In: Physics
4. Real batteries have an "internal resistance", so a real battery can modeled more or less realistically by an ideal battery in series with a resistor. Suppose the emf of the ideal battery is V and the internal resistance is r; if you connect this battery across a resistor R, find the "terminal voltage" across the battery, the current supplied, and the power dissipated in the battery. Compare this to the power dissipated by the battery if R = 0; in particular, take the ratio between the cases, and look at what happens when r is small. This is why short circuits are a bad idea; there's always a little bit of resistance in a real circuit.