Tamil Nadu HSE First Year Basic Electronics Engineering 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 = IR, with V in volts, I in amperes and R in ohms.

Kirchhoff's current law

At any junction in a circuit, the algebraic sum of all currents entering and leaving equals zero; the total current entering a node equals the total current leaving it.

Resistance formula for a wire

R = ρL/A, where ρ is the material resistivity, L the length and A the cross-sectional area. Doubling the length doubles resistance; doubling the area halves it.

Resistor colour code

Colour bands give digit values: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Gold tolerance is plus or minus five percent.

Capacitive reactance

X_C = 1/(2πfC), the opposition a capacitor offers to alternating current. It falls as frequency or capacitance increases, so a capacitor blocks DC and passes high frequencies.

Inductive reactance

X_L = 2πfL, the opposition an inductor offers to alternating current. It rises with frequency, so an inductor passes DC and opposes rapid current changes.

Electrolytic capacitor polarity

An electrolytic capacitor is polarised: its marked negative lead must connect to the lower potential. Reversing the voltage breaks down the oxide layer and can burst the can.

Diode knee voltage

The forward voltage at which a diode begins conducting strongly: about 0.7 V for silicon and 0.3 V for germanium. Below this value the forward current is negligible.

Full-wave rectifier output

A full-wave rectifier converts both half cycles, giving ripple at twice the supply frequency, average output about 0.637 of peak, and ripple factor about 0.48.

Peak inverse voltage

The maximum reverse voltage a rectifier diode must withstand. It is about twice the peak supply voltage for half-wave and centre-tap circuits, and about the peak value for a bridge.

Zener diode regulator

A Zener diode operated in reverse breakdown holds a nearly constant voltage across its terminals, so with a series resistor it regulates a load against supply and load variations.

Transistor current gain beta

Beta is the DC common-emitter current gain, I_C divided by I_B. It relates to alpha by beta = alpha/(1 minus alpha), and typically ranges from 50 to 300.

Transistor active region

The operating region where the emitter-base junction is forward biased and the collector-base junction reverse biased. The transistor then behaves as an amplifier with output current proportional to input current.

Common-emitter amplifier

A transistor amplifier with the emitter common to input and output. It gives high voltage gain and moderate current gain, and inverts the signal, producing 180 degrees phase shift.

DC load line

A straight line on the output characteristic joining cut-off (V_CE = V_CC) and saturation (I_C = V_CC/R_C). The quiescent point must lie on it for correct amplifier bias.

JFET pinch-off voltage

The reverse gate-source voltage at which the conducting channel is fully closed and drain current falls to nearly zero. Drain current follows I_D = I_DSS(1 minus V_GS/V_P) squared.

Enhancement MOSFET

A field-effect transistor that conducts only when the gate-source voltage exceeds a threshold; with zero gate voltage it is off. Its insulated gate gives extremely high input resistance.

SCR latching action

A PNPN thyristor turns on when forward biased and a gate pulse is applied, then stays on even without gate current until anode current drops below the holding current.

Universal gates

NAND and NOR gates are called universal because any logic function, including AND, OR and NOT, can be built using only one of these gate types.

XOR gate

An exclusive-OR gate outputs 1 only when its inputs are different and 0 when they are equal. It forms the sum output of a half adder.

De Morgan's theorems

Two Boolean identities: the complement of A AND B equals A-complement OR B-complement, and the complement of A OR B equals A-complement AND B-complement.

Half adder

A combinational circuit adding two single bits. Its sum output is A XOR B and its carry output is A AND B; two half adders plus an OR gate make a full adder.

Virtual ground

In an inverting op-amp circuit with negative feedback, the inverting input sits at almost zero volts although not connected to earth, because the high gain forces it to match the earthed input.

Non-inverting amplifier gain

For an op-amp with input at the non-inverting terminal, closed-loop gain equals 1 + R_f/R_in. Output is in phase with input and input impedance is very high.

Op-amp slew rate

The maximum rate at which an op-amp output can change, quoted in volts per microsecond. It limits large-signal response at high frequency and causes output distortion if exceeded.

Shunt for ammeter range

A low resistance connected in parallel with a moving-coil meter to carry most of the current. Its value is meter resistance divided by (multiplying factor minus one).

CRO time base

The internal sawtooth generator that sweeps the electron beam horizontally at a known rate, letting the screen display voltage against time so period and frequency can be measured.

Lissajous frequency measurement

When sine waves feed both CRO channels, the pattern's tangency counts give the frequency ratio: f_y/f_x equals horizontal tangencies divided by vertical tangencies.

Amplitude modulation index

The ratio of modulating voltage to carrier voltage, m = V_m/V_c. Values above one mean overmodulation, causing envelope distortion and unwanted sideband splatter.

Superheterodyne receiver

A receiver that mixes the incoming signal with a local oscillator to produce a fixed intermediate frequency, typically 455 kHz for AM, before detection and audio amplification.

Cold solder joint

A dull, rounded, poorly wetted joint caused by too little heat or contaminated surfaces. It has high resistance and intermittent contact, and must be reheated and resoldered.

Rosin flux function

A mild resin flux that dissolves oxide films and lowers surface tension so molten solder wets copper and component leads. Its residue is non-corrosive and need not be removed.