What is the formula for total resistance (RT) in a series circuit?

In a series circuit, the total resistance (RT) is calculated by simply adding together the individual resistances of all components connected in the circuit. This is because, in a series configuration, the current that flows through the circuit is the same for each resistor, and the total voltage across the circuit is the sum of the voltages across each resistor. Therefore, the formula for total resistance is RT = R1 + R2 + R3, where R1, R2, and R3 are the resistances of each component in the circuit.

This addition reflects the cumulative effect of each resistor on the overall resistance faced by the current flowing through the circuit. Each additional resistor increases the total resistance, which reduces the overall current flow for a given voltage according to Ohm's Law (V = IR).

The other options represent incorrect concepts: the second option pertains to parallel resistance calculations, the third suggests a multiplication which does not correctly apply to resistors in series, and the fourth indicates subtraction, which is not relevant in this context.