resistansen

Resistansen is the electrical property of a material or component that opposes the flow of electric current. It is defined as the ratio of the voltage across the element to the current through it, expressed by Ohm’s law as R = V / I. The unit of resistance is the ohm, symbolized by the Greek letter omega (Ω). A device that follows Ohm’s law over a range of voltages and currents is called a linear resistor; real devices may show non-ideal behavior at extremes.

Resistansen depends on material, geometry and temperature. For a homogeneous conductor, R = ρ L / A, where ρ is resistivity, L is length and A is cross-sectional area. Materials with high resistivity, such as rubber, have high resistance, while metals with low resistivity have low resistance. The temperature coefficient α describes how R changes with temperature: ΔR ≈ R0 α ΔT. In practice, resistance generally increases with temperature for most metals.

In circuits, resistances add in series and combine in parallel according to standard rules: R_series = sum R_i, 1/R_parallel = sum 1/R_i. In alternating current, impedance generalizes resistance to include reactance; a pure resistor has resistance that is essentially constant with frequency.

Measurement and applications: resistance is measured with an ohmmeter or bridge. Resistors are fundamental circuit components, used for current limiting, voltage division, biasing, and heating elements. The concept connects to related ideas such as resistivity, impedance, and temperature dependence.