10.2.6—The formula for the combined resistance of two or more resistors in parallel

For parallel resistors, each branch has the same potential difference and currents add, giving 1/R_total=Σ(1/R_i).

Use reciprocal values carefully and check that the equivalent resistance is below the smallest branch resistance.

Two 6 Ω resistors in parallel give 1/R=1/6+1/6, so R_total=3 Ω.

Parallel branches do not carry equal current unless their resistances are equal; they share voltage, not necessarily current.