Electrical Circuits

Electrical Charges: Electrical charges come as plus or minus. Like charges repel, unlike charges attract. Electrons and protons have, to fantastic accuracy, equal and opposite charges. Quarks have 1/3 the electron charge but are never seen alone! In wires electrons do the moving to carry electrical current. In solutions or plasmas there can be positive charge carriers, ions or protons. Although the signal to tell electrons to move in wires travels at about 2/3 the speed of light (FAST in laymen's terms) the electrons only travel at a person's walking pace! Circuits: Electrical circuits are designed to take energy from a power supply (battery, generator, alternator, solar cell, thermocouple, fuel cell, . . .) and ultimately deliver the energy to an output (heater, light, motor, TV, computer monitor, speakers, . . .). In some cases the energy is the important part (heaters, motors) in other cases it is the information carried and manipulated by the circuit that is the useful output (telephone, cellular phone, computer, . . . Units / Definitions: Charge is measured in Coulombs, C. In practice the charge on an electron is 1.6 10-19C! Amperes: Defining charge in terms of the electron's charge would seem to be a good operational definition but for practical reasons the operational definition is in terms of current in Amperes, A, amps, I (Ampere was an early worker in electricity): 1Coulomb is defined as the charge carried by 1 Ampere in 1 second Generally for practical purposes people reverse this and consider 1A=1C/1second! The operational definition involves the force between current carrying wires and is only of interest to people at the National Bureau of Standards who must actually measure it! Everyday currents: A 100 watt light uses about 1A, ordinary extension chords can carry 10-15 A safely. River analogy: Charge is equivalent to amount of water (gallons, kg, and acre feet).