For two impedances Z1 and Z2, what are the series and parallel formulas for total impedance?

• A. Series: Z1 Z2; Parallel: 1/(Z1 Z2)
• B. Series: Z1 + Z2; Parallel: 1/Z1 + 1/Z2
• C. Series: Z1 - Z2; Parallel: Z1 Z2
• D. Series: Z1 + Z2; Parallel: Z1 Z2 / (Z1 + Z2)

Answer: (B)

Impedances combine differently depending on how they’re connected. In series, impedances simply add: the total Z is Z1 plus Z2. In parallel, the currents add, so the total impedance comes from the reciprocal sum: 1/Z_total = 1/Z1 + 1/Z2. That can be written as Z_total = 1/(1/Z1 + 1/Z2) or, equivalently, Z_total = (Z1 Z2)/(Z1 + Z2).

So the correct form uses series as Z1 + Z2 and parallel as Z1 Z2 divided by (Z1 + Z2). A form that writes the parallel result as 1/Z1 + 1/Z2 would be giving the total admittance, not the impedance.