->|1| B[Black] -->|0| C[Yellow] -->|×10⁴| D[100kΩ ±20%]
    style A fill:#a52a2a,stroke:#333
    style B fill:#000,stroke:#fff
    style C fill:#ff0,stroke:#333
    style D fill:#fff,stroke:#333

Mnemonic: "Big Black Yield" (Brown-Black-Yellow)

Question 3(a) [3 marks]

Define doping. Give the name of semiconductor materials fabricated by doping with an example of each.

Answer:

Doping is the process of adding impurities to a pure semiconductor to modify its electrical properties.

Table: Doped Semiconductors

Type	Dopant Added	Example	Majority Carriers
P-type	Trivalent (Boron, Gallium)	Silicon doped with Boron	Holes
N-type	Pentavalent (Phosphorus, Arsenic)	Silicon doped with Phosphorus	Electrons

Diagram:

graph LR
    A[Pure Semiconductor] --> B[Add Trivalent Impurity] --> C[P-type]
    A --> D[Add Pentavalent Impurity] --> E[N-type]
    style A fill:#9cf,stroke:#333
    style C fill:#f96,stroke:#333
    style E fill:#99f,stroke:#333

Mnemonic: "Positive has Plus Holes, Negative has Numerous Electrons" (PHNE)

Question 3(a) OR [3 marks]

Define Ripple factor, Peak Inverse Voltage (PIV), Rectification efficiency.

Answer:

Table: Rectifier Terms

Term	Definition	Formula
Ripple Factor	Measure of AC component in rectified output	r = Vrms(AC)/Vdc
Peak Inverse Voltage	Maximum reverse voltage a diode can withstand	-
Rectification Efficiency	Ratio of DC output power to AC input power	η = (Pdc/Pac) × 100%

Diagram:

graph TD
    A[Rectifier Parameters] --> B[Ripple Factor]
    A --> C[Peak Inverse Voltage]
    A --> D[Rectification Efficiency]
    style A fill:#9cf,stroke:#333

Mnemonic: "Ripples Peak Efficiently" (RPE)

Question 3(b) [3 marks]

Explain working of Crystal diode.

Answer:

Crystal diode is a point-contact diode made with a semiconductor crystal.

Table: Crystal Diode Properties

Property	Description
Construction	Metal point contact on semiconductor crystal
Function	Rectification of high frequency signals
Application	Radio signal detection

Diagram:

graph LR
    A[RF Signal] --> B[Crystal Diode] --> C[Rectified Signal]
    style A fill:#9cf,stroke:#333
    style B fill:#f96,stroke:#333
    style C fill:#9f9,stroke:#333

Mnemonic: "Crystal Detects Radio Frequencies" (CDRF)

Question 3(b) OR [3 marks]

Explain working of photodiode.

Answer:

Photodiode converts light energy into electrical current when operated in reverse bias.

Table: Photodiode Characteristics

Parameter	Behavior
Light condition	Generates electron-hole pairs
Reverse current	Increases with light intensity
Speed	Fast response time

Diagram:

graph LR
    A[Light] -->|Strikes| B[PN Junction]
    B -->|Creates| C[Electron-Hole Pairs]
    C -->|Produces| D[Current Flow]
    style A fill:#ff9,stroke:#333
    style D fill:#9cf,stroke:#333

Mnemonic: "Light In, Current Out" (LICO)

Question 3(c) [4 marks]

Explain half-wave rectifier with circuit diagram and waveforms.

Answer:

Half-wave rectifier converts AC to pulsating DC by allowing current flow only during positive half cycles.

Circuit Diagram:

graph LR
    A[AC Input] --- B[Transformer] --- C[Diode] --- D[Load Resistor] --- E[Ground]
    E --- A
    style A fill:#9cf,stroke:#333
    style D fill:#f96,stroke:#333

Waveforms:

graph TD
    subgraph "Input AC"
    A[+Vp] --- B[(0)] --- C[-Vp]
    end
    subgraph "Output DC"
    D[+Vp] --- E[(0)] --- F[(0)]
    end
    style A fill:#9cf,stroke:#333
    style C fill:#9cf,stroke:#333
    style D fill:#f96,stroke:#333

Table: Half-Wave Rectifier Properties

Parameter	Value
Ripple Factor	1.21
Efficiency	40.6%
Output Frequency	Same as input

Mnemonic: "Half Wave Passes Half" (HWPH)

Question 3(c) OR [4 marks]

Explain full-wave rectifier with circuit diagram and waveforms.

Answer:

Full-wave rectifier converts both halves of AC input to pulsating DC output.

Circuit Diagram (Bridge type):

graph LR
    A[AC Input] --- B[D1]
    A --- C[D3]
    B --- D[D2] --- E[+Output]
    C --- F[D4] --- G[-Output]
    E --- H[Load] --- G
    style A fill:#9cf,stroke:#333
    style H fill:#f96,stroke:#333

Waveforms:

graph TD
    subgraph "Input AC"
    A[+Vp] --- B[(0)] --- C[-Vp] --- B
    end
    subgraph "Output DC"
    D[+Vp] --- E[(0)] --- D
    end
    style A fill:#9cf,stroke:#333
    style C fill:#9cf,stroke:#333
    style D fill:#f96,stroke:#333

Table: Full-Wave Rectifier Properties

Parameter	Value
Ripple Factor	0.48
Efficiency	81.2%
Output Frequency	Twice the input

Mnemonic: "Full Wave Makes Full Use" (FWMFU)

Question 3(d) [4 marks]

Draw and explain VI characteristics of PN junction diode.

