Assam ASSEB HSLC 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

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

Series vs parallel resistance

Series resistances add directly (R1 + R2). For parallel resistances the reciprocals add, so two resistors give R1R2/(R1+R2), which is always smaller than the smallest resistor.

RMS value

The RMS value of a sine wave is the equivalent DC value that produces the same heating effect. It equals peak divided by √2, about 0.707 times the peak.

Resistor colour code

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 the fourth gives tolerance.

Electrolytic capacitor polarity

Electrolytic capacitors are polarized. The lead beside the stripe with minus signs is negative. Reversing polarity can make the capacitor overheat, vent or explode.

Identify diode cathode

On a diode the printed band marks the cathode, which corresponds to the bar of the circuit symbol. Current flows from anode to cathode when forward biased.

Eutectic solder 63/37

A 63 percent tin, 37 percent lead solder is eutectic: it melts and freezes at a single temperature of 183 degrees Celsius, giving fewer cold joints than 60/40 solder.

Good solder joint

A sound joint is shiny, smooth and concave, wetting both pad and lead. A dull, ball-shaped or grainy joint is a cold joint and should be reflowed.

Desoldering braid

A copper wick with flux that is placed over a joint and heated with the iron; capillary action draws molten solder into the braid, clearing the pad.

Ammeter connection

An ammeter has very low resistance and must be connected in series with the load. Connecting it across a supply creates a short circuit and can damage the meter.

Continuity test

The meter's continuity mode applies a small voltage and beeps when resistance is low. The component should be isolated, otherwise parallel paths give misleading readings.

Oscilloscope timebase

The timebase sets the horizontal scale in seconds per division. Combined with the vertical volts per division it lets you read the amplitude and period of a waveform.

Bridge rectifier ripple

A full-wave bridge rectifier with four diodes converts both half-cycles, so its ripple frequency is twice the mains frequency, 100 Hz for a 50 Hz supply.

7805 regulator

A three-terminal linear regulator giving a fixed plus 5 volts output. Its input must be at least about 2 to 3 volts higher, and a heatsink is needed at high current.

Lead-acid cell voltage

Each lead-acid cell is nominally 2 volts, so a 12 volt battery has six cells in series. A fully charged cell has specific gravity around 1.26 to 1.28.

Li-ion charging

Lithium-ion cells are charged by constant current then constant voltage to 4.2 volts per cell. They must never be shorted, punctured, or charged below zero degrees Celsius.

Universal gates

NAND and NOR are called universal gates because any other logic function, including AND, OR and NOT, can be built using only NAND gates or only NOR gates.

De Morgan's theorems

De Morgan states that 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'.

CMOS unused inputs

CMOS gate inputs have very high impedance and must never be left floating, because they pick up noise and cause excessive current. Tie unused inputs to supply or ground.

Microcontroller vs microprocessor

A microcontroller contains CPU, memory and peripherals on one chip for embedded control. A microprocessor contains only the CPU and needs external memory and interface chips.

ADC resolution

For an n-bit ADC the number of steps is 2 to the power n, and the resolution is Vref divided by that number. A 10-bit ADC on 5 volts gives about 4.9 mV per step.

PWM duty cycle

Pulse-width modulation switches a supply on and off rapidly. The average voltage equals duty cycle times supply voltage, which controls LED brightness and motor speed.

ATX 12 V rail colour

In an ATX power supply the yellow wires carry plus 12 volts, red plus 5 volts, orange plus 3.3 volts, black ground, and green is the power-on signal.

POST troubleshooting

When a PC fails power-on self-test, reseat RAM, check the CPU power connector and the display cable, and listen for beep codes before replacing parts.

Discharge SMPS capacitors

Large filter capacitors in a switched-mode supply can hold dangerous voltage after unplugging. Bleed them through a resistor or use a proper discharge tool before servicing.

Microwave capacitor hazard

The high-voltage capacitor and magnetron circuit in a microwave oven store lethal charge. Discharge the capacitor with an insulated probe and never work on it while energized.

ESD wrist strap

A wrist strap with a one-megohm resistor safely bleeds static charge from the body to ground while limiting current, protecting sensitive components from electrostatic discharge.

Lockout tagout

Before servicing, isolate the supply, lock the breaker, attach a warning tag, and verify the circuit is dead with a tester before touching conductors.

Electrical fire extinguisher

Water conducts electricity and must never be used on live electrical fires. Use carbon dioxide or dry powder extinguishers rated for electrical equipment.

Break-even quantity

The break-even quantity equals total fixed costs divided by the difference between selling price and variable cost per unit, the point where revenue equals total cost.

Active listening at work

Active listening means giving full attention, not interrupting, paraphrasing the speaker's message and asking clarifying questions, which reduces errors in technical instructions.

Resume essentials

A resume lists contact details, a short skills summary, education and experience in reverse chronological order, using measurable achievements rather than vague duties.