Punjab PSEB Matric NSQF Electronics flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's Law

The current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, written V = I × R with V in volts, I in amperes and R in ohms.

Electric Power Formula

Power dissipated equals voltage times current, P = V × I, which can be rewritten as I²R or V²/R when only two quantities are known. Unit is the watt.

Series Circuit Rule

Components connected end to end share the same current, the total resistance is the sum of individual resistances, and the supply voltage divides in proportion to each resistance.

Parallel Circuit Rule

Components connected across the same two nodes share the same voltage, the total current is the sum of branch currents, and total resistance is always smaller than the smallest branch resistance.

Resistor Colour Code

Colour bands give value digits and multiplier: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold and silver mark tolerance.

Capacitive Reactance

Opposition offered by a capacitor to alternating current, calculated as X_C = 1/(2πfC). It decreases as frequency or capacitance increases, so a capacitor blocks steady DC.

Inductive Reactance

Opposition offered by an inductor to alternating current, calculated as X_L = 2πfL. It increases with frequency, so an inductor opposes changing current and passes DC easily.

RC Time Constant

The product R × C in seconds, giving the time for a capacitor to charge to about 63.2 percent of supply voltage; after five time constants charging is practically complete.

Diode Forward Bias

Condition where the anode is more positive than the cathode by roughly 0.7 V for silicon or 0.3 V for germanium, allowing conventional current to flow with low resistance.

Bridge Rectifier

Four diodes arranged so both half cycles of AC are converted to pulsating DC, giving full-wave output with ripple frequency twice the supply frequency.

Transistor Current Relation

For a bipolar transistor the emitter current equals base current plus collector current, I_E = I_B + I_C, and collector current equals beta times base current.

Transistor Load Line

A straight line on the output characteristic joining cut-off at V_CE = V_CC and saturation at I_C = V_CC/R_C; the operating Q point lies on this line in the active region.

RMS Value of Sine

The effective value of a sinusoidal wave, equal to peak value divided by the square root of two, about 0.707 times peak; a 230 V mains supply is an RMS figure.

Universal Logic Gates

NAND and NOR gates, because either one alone can be wired to perform AND, OR and NOT functions, so complete digital circuits can be built from that single gate type.

Decimal to Binary Conversion

Divide the decimal number repeatedly by two, note each remainder, then read the remainders from last to first to obtain the binary equivalent, using 8 bits for one byte.

Ammeter Connection Rule

An ammeter must be connected in series with the circuit and has very low internal resistance, so it does not drop voltage or divert current from the measured branch.

Voltmeter Connection Rule

A voltmeter is connected in parallel across the component and has very high internal resistance, so it draws negligible current and reads the true potential difference.

Wattmeter Coil Arrangement

The current coil is connected in series with the load and the pressure or voltage coil in parallel across it; the meter deflection indicates real power in watts.

Continuity Test Procedure

With the circuit de-energised, select continuity or low-ohms mode; a buzzer or near-zero reading means a closed path, while overload display means an open circuit.

Cold Solder Joint

A dull, grainy or ball-shaped joint caused by insufficient heat or movement while cooling; it has high resistance and must be reheated and reflowed to a shiny concave fillet.

Soldering Iron Temperature

Typical tip temperature is 300 to 350 degrees Celsius for tin-lead solder and slightly higher for lead-free solder; the joint is heated first, then solder is fed in.

PCB Component Fitting Order

Solder low-profile parts such as resistors and diodes first, then capacitors and IC sockets, and finally tall components and connectors, checking polarity and orientation before each joint.

Electrolytic Capacitor Polarity

Electrolytic capacitors are polarised: the marked stripe identifies the negative lead. Reversing polarity can cause overheating, leakage or rupture, so the marking is checked before soldering.

IC Notch Orientation

The notch or dot on an integrated circuit marks pin 1; the socket and chip must align with the PCB outline, with pin numbers counted anticlockwise from that mark.

Oscilloscope Trigger Control

The trigger level and source stabilise the displayed waveform; without a correct trigger the trace drifts across the screen and period or amplitude cannot be measured reliably.

Oscilloscope Probe Compensation

A times-ten probe is adjusted with the calibration square wave until the corners are square; under- or over-compensation distorts amplitude and rise-time readings on the screen.

Half-Split Fault Finding

Test at the midpoint of the signal path, decide which half contains the fault, then halve again; this localises a fault in the fewest measurements instead of testing every part.

Power Supply Voltage Check

Measure in sequence: transformer secondary AC, rectifier DC, filter DC and regulator output. The first stage showing an incorrect value identifies the faulty block.

ESD Protection Practice

Use an antistatic wrist strap and grounded mat when handling CMOS or MOSFET devices, store chips in conductive foam, and never touch pins, since static discharge can destroy the gate oxide.

Filter Capacitor Discharge

Before servicing a power supply, unplug it and discharge large filter capacitors through a resistor; stored charge can remain at dangerous voltage even after the mains is removed.

Multimeter Range Selection

Select the correct function and a range above the expected value before connecting the probes; measuring voltage on the ohms range or current on the volts range can damage the meter.