Answer:

VI Characteristics:

graph TD
    subgraph "Forward Bias"
    A[Vf] --> B[If]
    end
    subgraph "Reverse Bias"
    C[Vr] --> D[Ir]
    E[Breakdown] --> F[Reverse Current Increases]
    end
    style A fill:#9cf,stroke:#333
    style C fill:#f96,stroke:#333
    style E fill:#f00,stroke:#333

Table: PN Junction Diode Characteristics

Region	Behavior
Forward Bias	Current increases exponentially after 0.7V (Si)
Reverse Bias	Very small leakage current flows
Breakdown	Occurs at high reverse voltage, current increases rapidly

Forward Bias: Positive voltage to P-side, current flows easily after threshold. Reverse Bias: Positive voltage to N-side, only small leakage current flows.

Mnemonic: "Forward Flows, Reverse Restricts" (FFRR)

Question 3(d) OR [4 marks]

Write difference between P-type and N-type semiconductor.

Answer:

Table: P-type vs N-type Semiconductor

Property	P-type	N-type
Dopant	Trivalent (Boron, Gallium)	Pentavalent (Phosphorus, Arsenic)
Majority Carriers	Holes	Electrons
Minority Carriers	Electrons	Holes
Electrical Charge	Relatively Positive	Relatively Negative
Conductivity	Lower than N-type	Higher than P-type

Diagram:

graph LR
    subgraph "P-type"
    A[Silicon] --- B[Boron]
    C[Holes] --- D[+]
    end
    subgraph "N-type"
    E[Silicon] --- F[Phosphorus]
    G[Electrons] --- H[-]
    end
    style C fill:#f96,stroke:#333
    style G fill:#9cf,stroke:#333

Mnemonic: "Positive has Plus Holes, Negative has Numerous Electrons" (PHNE)

Question 4(a) [3 marks]

Explain the principle of operation of LED.

Answer:

LED (Light Emitting Diode) emits light when forward biased due to electron-hole recombination.

Principle of Operation: When forward biased, electrons from N-side move to P-side and recombine with holes, releasing energy as photons (light).

Table: LED Operation

Process	Result
Forward bias	Current flows
Electron-hole recombination	Energy release
Energy band gap	Determines color

Diagram:

graph LR
    A[Forward Bias] -->|Causes| B[Current Flow]
    B -->|Creates| C[Electron-Hole Recombination]
    C -->|Releases| D[Photons or Light]

Mnemonic: "Forward Current Emits Light" (FCEL)

Question 4(a) OR [3 marks]

State applications of LED.

Answer:

Table: LED Applications

Application	Advantage
Display indicators	Low power consumption
Digital displays	Varied colors available
Lighting	Energy efficient
Remote controls	Infrared communication
Traffic signals	Long life, high visibility

Diagram:

graph TD
    A[LED Applications] --> B[Indicators]
    A --> C[Displays]
    A --> D[Lighting]
    A --> E[Communication]
    A --> F[Signals]
    style A fill:#9cf,stroke:#333

Mnemonic: "Display Lights In Clever Signals" (DLICS)

Question 4(b) [4 marks]

Explain Zener diode as voltage regulator.

Answer:

Zener diode maintains constant output voltage despite input voltage fluctuations when operated in reverse breakdown region.

Circuit:

graph LR
    A[Unregulated DC] --- B[Series Resistor] --- C[Output]
    C --- D[Zener Diode] --- E[Ground]
    C --- F[Load] --- E
    style A fill:#9cf,stroke:#333
    style C fill:#9f9,stroke:#333
    style D fill:#f96,stroke:#333

Working:

Series resistor limits current
Zener operates in breakdown region
Maintains constant voltage across load

Table: Zener Regulator Characteristics

Parameter	Description
Voltage regulation	Maintains constant output despite input changes
Power rating	Must handle power dissipation
Temperature stability	Output varies slightly with temperature

Mnemonic: "Zeners Break to Regulate" (ZBR)

Question 4(b) OR [4 marks]

Give limitations of zener voltage regulator.

Answer:

Table: Limitations of Zener Voltage Regulator

Limitation	Effect
Power Dissipation	Limited by zener power rating
Current Capacity	Can handle only small loads
Temperature Sensitivity	Output varies with temperature
Efficiency	Poor efficiency due to power loss in series resistor
Noise	Generates electrical noise

Diagram:

graph TD
    A[Zener Limitations] --> B[Power Limits]
    A --> C[Current Limits]
    A --> D[Temperature Effects]
    A --> E[Efficiency Issues]
    A --> F[Noise Generation]
    style A fill:#f96,stroke:#333

Mnemonic: "Power Current Temperature Efficiency Noise" (PCTEN)

Question 4(c) [7 marks]

Discuss the necessity of filter circuit in rectifier. List various types of filter circuits used in rectifier and explain any one with neat diagram.

