Impedance Z is the vector sum of which two quantities?

• A. Resistance and current
• B. Resistance and reactance
• C. Voltage and current
• D. Capacitance and inductance

Answer: (B)

Impedance is the combination of resistance and reactance in AC circuits treated as a vector. The real part, resistance, accounts for energy that is dissipated as heat, while the imaginary part, reactance, accounts for energy temporarily stored in electric and magnetic fields. In phasor form, impedance is Z = R + jX, so its magnitude is |Z| = sqrt(R^2 + X^2) and its angle is θ = atan(X/R). This is why impedance is described as the vector sum of resistance and reactance. Voltage and current are related by V = IZ, but they are the quantities connected by impedance rather than the components that make up impedance. Capacitance and inductance influence reactance, but they are not the direct components that sum to impedance.