what is resistance

Resistance is a measure of the opposition to current flow in an electrical circuit. It is a force that counteracts the flow of electricity and influences the flow of electricity. Resistance values are expressed in ohms (Ω), and the standard unit of resistance is the ohm. The greater the resistance, the lower the current, and the lower the resistance, the greater the current. All materials resist current flow to some degree, but they fall into one of two broad categories: conductors and insulators. Conductors are materials that offer very little resistance where electrons can move easily, while insulators are materials that offer high resistance to the flow of electrons. The resistance of an object is defined as the ratio of voltage V across it to current I through it, while the conductance G is the reciprocal. Resistance depends on the size and shape of an object because these properties are extensive rather than intensive. For example, a wires resistance is higher if it is long and thin, and lower if it is short and thick. Many components, such as heating elements and resistors, have a fixed-resistance value, and these values are often printed on the components nameplates or in manuals for reference.