Electrical4U What is a Darlington Transistor? A Darlington transistor, or Darlington pair, combines two BJTs (Bipolar Junction Transistor) to provide high current gain. The emitter current of the first transistor drives the base of the second, so the pair needs much less input current than a single power BJT at the same collector current. The two-BJT … Read more
What are the Fresnel Equations? The Fresnel equations give amplitude reflection and transmission coefficients at a flat interface. Each coefficient is a ratio between the reflected or transmitted electric field amplitude and the incident amplitude, under a stated polarisation and sign convention. A complex coefficient describes relative amplitude and phase. These equations describe a plane … Read more
What is an Arduino? Arduino is an open-source electronics platform built around programmable development boards and software tools. Arduino IDE runs on Windows, macOS and Linux and uploads a program, commonly called a sketch, to the board. The project began at the Interaction Design Institute Ivrea in Italy to make electronics prototyping more accessible. Arduino … Read more
What is Radiometry? Radiometry measures radiant energy and related quantities without weighting them for human vision. In optical metrology, it covers ultraviolet, visible and infrared electromagnetic radiation. Photometry covers visible radiation and weights it by the standard response of human vision. The term radiometry is also used in radio and microwave measurement. Matter above absolute … Read more
What is a Rogowski Coil? A Rogowski coil is a non-magnetic-core current sensor for alternating current, pulses and transients within its specified bandwidth and peak rate-of-change limits. It is named after German physicist Walter Rogowski. Its sensing winding is distributed around a closed loop, with N turns and a controlled cross-section. The core former is … Read more
What is a Slip Ring? A slip ring is an electromechanical rotary interface that maintains electrical circuits between stationary and rotating structures. It can carry power , analogue signals or digital data during intermittent or continuous rotation. Other names include rotary electrical joint, rotating electrical connector and electrical swivel. A slip ring prevents fixed wiring … Read more
Physics studies matter, energy, motion, forces, fields, space and time through observation, experiment and mathematical models. Its scope ranges from subatomic particles to planets and galaxies. Quantum mechanics and relativity describe different physical regimes, while a complete theory that unifies quantum physics with gravity remains an open research goal. This category groups introductory articles on … Read more
What is DC Current? DC stands for direct current, so “DC current” is a common but redundant phrase. Direct current is the unidirectional flow of electric charge. Its magnitude may be steady or may vary without reversing polarity. In an alternating current circuit, polarity and current direction reverse periodically. Direct current can pass through a … Read more
What is Reactance? Reactance (also known as electrical reactance) describes the frequency-dependent opposition to sinusoidal current caused by inductance or capacitance. It affects current magnitude and phase for an applied voltage. Reactance and electric resistance are both measured in ohms. Ideal reactance represents energy storage, while ideal resistance represents average energy dissipation. In sinusoidal steady … Read more
What is Reflectance Reflectance is reflected radiant flux фr divided by incident radiant flux фi under specified spectral, polarisation and geometric conditions. The standard symbol is ρ; the alternative p shown here is a legacy typesetting error. \[ \rho = \frac{\phi_r}{\phi_i} \] Reflectance is a dimensionless ratio of the same radiant-flux quantity. It can vary … Read more