Tamil Nadu HSE Second Year Basic Electrical Engineering flashcards

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

Ohm's law

For a metallic conductor at constant temperature, current is directly proportional to applied voltage: V = IR, where R is resistance in ohms.

Kirchhoff's current law

The algebraic sum of all currents entering and leaving a node is zero, because charge cannot accumulate at a junction in a steady circuit.

Terminal voltage

The voltage actually available at a source's terminals, equal to EMF minus the internal voltage drop Ir, so it falls as load current increases.

Maximum power transfer

A source delivers maximum power to a load when load resistance equals source internal resistance; efficiency at that condition is only fifty percent.

Coulomb's law

The force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation.

Capacitance formula

C = Q/V in farads; for a parallel-plate capacitor C = ε₀ε_rA/d, so capacitance rises with plate area and dielectric constant and falls with spacing.

RC time constant

The product RC in seconds; after one time constant a charging capacitor reaches 63.2 percent of its final voltage, and after five it is essentially charged.

Capacitors in series

Reciprocals of capacitance add, so total capacitance is less than the smallest individual value, and every series capacitor carries the same charge.

Faraday's law of induction

The EMF induced in a coil equals the negative rate of change of flux linkage, e = −N dΦ/dt; a steady flux induces no EMF.

Lenz's law

The direction of an induced current is such that its magnetic effect opposes the change in flux that produced it, explaining the minus sign in Faraday's law.

Fleming's left-hand rule

With thumb, forefinger and middle finger mutually at right angles showing force, field and current, it gives the direction of force on a current-carrying conductor.

Reluctance

The opposition a magnetic circuit offers to flux, analogous to resistance; it increases with path length and decreases with core area and permeability.

RMS value

The square root of the mean of the squared instantaneous values; for a sine wave it equals peak divided by root two, about 0.707 of peak.

Power factor

The cosine of the phase angle between voltage and current; it equals R/Z in a series circuit, and true power is VI cos φ.

Series resonance

The condition in an RLC series circuit where inductive and capacitive reactances cancel, giving minimum impedance equal to R and unity power factor at f = 1/(2π√LC).

Star and delta relations

In star, line voltage is root three times phase voltage and line current equals phase current; in delta, line current is root three times phase current.

Transformer EMF equation

E = 4.44 f N Φm, so induced EMF per turn depends on frequency and maximum core flux; voltage ratio equals the turns ratio.

Transformer iron loss

Hysteresis plus eddy-current loss in the core; it is nearly constant at fixed voltage and frequency and is measured by the open-circuit test.

Back EMF of DC motor

The EMF induced in the armature opposing supply voltage, E_b = V − I_aR_a; it limits armature current and falls when the motor slows under load.

Synchronous speed

The speed of the rotating field, N_s = 120f/P revolutions per minute, where f is supply frequency and P the number of poles.

Induction motor slip

The fractional difference between synchronous speed and rotor speed, s = (N_s − N)/N_s; rotor frequency equals slip times supply frequency.

Earthing purpose

Connecting exposed metalwork to earth so fault current flows through the earth path and operates the fuse or ELCB instead of passing through a person.

ELCB or RCCB

A device that trips when the difference between phase and neutral current exceeds its sensitivity, typically 30 milliamperes, protecting people from earth leakage.

Two-way switch control

Two two-way switches connected by two strapping wires let a lamp be switched from either of two positions; an intermediate switch extends control to more positions.

Moving-coil instrument

An instrument whose coil rotates in a permanent magnetic field; it reads average value, works on DC, and is adapted for AC with a rectifier.

Megger

An insulation resistance tester that applies a high DC test voltage and reads resistance in megohms, revealing moisture, dirt or failed insulation.

Ammeter shunt

A low resistance connected in parallel with a moving-coil movement to bypass most current, extending the ammeter's range while keeping full-scale deflection.

Lead-acid cell voltage

A fully charged lead-acid cell gives about 2 volts on load; electrolyte is dilute sulphuric acid with specific gravity near 1.28 when charged.

Full-wave rectifier ripple

A full-wave or bridge rectifier produces two output pulses per supply cycle, so ripple frequency is twice the supply frequency, easing filtering.

Zener diode regulation

Operated in reverse breakdown, a zener holds a nearly constant voltage across its terminals, providing a stable reference when fed through a series resistor.

High-voltage transmission

Transmitting at high voltage reduces current for a given power, cutting I²R line loss and conductor size, which is why step-up transformers are used.

Illuminance

Luminous flux incident per unit area, measured in lux, where one lux equals one lumen per square metre of illuminated surface.