Electrical4U 
A high pressure sodium vapor lamp is a high-intensity discharge lamp in which an electric arc excites sodium vapour. HPS lamps became common in road, area and industrial lighting because mature products offered high luminous efficacy and long rated life. Many installations now use LEDs, but HPS systems remain in service. What is a High … Read more
The Seebeck effect is the production of electric voltage by a temperature difference across a conductor or circuit. The reverse conversion, in which electric current moves heat, is the separate Peltier effect. Thomas Johann Seebeck reported the voltage effect in 1821. It underpins thermocouples and thermoelectric generators, while related spin-dependent effects are studied in spin … Read more
A motor protection system detects abnormal electrical, thermal or mechanical conditions and disconnects or controls the motor before damage becomes unacceptable. The scheme must also protect conductors and switching equipment and reduce hazards to people and the driven machine. This article outlines common faults, the separate roles of motor protection devices and the main selection … Read more
What is a silicon semiconductor? A silicon semiconductor is elemental silicon whose electrical conductivity lies between that of a conductor and an insulator. Crystalline silicon is an indirect-band-gap semiconductor with a band gap of about 1.12 eV at room temperature. Manufacturers control its carrier concentration and conductivity through doping, electric fields and light, which makes silicon useful … Read more
Valence electrons help explain chemical bonding, while electrical conductivity describes how charge moves through a material. The two ideas are related, but an atom’s valence-electron count does not by itself determine whether a solid is a conductor, semiconductor or insulator. The material’s energy bands, available charge carriers and structure also matter. What is a Valence … Read more
A carbon composition resistor is a fixed resistor with a moulded bulk element made from carbonaceous particles, filler and binder. Changing the composition changes bulk resistivity and therefore the relation between applied voltage and electric current. Carbon and binder together form one resistive path, with properties between a perfect conductor and a perfect insulator. End … Read more
What is a Steam Condenser for a Turbine? A steam condenser removes heat from the low-pressure exhaust of a steam turbine and returns the steam to liquid water. Maintaining a low condensing pressure reduces backpressure on the steam turbine and lets it extract more work. Water-cooled surface condensers are common, but direct-contact and air-cooled arrangements also exist. … Read more
Fluorescent lamps have been used in homes, offices, schools and industrial buildings. They are usually more efficient and longer-lived than incandescent lamps, although the lamp and ballast determine actual performance. An electric current excites low-pressure mercury vapour, producing strong ultraviolet emission near 254 nm. The inner phosphor layer converts much of that UV energy into … Read more
A photoelectron is an electron emitted after a material, atom or molecule absorbs a photon. In the external photoelectric effect, the electron leaves a surface. Measurements of the threshold and electron energy helped establish that light transfers energy in discrete quanta. This article explains the basic surface experiment and distinguishes it from related light-driven processes. … Read more
What is Electrical Polarity? Electrical polarity assigns positive and negative reference labels to two terminals. Voltage is the potential difference measured between those references, so reversing the labels reverses the voltage sign. Circuit diagrams use two polarity labels: An isolated object with more electrons than protons has net negative charge; one with fewer electrons has … Read more