Answer:

Necessity of Filter Circuit: Rectifier output contains AC ripple that must be removed for smoother DC. Filters reduce these ripples to provide steady DC output.

Types of Filter Circuits:

Capacitor filter (Shunt capacitor)
LC filter
π-filter (Pi-filter)
RC filter

Explanation of Capacitor Filter:

Circuit Diagram:

graph LR
    A[Rectifier Output] --- B[+]
    B --- C[Load]
    B --- D[Capacitor]
    C --- E[Ground]
    D --- E
    style A fill:#9cf,stroke:#333
    style C fill:#f96,stroke:#333
    style D fill:#9f9,stroke:#333

Working:

Capacitor charges during voltage peaks
Discharges slowly during voltage drops
Maintains output voltage between peaks
Reduces ripple voltage

Table: Capacitor Filter Characteristics

Parameter	Effect
Capacitance value	Higher value gives less ripple
Ripple reduction	Typically reduces by 70-80%
Load current	Higher load current causes more ripple
Frequency	Higher frequency is easier to filter

Waveforms:

graph TD
    subgraph "Rectifier Output"
    A[Pulsating DC]
    end
    subgraph "Filter Output"
    B[Smoother DC]
    end
    style A fill:#f96,stroke:#333
    style B fill:#9f9,stroke:#333

Mnemonic: "Capacitors Hold Voltage During Drops" (CHVDD)

Question 5(a) [3 marks]

Define e-waste. List common e-waste items.

Answer:

E-waste refers to discarded electronic devices and components that have reached the end of their useful life.

Table: Common E-waste Items

Category	Examples
Computing devices	Computers, laptops, tablets
Communication devices	Mobile phones, telephones
Home appliances	TVs, refrigerators, washing machines
Electronic components	Circuit boards, batteries, cables
Office equipment	Printers, scanners, copiers

Diagram:

graph TD
    A[E-waste] --> B[Computing]
    A --> C[Communication]
    A --> D[Home Appliances]
    A --> E[Components]
    A --> F[Office Equipment]
    style A fill:#f96,stroke:#333

Mnemonic: "Computers, Communication, Components, Home Appliances" (CCCHA)

Question 5(b) [3 marks]

State and explain various strategies of e-waste management.

Answer:

Table: E-waste Management Strategies

Strategy	Description
Reduce	Minimize purchase of new electronics
Reuse	Extend life through repair and repurposing
Recycle	Process e-waste to recover valuable materials
Responsible disposal	Use authorized e-waste collection centers
Extended producer responsibility	Manufacturers take back end-of-life products

Diagram:

graph TD
    A[E-waste Management] --> B[Reduce]
    A --> C[Reuse]
    A --> D[Recycle]
    A --> E[Responsible Disposal]
    A --> F[Extended Producer Responsibility]
    style A fill:#9cf,stroke:#333

Mnemonic: "3R's

Question 5(c) [4 marks]

Explain transistor as switch.

Answer:

Transistor can function as an electronic switch by operating in either cutoff (OFF) or saturation (ON) region.

Table: Transistor Switch Operation

State	Condition	Behavior
OFF (Cutoff)	Base current = 0	No collector current flows
ON (Saturation)	Base current sufficient	Maximum collector current flows

Circuit Diagram:

graph LR
    A[+Vcc] --- B[Rc] --- C[Collector]
    C --- D[Emitter] --- E[Ground]
    F[Vin] --- G[Rb] --- H[Base]
    H --- D
    style F fill:#9cf,stroke:#333
    style A fill:#f96,stroke:#333

Working:

When input is HIGH: Transistor saturates, acts like closed switch
When input is LOW: Transistor cuts off, acts like open switch

Mnemonic: "No Base No Current, Apply Base Connect Circuit" (NBNC-ABC)

Question 5(d) [4 marks]

Derive relation between α and β for CE configuration of transistor.

Answer:

In transistors, α (alpha) and β (beta) are current gain parameters.

Definitions:

α = IC/IE (Common Base current gain)
β = IC/IB (Common Emitter current gain)

Derivation: Since IE = IC + IB, we can write: α = IC/IE = IC/(IC + IB)

Dividing numerator and denominator by IB: α = (IC/IB)/[(IC/IB) + 1] = β/(β + 1)

Therefore: β = α/(1-α)

Table: Relationship between α and β

Parameter	Formula	Typical Range
α from β	α = β/(β+1)	0.9 to 0.99
β from α	β = α/(1-α)	50 to 300

Diagram:

graph TD
    A[alpha = IC divided by IE] --- B[beta = IC divided by IB]
    C[beta = alpha divided by 1 minus alpha] --- D[alpha = beta divided by beta plus 1]

    style A fill:#9cf,stroke:#333
    style B fill:#f96,stroke:#333

Mnemonic: "Beta equals Alpha divided by One minus Alpha" (BAOA)