Electrical4U 
A cyclotron is a compact ion accelerator. Its working principle of a cyclotron is that ions spiral in a uniform magnetic field while a radio-frequency voltage across two Dees adds kinetic energy at each gap crossing. The orbit period is independent of speed in the non-relativistic limit, so a fixed radio frequency stays in step. … Read more
The conductor resistance test measures the DC resistance of copper or aluminium conductors. IS 10810-5 reports that value in ohms per kilometre at 20°C. For a given voltage, higher resistance means less current. Conductor size, construction, temperature and resistivity all change the reading. Cable standards compare the corrected value with a maximum in ohms per … Read more
The wrapping test checks whether aluminium wire used in power cables can wrap and unwrap around its own diameter without breaking. IS 10810-3 (1984) is the Indian cable method for that ductility check. A conductor that passes can take the torsion of stranding and installation without snapping. The pass rule in that method is simple: … Read more
The Substitution theorem says you may replace one branch by an equivalent source without changing the voltages and currents in the rest of a uniquely solved network. The usual replacements are a voltage source equal to that branch voltage, or a current source equal to that branch current. The same idea is used to prove … Read more
Millman’s theorem reduces parallel voltage or current sources to one equivalent source. Jacob Millman, an electrical engineering teacher, is the usual namesake. It applies to a parallel electrical circuit. The equivalent matches Thevenin’s Theorem and Norton’s Theorem on those branches, and it gives the voltage across a load and the current through it. The same … Read more
Wave-particle duality is the statement that light and matter both behave as waves and as particles. The Photoelectric effect, Compton scattering and Bohr’s model of atom showed light and other radiation as packets, or Quanta.Huygens’ principle and Young’s double-slit experiment showed the same light as a wave, not only a stream of particles. The interference … Read more
Current density is the current through a unit area of a conductor. That quantity is used throughout electrical engineering. Current Density in Metal Imagine a conductor with a cross-section of 2.5 square mm. If an electric potential causes a current of 3 A, the current density is 1.2 A/mm² (3/2.5). This assumes the current is … Read more
An electron volt is the energy one electron gains when it moves through 1 volt. Start from ordinary circuit power: the watt.W = VI, where V is the voltage and I is the current.Current (I) is charge per unit time, so instantaneous power is: Here q(t) is the charge transferred in time t. Energy then … Read more
A small amount of impurity to a semiconductor contributes free electrons or holes and so changes how the semiconductor conducts. That process is doping. A pentavalent donor (atoms with five valence electrons) replaces a host atom. Four valence electrons form bonds with neighbours. The fifth electron is only weakly bound and can become a free … Read more
Conductivity of a semiconductor is set by how many free carriers it has. Metals (conductors) have a high free-electron density and therefore a high conductance (and a low resistance). Insulators have very few free electrons. A semiconductor sits between those two densities, so its conductivity sits between a metal and an insulator. That is why … Read more