Karnataka KSEAB SSLC NSQF Electronics and Hardware flashcards

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

Ohm's law

Voltage across a conductor equals current through it multiplied by resistance: V = I × R. Rearranged, I = V/R and R = V/I. Used to find any one unknown when two are known.

Resistors in parallel

Two resistors share the same voltage, so 1/R_total = 1/R1 + 1/R2, giving R_total = R1R2/(R1+R2). The result is always smaller than the smallest individual resistance in the network.

Electrical power formula

Power P = V × I, also written P = I²R or P = V²/R. It gives the heat dissipated by a component and determines the wattage rating a resistor needs for safe operation.

Kirchhoff's current law

At any node in a circuit, the total current entering equals the total current leaving. It expresses conservation of charge and is used to write node equations for circuit analysis.

RMS value of sine wave

The root-mean-square voltage or current equals the peak value divided by the square root of two, about 0.707 times peak. It is the effective value that produces the same heating as DC.

Resistor colour code

Digits are black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The third band is the multiplier and gold or silver marks tolerance.

Silicon diode forward drop

A conducting silicon diode drops about 0.7 V from anode to cathode, while a germanium diode drops about 0.3 V. In reverse bias the diode blocks current until its breakdown voltage.

Transistor saturation region

When base current is large enough, the transistor is fully on and the collector-emitter voltage falls to about 0.2 V. This region is used for switching loads such as relays and LEDs.

LED series resistor

The limiting resistor is R = (supply voltage − LED forward voltage) / desired LED current. For 5 V, 2 V LED and 15 mA, R equals 200 ohms, the nearest standard value being 220 ohms.

Zener diode regulation

A Zener diode is operated in reverse breakdown, where its voltage stays nearly constant over a current range. A series resistor drops the excess supply voltage and limits Zener current.

Electrolytic capacitor polarity

Electrolytic capacitors are polarised: the striped side is negative and the longer lead is positive. Reversed connection breaks down the oxide layer, causing heating, venting or explosion.

Good solder joint appearance

A sound joint is smooth, shiny and concave, wetting both pad and lead. Dull, grainy or ball-shaped solder indicates a cold joint caused by insufficient heat or contaminated surfaces.

Soldering iron tip temperature

Tin-lead solder works at about 300 to 350 degrees Celsius and lead-free solder at 350 to 380. Contact should be brief, about one to two seconds, to avoid damaging components.

Purpose of soldering flux

Flux chemically removes oxide films from the pad and lead so molten solder wets the metal. Residue from corrosive fluxes must be cleaned off to prevent leakage and corrosion.

Desoldering braid use

Solder wick is placed over the joint, heated with the iron, and absorbs molten solder by capillary action. It is used to remove bridges and to clear pads before fitting a replacement part.

PCB assembly order

Fit low-profile parts such as resistors and diodes first, then taller components like capacitors and connectors. Check polarity and value of each part before soldering it in place.

Solder bridge defect

A solder bridge is an unintended solder connection between two adjacent pads or tracks, shorting them. It is removed with desoldering braid and the joint is re-inspected before power is applied.

IC pin 1 identification

Pin 1 is marked by a notch, dot or chamfered corner on the package body. Correct orientation must be confirmed against the datasheet and board silkscreen before soldering the IC.

Voltmeter connection rule

A voltmeter is connected in parallel with the component being measured and has very high internal resistance. Connecting it in series with a load gives a near-zero current reading.

Ammeter connection rule

An ammeter is connected in series by breaking the circuit, and it has very low internal resistance. Connecting it directly across a supply causes a short circuit and may destroy the meter.

Continuity test mode

Continuity mode beeps when resistance is only a few ohms or less. It is a go/no-go check of tracks, fuses and cables, not a precision measurement, and requires a de-energised circuit.

Oscilloscope time base

The time/division control sets the horizontal scale, so the displayed period equals divisions multiplied by the time base. Its reciprocal gives the frequency of the observed waveform.

De Morgan's theorem

The complement of a product equals the sum of the complements, and the complement of a sum equals the product of the complements: (A·B)' = A' + B' and (A + B)' = A'·B'.

NAND as universal gate

The NAND gate outputs 0 only when all inputs are 1. Any logic function, including AND, OR and NOT, can be built using only NAND gates, so it is called a universal gate.

ADC resolution

Resolution equals reference voltage divided by two raised to the bit count. A 10-bit converter with a 5 V reference resolves about 4.9 millivolts per step, giving 1024 discrete levels.

Microcontroller reset circuit

The reset pin must be held at a defined level and released cleanly at power-up, usually with a resistor and capacitor or a supervisor IC. An unstable reset causes random program starts.

Signal tracing method

Inject a known signal at the input and follow it stage by stage with a meter or oscilloscope. The fault lies between the last point where the signal is correct and the first where it is not.

Supply rail under load

A supply rail that reads correct voltage with no load but collapses when loaded indicates a short, an overloaded output or a failing regulator with high internal resistance.

Bulged electrolytic capacitor

A domed or split top on an electrolytic capacitor shows internal gas pressure from ageing or overheating. It is a common cause of supply hum and must be replaced before further testing.

ESD wrist strap resistor

A wrist strap contains a one megohm series resistor that slowly bleeds static charge to earth. The resistor limits current if the wearer accidentally contacts a live conductor.

Electrical fire extinguisher choice

Carbon dioxide or dry powder extinguishers are used on live electrical fires because they do not conduct. Water must never be applied to energised equipment, as it conducts and causes shock.

Break-even quantity formula

Break-even quantity equals fixed costs divided by the difference between selling price and variable cost per unit. It gives the number of units that must be sold before the business makes a profit.