Which formula is used to find total resistance (Rt) in a parallel circuit?

In a parallel circuit, the total resistance is calculated using the formula that involves the reciprocals of the individual resistances. This approach reflects the nature of how current flows in parallel circuits; the current has multiple pathways to take.

When resistors are connected in parallel, the total effective resistance decreases because each additional resistor provides an alternative path for current to travel. Thus, combining the resistances requires using the reciprocal formula: the sum of the reciprocals of each individual resistance equals the reciprocal of the total resistance. Therefore, the statement 1/Rt = 1/R1 + 1/R2 + 1/R3 accurately describes how to calculate total resistance in parallel circuits.

The other formulas provided do not apply to parallel circuits. The formula which states Rt = R1 + R2 + R3 describes series circuits, where resistances add together directly. The expressions stating Rt as merely equal to the values of R1, R2, and R3, or as equal to R1, R2, and R3, do not reflect any standard formula for resistance in either configuration.