Karnataka KSEAB II PUC Electronics and Hardware (Vocational) flashcards

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

Resistor colour code

A four-band resistor encodes two significant digits, a decimal multiplier and a tolerance; colours run black 0 to white 9, with gold and silver as multipliers 0.1 and 0.01.

Capacitive reactance

The opposition a capacitor offers to alternating current, given by Xc = 1/(2πfC) in ohms. It falls as frequency or capacitance rises, and current leads voltage by 90 degrees.

Inductor energy storage

An inductor stores energy in its magnetic field as W = ½LI². Because voltage depends on di/dt, the current through an inductor cannot change instantly when a circuit switches.

Capacitor code 104

A ceramic capacitor marked 104 has a value of 10 followed by four zeros in picofarads, which is 100000 pF, equal to 100 nF or 0.1 microfarad.

Zener diode regulation

A Zener diode is reverse biased into its breakdown region, where it holds a nearly constant voltage. A series resistor drops the surplus input voltage and limits the current.

Bridge rectifier advantage

A bridge rectifier uses four diodes so that both half cycles conduct through the load without needing a centre-tapped transformer, giving full-wave output with ripple at twice line frequency.

Peak inverse voltage

The maximum reverse voltage a diode must withstand when not conducting. It is about Vm for half-wave and bridge rectifiers and about 2Vm for a centre-tap full-wave circuit.

LED forward voltage

The forward drop of a light-emitting diode depends on its semiconductor material: roughly 1.8 to 2.2 volts for red and 3.0 to 3.4 volts for blue or white devices.

Transistor current gain beta

For a bipolar transistor, beta is the dc ratio of collector current to base current, so Ic = beta times Ib. Alpha equals beta divided by beta plus one.

Transistor saturation region

With base current high enough, a transistor's collector-emitter voltage falls to about 0.2 volts and it behaves as a closed switch between collector and emitter.

JFET pinch-off voltage

The gate-source voltage at which a junction field-effect transistor's channel closes and drain current becomes almost zero, equal in magnitude to the pinch-off voltage Vp.

MOSFET gate insulation

An enhancement MOSFET has a thin oxide layer under its gate, so gate current is practically zero and the device is controlled purely by gate-source voltage above the threshold.

Barkhausen criterion

An oscillator sustains oscillation when the loop gain is at least one and the total phase shift around the feedback loop is zero or 360 degrees at the oscillation frequency.

Common-emitter phase inversion

A common-emitter amplifier produces a 180-degree phase shift between input and output, so a rising input voltage causes a falling collector voltage.

Decibel voltage gain

Voltage gain expressed in decibels equals 20 log(Vout/Vin). A gain of 10 is 20 dB, a gain of 0.707 is minus 3 dB, and doubling is about 6 dB.

Class B efficiency

A push-pull Class B stage conducts for 180 degrees per device and can reach about 78.5 percent theoretical efficiency, but suffers crossover distortion without bias.

Universal gates

NAND and NOR gates are called universal because either type alone can be wired to perform NOT, AND, OR and therefore any combinational logic function.

De Morgan theorems

Two Boolean identities: the complement of a product equals the sum of the complements, and the complement of a sum equals the product of the complements.

Half adder outputs

A half adder adds two single bits and produces Sum equal to A XOR B and Carry equal to A AND B; it cannot accept a carry from a previous stage.

J-K flip-flop toggle

When both J and K inputs are high, a J-K flip-flop changes state on every active clock edge, dividing the clock frequency by two at its output.

Ripple factor

The ratio of ac ripple voltage to dc output voltage in a supply. It is about 1.21 for half-wave and 0.482 for full-wave or bridge rectifiers before filtering.

Three-terminal regulator 7805

A fixed positive linear voltage regulator in the 78xx family that holds its output at 5 volts, provided the input stays a few volts higher and current and heating limits are respected.

Voltmeter connection

A voltmeter is connected in parallel with the component being measured and should have very high internal resistance so it draws negligible current and does not disturb the circuit.

Oscilloscope time base

The time/division control sets the horizontal sweep speed. Multiplying divisions spanned by one cycle by the time/division setting gives the waveform period.

Eutectic solder

A tin-lead alloy of 63 percent tin and 37 percent lead melts at a single temperature of 183 degrees Celsius, flowing cleanly and producing reliable hand-soldered joints.

Cold solder joint

A dull, grainy or ball-shaped joint formed when the parts were not heated sufficiently or moved while cooling; it has high resistance and causes intermittent faults.

Rosin flux function

A non-corrosive flux derived from pine resin that dissolves oxide films on pads and leads during soldering so molten solder wets the surfaces and forms an alloy bond.

Electrostatic discharge protection

Grounded wrist straps, earthed soldering irons and mats, and conductive foam storage prevent static charges from damaging sensitive CMOS and MOSFET inputs during handling.

Analog to digital conversion

An ADC converts a voltage into a binary number. With n bits and reference Vref, the step size is Vref divided by 2 to the power n.

Pulse width modulation

A switching technique that varies the fraction of time a signal stays high. Average output voltage equals duty cycle times supply voltage, controlling lamp brightness or motor speed.

I2C bus lines

A two-wire synchronous serial bus using serial data and serial clock lines, where each device has a seven-bit address and is identified by a master on the shared bus.

Light dependent resistor

A photoconductive sensor whose resistance falls as illumination increases, commonly used with a series resistor to form a voltage divider for light-sensing circuits.