MPPSC SES Electrical flashcards

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

Thevenin's Theorem

Any linear two-terminal network can be replaced by a single voltage source V_th equal to the open-circuit voltage, in series with R_th measured with all independent sources deactivated.

Maximum Power Transfer

A source delivers maximum power to a load when the load resistance equals the Thevenin resistance; for AC networks the load impedance must be the complex conjugate of the source impedance.

Series RLC Resonance

Resonance occurs when inductive and capacitive reactances are equal, giving f₀ = 1/(2π√(LC)); impedance is then purely resistive and current is at its maximum.

Transformer EMF Equation

The RMS induced EMF is E = 4.44 f N Φ_max, where f is supply frequency, N is turns, and Φ_max is the peak core flux in webers.

Induction Motor Slip

Slip s = (N_s − N_r)/N_s, where N_s = 120f/P is synchronous speed and N_r is rotor speed; rotor frequency equals slip times supply frequency.

Synchronous Machine Power Angle

Real power delivered by a round-rotor synchronous generator is P = (EV/X_s) sin δ, where δ is the load angle between internal EMF and terminal voltage.

Surge Impedance Loading

Surge impedance is Z_c = √(L/C), roughly 400 ohms for overhead lines; SIL equals V_L²/Z_c and indicates the load at which reactive losses balance charging.

Ferranti Effect

On a long transmission line carrying little or no load, the receiving-end voltage rises above the sending-end voltage because line capacitance supplies charging current through the series inductance.

Symmetrical Components

Unbalanced three-phase phasors are resolved into positive, negative, and zero sequence sets; zero-sequence currents require a return path through neutral or earth.

Routh-Hurwitz Criterion

The number of sign changes in the first column of the Routh array equals the number of closed-loop poles in the right half of the s-plane.

Phase Margin

Phase margin is 180° plus the open-loop phase at the gain crossover frequency; it measures relative stability and typically should exceed 45 degrees.

SCR Latching Current

The minimum anode current required to keep an SCR conducting immediately after the gate pulse is removed; below the lower holding current it turns off.

Buck Converter Duty Cycle

For an ideal buck chopper the output voltage is V_o = D·V_s, where D is the on-time fraction of the switching period; the output is always lower than the input.

Induction Motor V/f Control

Keeping the voltage-to-frequency ratio constant maintains air-gap flux approximately constant, so the motor can deliver rated torque at variable speed below base speed.

Two-Wattmeter Method

In a balanced three-phase load, total power is W₁ + W₂ and the power factor angle satisfies tan φ = √3(W₁ − W₂)/(W₁ + W₂).

Current Transformer Safety

A CT secondary must never be open-circuited while primary current flows, because the resulting high secondary voltage can destroy insulation and endanger personnel.

Wheatstone Bridge Balance

The bridge is balanced when the galvanometer reads zero and R_x = R₂R₃/R₁; balance is independent of the applied voltage magnitude.

Op-Amp Virtual Short

With negative feedback and ideal infinite gain, the inverting and non-inverting input voltages are forced equal, although no physical connection exists between them.

De Morgan's Theorems

The complement of a product equals the sum of the complements, and the complement of a sum equals the product of the complements: (AB)' = A' + B'.

Successive Approximation ADC

This ADC compares the input against a trial voltage set bit by bit from the most significant end, achieving n-bit conversion in n clock cycles.

8085 Multiplexed Bus

The 8085 uses pins AD0–AD7 for both the low-order address and the data bus, so an external latch such as the 74LS373 separates them.

8051 Reset Vector

After reset, the 8051 program counter loads 0000H and execution begins there; interrupt vectors occupy fixed low addresses at intervals of eight bytes.

I2C Bus

A two-wire synchronous serial bus using SDA and SCL lines, with 7-bit device addressing and acknowledgement bits; multiple devices share the same bus.

Nyquist Sampling Theorem

A band-limited signal with maximum frequency f_max can be reconstructed exactly if sampled at a rate of at least 2f_max; lower rates cause aliasing.

AM Modulation Index

The ratio m = V_m/V_c of modulating to carrier amplitude; values above unity cause overmodulation and envelope distortion, while m = 1 gives maximum undistorted modulation.

Shannon Channel Capacity

The maximum error-free data rate is C = B log₂(1 + S/N) bits per second, where B is bandwidth and S/N is the linear signal-to-noise power ratio.

Paschen's Law

The breakdown voltage of a uniform gas gap is a function of the product of pressure and gap length, showing a minimum at a particular pd value.

Faraday's Law of Induction

The EMF induced in a circuit equals the negative rate of change of magnetic flux linkage; the negative sign expresses Lenz's law.

Illuminance Inverse-Square Law

Illuminance on a surface perpendicular to the light direction is E = I/d², where I is luminous intensity in candela and d is distance in metres.

Tractive Effort

The force needed to move a train equals the sum of resistance to motion plus the force for acceleration, limited by adhesive weight times adhesion coefficient.

Whistleblowing Conditions

Disclosure outside the organisation is ethically defensible when a serious public danger exists, internal reporting has failed, and the engineer has documented evidence.