Ohm's Law and Resistance

Core concept

For resistors connected in series, total resistance is the sum of individual resistances (R = R₁ + R₂ + ...), and the same current flows through each; for resistors connected in parallel, the reciprocal of total resistance equals the sum of reciprocals of individual resistances (1/R = 1/R₁ + 1/R₂ + ...), with voltage being the same across each parallel branch. Materials like copper have low resistance (good conductors), while materials like rubber have very high resistance (insulators), and this property determines their appropriate electrical uses.