Concept of Basic Electrical and Electronics Engineering

1

Think of electricity like water: voltage (V) is the pressure, current (I) is the flow rate, and resistance (R) is how narrow the pipe is. Ohm's Law: V = IR.

2

Three forms of power — all equivalent, use whichever two quantities you know: P = VI, P = I²R, P = V²/R. Pick the form that uses the two values you already have.

3

Energy E = P × t. Your electricity bill measures kilowatt-hours (kWh) — a 2 kW heater running 3 hours consumes 6 kWh.

4

Conductors (copper, aluminium, silver) have loosely held outer electrons that drift easily under voltage. Insulators (rubber, glass, PVC) hold electrons tightly — no free carriers.

5

Series circuit: only ONE path exists, so the same current flows through every element. Voltage splits across resistors proportionally (voltage divider).

6

Parallel circuit: every branch shares the same terminal voltage. Current divides — larger resistance gets less current. Rule: 1/R_total = 1/R₁ + 1/R₂ + …

7

A vital insight: adding resistors in parallel ALWAYS lowers total resistance (more paths = less opposition). Adding in series always raises it.

8

KCL (Kirchhoff's Current Law): at any junction, all currents flowing in equal all currents flowing out. Charge cannot pile up — conservation of charge.

9

KVL (Kirchhoff's Voltage Law): going around any closed loop and summing all voltage rises and drops gives exactly zero — conservation of energy.

10

Linear element: doubling voltage doubles current (V ∝ I). Non-linear element: V and I are NOT proportional — a diode is the classic example (exponential curve).

11

Bilateral element: behaves identically regardless of current direction (resistor, capacitor). Unilateral element: only conducts one way (diode, transistor).

12

Active element: a source that *delivers* energy to the circuit (battery, generator). Passive element: *absorbs or stores* energy only (resistor, capacitor, inductor).

13

Star-Delta (Y-Δ) conversion: transforms a 3-terminal star resistor network into an equivalent delta — useful when plain series/parallel simplification fails.

1

Superposition theorem: in any LINEAR network with multiple sources, the total response equals the sum of each source's individual contribution (deactivate others: short voltage sources, open current sources).

2

Thevenin's theorem condenses any complex two-terminal linear network into just ONE voltage source (Vth) plus ONE series resistance (Rth). Enormously simplifies load calculations.

3

Norton's theorem is Thevenin's current-source equivalent: one current source (In) in parallel with Rn. Convert between them: Vth = In × Rn, and ==Rth = Rn==.

4

Maximum power transfer theorem: maximum power is delivered to a load when R_load = R_source (= Rth). At this point efficiency is exactly 50%.

5

Inductive reactance X_L = 2πfL (Ω). It INCREASES with frequency — an inductor resists changes in current (opposes AC more at higher frequencies).

6

Capacitive reactance X_C = 1/(2πfC) (Ω). It DECREASES with frequency — a capacitor blocks DC completely (X_C → ∞ at f = 0).

7

Series RLC impedance: Z = √(R² + (X_L − X_C)²). Phase angle φ = arctan((X_L − X_C)/R).

8

ELI the ICE man: in an Inductor (L), EMF leads I — so current LAGS by 90°. In a Capacitor (C), I leads E — current LEADS by 90°.

9

Resonance occurs when X_L = X_C (they cancel). Resonant frequency: f₀ = 1 / (2π√(LC)).

10

At series resonance: impedance is MINIMUM (= R only), so current is MAXIMUM.

11

At parallel resonance: impedance is MAXIMUM, so line current is MINIMUM.

12

Power triangle: Real power P = VIcosφ (Watts, actual work done). Reactive power Q = VIsinφ (VAR, stored/returned). Apparent power S = VI (VA). Relation: S² = P² + Q².

13

Power factor = cosφ = P/S. Unity PF (PF = 1) is ideal. Inductive loads → lagging PF. Capacitive loads → leading PF.

1

AC is generated by electromagnetic induction: a coil rotating in a magnetic field produces a sinusoidally varying EMF — this is Faraday's law in action.

2

Instantaneous voltage: v = Vm · sin(ωt), where Vm is the peak (maximum) value, ω = 2πf is the angular frequency in rad/s.

3

Frequency f = number of complete cycles per second (Hz). Period T = 1/f seconds. Nepal's power grid runs at 50 Hz (T = 20 ms).

4

RMS (Root Mean Square) value: V_rms = Vm/√2 ≈ 0.707 Vm. This is the most practically useful value — it's what your voltmeter reads.

5

The RMS value is the DC-equivalent: a 230 V RMS AC supply produces the same heating in a resistor as a 230 V DC supply.

6

Average value (over a positive half-cycle): V_avg = 2Vm/π ≈ 0.637 Vm.

7

Form factor = RMS / Average = 1.11 for a pure sine wave. It tells you how 'peaky' a waveform is.

8

Peak (crest) factor = Peak / RMS = √2 ≈ 1.414 for a sine wave.

9

Three-phase AC has three voltage waveforms, each 120° apart in phase. It is more efficient than single-phase for power transmission.

