Haitham Khouri

DC  means direct current. it has a constant direction intensity of current can vary with time but the direction of movement stays the same at all times this type of sources are produced by solar cells, batteries and thermocouples etc DC power is widely used in low voltage applications such as charging batteries, automobiles etc. alternating current (AC) is an electric current which periodically reverse direction in contrast to direct current which flows only in one direction alternating current magnitude changes with time

Electric power system is a network of electrical components used to supply, transmit and use electric power. An example of an electric power system is the network that supplies a region's home and industry with power for sizable regions, this power system is called the grid and can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating stations to the load centers and the distribution system that feeds the power to nearby homes and industries. Small power systems are also found in industry, hospitals, homes and commercial buildings. The majority of these systems relay upon "three-phase AC power' the standard for large scale power transmission and distribution across the modern world. Specialized power systems that do not rely upon the three-phase AC power are found in aircraft, electric rail systems, automobiles etc.

So there are two ways to measure resistor. 1) Using multimeter In which You connect probe to both end of resistor and switch the knob of multimeter to indicated resistance value. 2) Using colour coding Let suppose  A resistor colored  Yellow-Violet-Orange-Gold  would be 47 * 10^3 Ω with a tolerance of +/- 5%. example (2) A resistor colored  Green-Red-Gold-Silver  would be 52 * 10^-1 Ω with a tolerance of +/- 10%.