WBBSE Madhyamik Electronics (Vocational) 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, expressed as V = I × R.

Electrical power formula

Power in watts equals voltage multiplied by current (P = V × I); it can also be written as I²R or V²/R for resistive circuits.

Parallel resistance rule

In a parallel network the voltage is the same across every branch, and the reciprocal of total resistance equals the sum of the reciprocals of individual resistances.

RMS value

The root-mean-square value of a sine wave equals the peak value divided by the square root of two, about 0.707 times the peak.

Resistor colour code

Bands give digits and a multiplier: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.

Capacitor code 104

The code 104 means 10 followed by four zeros, giving 100,000 picofarads, which equals 100 nanofarads or 0.1 microfarad.

Electrolytic capacitor polarity

Electrolytic capacitors are polarised; the marked negative stripe must go to the lower potential, and reversal can cause overheating, leakage, or explosion.

Inductor stored energy

An inductor stores energy in its magnetic field, given by half the inductance multiplied by the square of the current, and opposes sudden current changes.

Diode forward drop

A forward-biased silicon diode drops about 0.7 volts, while a germanium diode drops about 0.3 volts; reverse bias blocks current.

Zener diode operation

A Zener diode is reverse biased into breakdown to hold a nearly constant voltage, with a series resistor limiting current to a safe value.

BJT current gain

In a bipolar junction transistor the collector current equals the base current multiplied by beta, the forward current gain of the device.

BJT saturation region

In saturation both junctions are forward biased, the collector-emitter voltage falls to a small value, and the transistor behaves like a closed switch.

JFET control principle

A junction field-effect transistor is voltage controlled: the reverse-biased gate-source voltage sets the width of the channel and hence the drain current.

Bridge rectifier advantage

A bridge rectifier uses four diodes to give full-wave output at twice the supply frequency without needing a centre-tapped transformer secondary.

Ripple factor

Ripple factor is the ratio of the RMS value of the alternating component to the DC component of a rectifier output; smaller values mean smoother DC.

Common-emitter amplifier

A common-emitter stage gives voltage gain and current gain and inverts the signal, producing 180 degrees phase shift between input and output.

Oscillator condition

An oscillator needs positive feedback with loop gain at least one and a total loop phase shift of 360 degrees to sustain continuous output.

Binary to decimal

Convert binary to decimal by summing each bit multiplied by its place value, so 1011 equals 8 + 0 + 2 + 1, or 11.

De Morgan's theorems

De Morgan's laws state that the complement of a sum equals the product of complements, and the complement of a product equals the sum of complements.

Universal gates

NAND and NOR are called universal gates because either one alone can be wired to perform the AND, OR, and NOT functions.

Half adder outputs

A half adder adds two bits and produces a sum equal to their XOR and a carry equal to their AND.

Flip-flop versus combinational

A flip-flop is a sequential circuit that stores one bit and changes state on a clock edge, whereas combinational circuits produce outputs only from present inputs.

Multimeter connection rule

A multimeter goes in series with the circuit to measure current, in parallel to measure voltage, and across an unpowered component to measure resistance.

CRO voltage measurement

On an oscilloscope, peak voltage equals the volts-per-division setting multiplied by the number of vertical divisions the trace spans.

Good solder joint

A good solder joint is shiny, smooth, and cone shaped, formed by heating the joint and letting solder flow onto it rather than melting solder on the iron.

Three-terminal regulator 7805

The 7805 is a fixed linear regulator giving a 5 volt output; it needs an input a few volts higher and a heatsink at higher currents.

SMPS versus linear supply

A switch-mode power supply switches rapidly for high efficiency and low weight, while a linear supply is simpler and less noisy but bulkier and less efficient.

Repeated fuse blowing

If a replacement fuse of the correct rating blows again, a short circuit or overload exists in the appliance and must be found before further replacement.

RCCB function

A residual current circuit breaker trips when it detects a small imbalance between live and neutral currents, protecting people from earth leakage shock.

Electrical shock first aid

Switch off the supply or separate the victim using dry insulating material, then call emergency help and begin CPR if trained and breathing has stopped.

E-waste handling

Discarded electronics contain lead, mercury, and cadmium, so they must go to authorised recyclers and never be burned or dumped with household waste.

Service-shop job register

A job register records customer details, appliance, reported fault, parts replaced, charges, and warranty so that repairs can be traced and disputes avoided.