Electrical resistance is a fundamental physical property quantifying the opposition to the flow of electric current within a material. It is measured in ohms and arises because the free charges traveling through a conductor encounter collisions with the material's atoms, which dissipates energy as heat. The magnitude of resistance is determined by the material's inherent resistivity, the physical length of the conductor, and its cross-sectional area. Conductance is defined as the reciprocal of resistance, representing the ease with which electric current passes through a substance, and is measured in siemens. Materials exhibiting high conductance are excellent conductors, while materials with high resistance are insulators.