Ib Physics 5.2 «GENUINE»

Since energy ((E)) is power multiplied by time, the electrical work converted into heat over time (t) is (E = IVt).

[ P = I^2 R ]

The lost volts ((Ir)) are dissipated as heat inside the source. This explains why batteries become warm during heavy use and why a car battery’s voltage drops when starting the engine. The maximum power transfer theorem (often a HL extension) states that to extract maximum power from a source, the load resistance must equal the internal resistance, but this condition results in 50% efficiency—half the power is wasted as heat inside the source. The heating effect behaves differently under DC and AC. With DC, the current is constant, so the power dissipation is steady: (P = I^2R). With AC, the current varies sinusoidally. Since heating depends on (I^2), the average power is not zero (even though the average current over a cycle is zero). IB Physics introduces the root-mean-square (rms) values for AC: Ib Physics 5.2