Impedance (Z) combines resistance (R) and reactance (X) to show how much an electric circuit opposes current flow. All are measured in ohms (Ω). Reactance, caused by capacitors and inductors, acts like resistance but is imaginary. Inductors have inductive reactance (XL), capacitors have capacitive reactance (XC), and their formulas depend on frequency and component properties.Power (P) is the rate electrical energy does work, measured in watts (W). Since watts are small, we often use kilowatt-hours (kWh) for energy. 1 kWh = 1 unit of electricity = 1000 watt-hours = 3.6 million joules. 1 kW = 1000 watts, and 1 watt is the energy use of 1 joule per second.Crucially, energy (kWh) is the total electrical work done, while power (W) is the rate of doing that work. A Coulomb (C) measures electric charge, not energy. It describes the flow of charged particles like electrons.