What is the formula for impedance?

What is the formula for impedance?

• A. Impedance = Current / Electromotive force
• B. Impedance = Electromotive force * Current
• C. Impedance = Electromotive force / Current
• D. Impedance = Electromotive force - Current

Answer: (C)

Impedance is the opposition a circuit offers to alternating current, measured by how much voltage is needed to push a certain current. Since electromotive force is another term for voltage, impedance is the voltage divided by the current: Z = V / I. That means the unit is ohms (volts per ampere). The other expressions don’t describe impedance: current divided by voltage would give conductance, voltage times current gives power, and subtracting voltage and current isn’t a meaningful electrical quantity in this context.

Impedance is the opposition a circuit offers to alternating current, measured by how much voltage is needed to push a certain current. Since electromotive force is another term for voltage, impedance is the voltage divided by the current: Z = V / I.

That means the unit is ohms (volts per ampere). The other expressions don’t describe impedance: current divided by voltage would give conductance, voltage times current gives power, and subtracting voltage and current isn’t a meaningful electrical quantity in this context.