RRB JE CBT 2 Electrical flashcards

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

Ohm's Law

For a linear conductor at constant temperature, current is directly proportional to voltage and inversely proportional to resistance: V = I × R.

Kirchhoff's Current Law

The algebraic sum of currents entering a node is zero; equivalently, total current entering equals total current leaving, based on conservation of charge.

Thevenin's Theorem

Any linear two-terminal network can be replaced by an equivalent voltage source Vth in series with Rth, where Vth is open-circuit voltage and Rth is resistance seen with sources killed.

Maximum Power Transfer

A load receives maximum power from a source when load resistance equals source (Thevenin) resistance. Maximum power is Vth²/(4Rth) and efficiency is 50%.

RMS Value

Root-mean-square value of a sinusoidal waveform equals peak value divided by √2 (≈0.707 × peak). It represents the equivalent DC value for heating effect.

DC Motor Back EMF

In a DC motor, back emf Eb = V − IaRa opposes the applied voltage and limits armature current. It is proportional to speed and flux.

Transformer EMF Equation

Induced emf per winding is E = 4.44 f N Φm, where f is frequency, N is turns, and Φm is maximum flux. Voltage per turn is constant in both windings.

Induction Motor Slip

Slip s = (Ns − Nr)/Ns, where Ns is synchronous speed and Nr is rotor speed. Rotor frequency equals slip times supply frequency, and rotor emf is sE2.

Synchronous Speed

Speed of rotating magnetic field: Ns = 120f/P rpm, where f is supply frequency in Hz and P is number of poles. Synchronous motors run exactly at this speed.

Surge Impedance

For a lossless transmission line, surge impedance Zc = √(L/C). Surge impedance loading (SIL) = V²/Zc gives power at unity power factor with flat voltage profile.

Corona Effect

Ionisation of air around high-voltage conductors when surface voltage gradient exceeds about 30 kV/cm peak, causing power loss, ozone, and radio interference.

Buchholz Relay

A gas-operated protective relay installed in the pipe between transformer tank and conservator; it detects incipient faults producing gas and severe faults causing oil surge.

Two-Wattmeter Method

Measures total three-phase power as W1 + W2. Power factor angle φ = tan⁻¹[√3(W1 − W2)/(W1 + W2)]. If W1 = W2, power factor is unity.

Wheatstone Bridge

A four-arm bridge balanced when R1/R2 = R3/R4, used to measure medium resistance. At balance, no current flows through the galvanometer.

LVDT

Linear Variable Differential Transformer: a displacement transducer with one primary and two secondary windings; output differential voltage is proportional to core displacement.

SCR Turn-Off

A thyristor stops conducting when anode current falls below holding current. Natural commutation occurs at AC zero crossing; forced commutation uses external circuit.

Buck Chopper

A step-down DC-DC converter whose average output voltage equals duty cycle times input voltage (Vout = D × Vin), with D between 0 and 1.

V/f Control

Variable-frequency induction motor drive maintains constant voltage-to-frequency ratio to keep air-gap flux constant, allowing speed control without saturation.

Routh-Hurwitz Criterion

A method to determine stability from the characteristic equation: the number of sign changes in the first column of the Routh array equals the number of right-half-plane poles.

Illuminance

Luminous flux incident per unit area, measured in lux (lm/m²). It follows the inverse square law E = I/d² and Lambert's cosine law E = (I cos θ)/d².

Traction DC Series Motor

Preferred for traction because it develops high starting torque and its speed decreases with load, providing inherent self-regulating characteristic for train movement.

Zener Diode

A heavily doped PN junction diode operated in reverse breakdown to provide a stable reference voltage; used in voltage regulators and clippers.

Op-Amp Inverting Amplifier

An operational amplifier circuit with input through Rin to inverting terminal and feedback Rf; voltage gain = −Rf/Rin, with 180° phase inversion.

De Morgan's Theorems

Boolean identities: (A·B)' = A' + B' and (A + B)' = A'·B'. They allow conversion between AND and OR forms using inversion.

8085 Microprocessor

An 8-bit microprocessor with 16-bit address bus (64 KB memory) and 8-bit data bus; it has maskable interrupts and a non-maskable TRAP interrupt.

Indian Railway Zones

Indian Railways is administratively divided into zones (currently 18), each headed by a General Manager and further divided into divisions under a Divisional Railway Manager.

National Science Day

Celebrated on 28 February in India to commemorate the discovery of the Raman effect by Sir C. V. Raman on that date in 1928.

Syllogism

A logical reasoning problem with statements and conclusions; conclusions are valid only if they follow from all possible Venn diagram representations of the statements.

Clock Angle Formula

Angle between hour and minute hands = |30H − 5.5M| degrees, where H is hour and M is minutes. A negative result is taken as absolute value.

Compound Interest

Interest calculated on principal plus accumulated interest: CI = P[(1 + R/100)^T − 1]. For half-yearly compounding, use R/2 and 2T.

Alligation Rule

To mix two ingredients at prices c and d to get mean price m, the ratio of quantities is (d − m):(m − c), where c < m < d.

Road Safety Signal

Traffic light rules: red means stop, yellow means wait/prepare to stop, green means go. Always wear helmet/seat belt and avoid mobile phone use while driving.

25 kV AC Traction

Indian Railways uses 25 kV, 50 Hz single-phase AC overhead equipment for electric traction, with current returning through the rails to the traction substation.