Electrical Engineering Cheat Sheet

The core ideas of Electrical Engineering distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Ohm's Law

The fundamental relationship stating that the voltage across a conductor is directly proportional to the current flowing through it, expressed as $V = IR$. This law is the cornerstone of circuit analysis and is used to predict how electrical components behave under different conditions.

Kirchhoff's Laws

Two circuit analysis principles: Kirchhoff's Current Law (KCL) states that all currents entering a node must sum to zero, and Kirchhoff's Voltage Law (KVL) states that all voltages around any closed loop must sum to zero. Together they enable systematic analysis of complex circuits.

Alternating Current (AC) vs. Direct Current (DC)

DC flows in one constant direction, as from a battery, while AC periodically reverses direction, as in household power outlets. AC is preferred for long-distance power transmission because transformers can easily step its voltage up or down, minimizing energy loss.

Impedance

The generalization of resistance to AC circuits, impedance accounts for both resistive and reactive (capacitive and inductive) opposition to current flow. It is expressed as a complex number with magnitude and phase angle, measured in ohms.

Semiconductor Physics

Semiconductors are materials whose electrical conductivity falls between conductors and insulators. By doping them with impurities to create p-type and n-type regions, engineers build diodes, transistors, and integrated circuits that form the basis of all modern electronics.

Electromagnetic Induction

Discovered by Michael Faraday, this principle states that a changing magnetic field through a conductor induces an electromotive force (voltage). It is the operating principle behind electric generators, transformers, and induction motors.

Signal Processing

The analysis, manipulation, and synthesis of signals such as audio, video, and sensor data. Techniques include filtering, Fourier transforms, modulation, and compression, applied in both analog and digital domains.

Feedback and Control Systems

Control systems use feedback loops to maintain a desired output despite disturbances. A sensor measures the output, a controller compares it to the setpoint, and an actuator adjusts the system accordingly. Stability analysis ensures the system does not oscillate or diverge.

Power Systems and the Electric Grid

Power systems engineering deals with the generation, transmission, distribution, and utilization of electric power on a large scale. The grid must balance supply and demand in real time while maintaining stable frequency and voltage levels.

Digital Logic and Microprocessors

Digital logic uses binary states (0 and 1) implemented with transistor-based logic gates (AND, OR, NOT) to perform computation. Millions of these gates are combined in microprocessors that execute programmed instructions at billions of operations per second.

Key Terms at a Glance

Voltage:The electric potential difference between two points, measured in volts (V). It represents the energy per unit charge available to drive current through a circuit.

Current:The rate of flow of electric charge past a point in a circuit, measured in amperes (A). Conventional current flows from positive to negative, while electron flow is in the opposite direction.

Resistance:The opposition to the flow of electric current in a material, measured in ohms. It converts electrical energy into heat according to Joule's Law ($P = I^2R$).

Capacitance:The ability of a component to store electric charge, measured in farads (F). A capacitor with higher capacitance stores more charge at a given voltage ($Q = CV$).

Inductance:The property of a conductor by which a change in current induces an EMF in itself or a nearby conductor, measured in henrys (H). It opposes changes in current flow.

Reactance:The opposition to current flow from capacitors or inductors in an AC circuit, measured in ohms. Capacitive reactance decreases with frequency; inductive reactance increases with frequency.

Diode:A two-terminal semiconductor device that allows current to flow primarily in one direction. It is based on a p-n junction and is used in rectification, voltage regulation, and signal demodulation.

Transistor:A semiconductor device used to amplify or switch electronic signals and power. The two main types are BJTs (current-controlled) and MOSFETs (voltage-controlled).

MOSFET:Metal-Oxide-Semiconductor Field-Effect Transistor, the most widely used transistor type in digital and analog circuits. Its gate voltage controls current between source and drain terminals.

Operational Amplifier:A high-gain voltage amplifier with differential inputs and a single output. With feedback, it performs precise amplification, filtering, integration, and other signal processing functions.

Transformer:A device that transfers electrical energy between two or more circuits through electromagnetic induction, allowing voltage to be stepped up or down according to the turns ratio.

Rectifier:A circuit that converts AC to DC using diodes. Common types include half-wave (one diode) and full-wave bridge (four diodes) rectifiers.

Filter:A circuit that selectively passes or blocks certain frequency ranges from a signal. Types include low-pass, high-pass, band-pass, and band-stop (notch) filters.

Frequency Response:A characterization of how a system responds to different input frequencies, typically plotted as gain and phase versus frequency on a Bode plot.

Bode Plot:A graphical representation of a system's frequency response using two plots: magnitude (in dB) and phase (in degrees) versus frequency on a logarithmic scale.

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