10

Star (Y) connection: V_line = √3 × V_phase; I_line = I_phase.

11

Delta (Δ) connection: V_line = V_phase; I_line = √3 × I_phase.

1

Semiconductors (silicon, germanium) sit between conductors and insulators — their conductivity can be controlled by doping (adding impurities).

2

N-type doping adds donor atoms (phosphorus, arsenic) — extra electrons become the majority carriers.

3

P-type doping adds acceptor atoms (boron, indium) — holes become the majority carriers.

4

A PN junction diode conducts (low resistance) in forward bias and blocks (very high resistance) in reverse bias — it's a one-way valve for current.

5

Forward voltage drop: ~0.7 V for silicon, ~0.3 V for germanium. Below this threshold, the diode is effectively off.

6

Main use of a diode: rectification — converting AC to DC (half-wave or full-wave rectifier circuits).

7

Zener diode is engineered for controlled reverse breakdown at a precise voltage (Zener voltage). This makes it ideal for voltage regulation.

8

BJT (Bipolar Junction Transistor) has three terminals: Emitter (E), Base (B), Collector (C). Two types: NPN and PNP.

9

BJT is a CURRENT-controlled device: a small base current controls a much larger collector current. Current gain β (hFE) = I_C / I_B.

10

Three BJT configurations: Common Emitter (CE) — highest power gain, used most; Common Base (CB) — high frequency; Common Collector (CC) — unity gain, high current.

11

BJT operates in: Active region (amplifier), Saturation (switch ON), Cutoff (switch OFF).

12

MOSFET is a VOLTAGE-controlled transistor. Gate-source voltage (V_GS) controls the drain current. Very high input impedance (gate draws almost no current).

13

CMOS = Complementary MOS (NMOS + PMOS pair). Consumes power only during switching — that's why it dominates digital ICs with extremely low static power.

1

An oscillator is a circuit that generates a continuous periodic waveform (sine, square, etc.) with NO external input signal. It sustains itself by converting DC power to AC.

2

Every oscillator relies on POSITIVE feedback: a portion of the output is fed back in phase with the input to continuously reinforce the oscillation.

3

Barkhausen criterion (necessary condition for sustained oscillation): (1) loop gain |Aβ| = 1, and (2) total phase shift around the loop = 0° or 360°. If gain > 1, oscillations grow; if < 1, they die.

4

RC oscillators use resistors and capacitors for the frequency-determining network. They work well for audio and low frequencies. Examples: Wien bridge, Phase-shift oscillator.

5

Wien bridge oscillator: uses a frequency-selective RC bridge. The op-amp provides gain while the bridge provides positive feedback at exactly one frequency.

6

Phase-shift oscillator: three RC sections each contributing 60° of phase shift (total 180° + 180° from inverting amplifier = 360°).

7

LC oscillators use an inductor-capacitor tank circuit which naturally oscillates at f = 1/(2π√(LC)). They work at high (radio) frequencies.

8

Hartley oscillator: the LC tank has a tapped inductor (two inductors in series). Widely used in AM radios.

9

Colpitts oscillator: the LC tank has a tapped capacitor (two capacitors in series). Better stability than Hartley.

10

Crystal oscillators use a quartz crystal whose mechanical resonance gives an extremely stable frequency. Used wherever precision matters: microprocessor clocks, GPS, mobile phones.

1

An amplifier takes a weak input signal and produces a stronger output signal of the same shape. It supplies the extra energy from its DC power supply.

2

Amplifiers are classified by conduction angle — how much of the input cycle the transistor is conducting.

3

Class A: conducts for the FULL 360° cycle. Best linearity (no distortion), but efficiency is low (~25–50%) because current flows even with no input.

4

Class B: each transistor in a push-pull pair conducts for only 180°. Higher efficiency (~78%), but has crossover distortion near zero-crossing where neither device conducts.

5

Class AB: conducts slightly more than 180°. A small bias keeps both transistors just barely on, eliminating crossover distortion while keeping efficiency reasonable.

6

Class C: conducts for LESS than 180°. Very high efficiency, but highly non-linear — only used in RF power amplifiers with a tuned LC load.

7

Push-pull configuration: one transistor handles the positive half-cycle, the other handles the negative half-cycle. Used in Class B and AB output stages.

8

Tuned (narrow-band) amplifier: uses an LC resonant circuit as the load — amplifies only signals near the resonant frequency. Used in radio receivers.

9

Operational Amplifier (op-amp): a high-gain differential amplifier IC with two inputs — inverting (−) and non-inverting (+).

10

Ideal op-amp characteristics: open-loop gain A → ∞, input impedance → ∞, output impedance → 0, bandwidth → ∞.

11

Virtual short principle: when negative feedback is applied, the op-amp drives its output to make both inputs at the same voltage. Simplifies circuit analysis enormously.

12

Common op-amp circuits: inverting amplifier, non-inverting amplifier, voltage follower (buffer), summing amplifier, integrator, differentiator, comparator.