How do you calculate the total resistance when resistors are in series?

• A. Multiply the resistances
• B. Take the reciprocal of the sum
• C. Use a formula Rt = (R1xR2)/(R1+R2)
• D. Add the resistances together

Answer: (D)

In a series circuit, the same current flows through every component, so the voltage across each adds up to the total voltage. If the supply voltage is V and the current is I, then the voltage drops are V1 = I·R1, V2 = I·R2, and so on. The total voltage is V = V1 + V2 + ... = I·(R1 + R2 + ...). Since the total resistance Rt is defined by V = I·Rt, it follows that Rt = R1 + R2 + ... For two resistors, Rt = R1 + R2. This additive behavior reflects how voltage redistributes across series elements while sharing the same current. The other forms correspond to different setups: multiplying would not match how voltage drops accumulate in series, the reciprocal of the sum is characteristic of parallel combinations, and (R1·R2)/(R1+R2) is the parallel formula for two resistors, not series.