Punjab PSEB Matric NSQF Electronics cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. In series circuits current is common and resistances add; in parallel voltage is common and conductances add (1/R_T = 1/R1 + 1/R2 + …).

Resistor colour code: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9; gold tolerance ±5%, silver ±10%, no band ±20%. Third band is the multiplier, fourth band tolerance.

Capacitor charge Q = C × V; energy E = ½CV²; reactance X_C = 1/(2πfC) falls as frequency rises. Capacitors block DC and pass AC; inductors do the opposite with X_L = 2πfL.

Time constant τ = R × C for an RC circuit; one τ charges to 63.2% of final voltage, five τ is treated as full charge/discharge. For RL circuits τ = L/R.

Semiconductor diode: forward biased when anode is positive by more than ~0.7 V (Si) or ~0.3 V (Ge); reverse biased blocks current. A bridge rectifier gives full-wave DC, ripple frequency 2f, and needs four diodes.

Transistor basics: NPN conducts when base is ~0.7 V above emitter; relation I_E = I_B + I_C with I_C = β × I_B. DC load line joins V_CE = V_CC (cut-off) and I_C = V_CC/R_C (saturation); Q point sits on the active-region load line.

Binary and logic: decimal-to-binary by repeated division by 2; 1 byte = 8 bits. Basic gates: AND (output 1 only if all inputs 1), OR (1 if any input 1), NOT (inverter); NAND and NOR are universal gates.

AC quantities: RMS = peak/√2 ≈ 0.707 × peak; average of full sine = 0.637 × peak; frequency f = 1/T. In a purely resistive circuit current and voltage are in phase; in a purely inductive circuit current lags by 90°.

Instrument rules: ammeter in series with low resistance; voltmeter in parallel with high resistance; wattmeter has current coil in series and pressure coil in parallel; multimeter on the correct range before probing a live circuit.

Resistor measurement: isolate the component or de-energise the board before using a DMM on the ohms range; measured value must lie inside the colour-code tolerance band, e.g. 4.7 kΩ ±5% means 4.465–4.935 kΩ.

Continuity testing: use the buzzer/continuity mode on a dead circuit only; a good fuse, switch contact or track reads near 0 Ω, while an open circuit reads overload (OL).

Soldering rule of thumb: iron tip 300–350 °C for Sn-Pb solder (higher for lead-free), heat the joint then feed solder, shiny concave fillet is good, dull grainy joint is a cold joint and must be reflowed.

PCB assembly order: fit and solder lowest-profile parts first (resistors, diodes, IC sockets), then capacitors, then connectors and tall components; observe diode band, IC notch and electrolytic polarity before soldering.

Power-supply check sequence: inspect for shorts and polarity, then measure transformer secondary AC, rectifier DC, filter DC and finally regulator output; a low or zero rail points to the regulator, bridge or fuse, not the load.

Oscilloscope use: set probe ×10 with compensation, connect ground clip first, set vertical scale in V/div and time base in ms/div, then adjust trigger level for a stable trace; measure peak-to-peak and period from the graticule.

ESD and safety: wear an antistatic wrist strap when handling CMOS and MOSFET devices, never touch pins; treat any mains-side circuit as live, use an isolation transformer, and discharge filter capacitors before servicing.

Fault-finding decision rule: divide-and-measure from the middle of the signal path (half-split method) - compare expected DC voltages and signal levels against the schematic to localise the faulty stage before replacing parts.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. In series circuits current is common and resistances add; in parallel voltage is common and conductances add (1/R_T = 1/R1 + 1/R2 + …).

Resistor colour code: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9; gold tolerance ±5%, silver ±10%, no band ±20%. Third band is the multiplier, fourth band tolerance.

Capacitor charge Q = C × V; energy E = ½CV²; reactance X_C = 1/(2πfC) falls as frequency rises. Capacitors block DC and pass AC; inductors do the opposite with X_L = 2πfL.

Time constant τ = R × C for an RC circuit; one τ charges to 63.2% of final voltage, five τ is treated as full charge/discharge. For RL circuits τ = L/R.

Semiconductor diode: forward biased when anode is positive by more than ~0.7 V (Si) or ~0.3 V (Ge); reverse biased blocks current. A bridge rectifier gives full-wave DC, ripple frequency 2f, and needs four diodes.

Transistor basics: NPN conducts when base is ~0.7 V above emitter; relation I_E = I_B + I_C with I_C = β × I_B. DC load line joins V_CE = V_CC (cut-off) and I_C = V_CC/R_C (saturation); Q point sits on the active-region load line.

Binary and logic: decimal-to-binary by repeated division by 2; 1 byte = 8 bits. Basic gates: AND (output 1 only if all inputs 1), OR (1 if any input 1), NOT (inverter); NAND and NOR are universal gates.

AC quantities: RMS = peak/√2 ≈ 0.707 × peak; average of full sine = 0.637 × peak; frequency f = 1/T. In a purely resistive circuit current and voltage are in phase; in a purely inductive circuit current lags by 90°.

Instrument rules: ammeter in series with low resistance; voltmeter in parallel with high resistance; wattmeter has current coil in series and pressure coil in parallel; multimeter on the correct range before probing a live circuit.

Resistor measurement: isolate the component or de-energise the board before using a DMM on the ohms range; measured value must lie inside the colour-code tolerance band, e.g. 4.7 kΩ ±5% means 4.465–4.935 kΩ.

Continuity testing: use the buzzer/continuity mode on a dead circuit only; a good fuse, switch contact or track reads near 0 Ω, while an open circuit reads overload (OL).

Soldering rule of thumb: iron tip 300–350 °C for Sn-Pb solder (higher for lead-free), heat the joint then feed solder, shiny concave fillet is good, dull grainy joint is a cold joint and must be reflowed.

PCB assembly order: fit and solder lowest-profile parts first (resistors, diodes, IC sockets), then capacitors, then connectors and tall components; observe diode band, IC notch and electrolytic polarity before soldering.

Power-supply check sequence: inspect for shorts and polarity, then measure transformer secondary AC, rectifier DC, filter DC and finally regulator output; a low or zero rail points to the regulator, bridge or fuse, not the load.

Oscilloscope use: set probe ×10 with compensation, connect ground clip first, set vertical scale in V/div and time base in ms/div, then adjust trigger level for a stable trace; measure peak-to-peak and period from the graticule.

ESD and safety: wear an antistatic wrist strap when handling CMOS and MOSFET devices, never touch pins; treat any mains-side circuit as live, use an isolation transformer, and discharge filter capacitors before servicing.

Fault-finding decision rule: divide-and-measure from the middle of the signal path (half-split method) - compare expected DC voltages and signal levels against the schematic to localise the faulty stage before replacing parts.