What causes heat to be generated when current flows through a wire?

The generation of heat when current flows through a wire is primarily due to resistance in the wire itself. When an electric current passes through a conductor, like a copper wire, the movement of electrons encounters resistance, which is the opposition to the flow of electric current. This resistance causes energy to be transformed into heat, according to Joule's law, which states that the power of heat generated (in watts) is equal to the current squared multiplied by the resistance (P = I²R).

While voltage is necessary to drive the current through the conductor and energy is involved in the overall electric circuit, resistance is the key factor that directly results in heat production when current flows. Thus, understanding resistance is crucial for grasping why heat is generated in electrical conductors.