When studying electric circuits, you may come across the term voltage source. A voltage source supplies voltage to a circuit. However, ideal and real voltage sources behave differently when a load is connected. For example, an ideal voltage source maintains a constant output voltage even when the load resistance \(R\) changes. A real voltage source has internal resistance, so its output voltage decreases as the load current increases. This article uses diagrams to explain the following topics: What a voltage source is Voltage across the load when the source’s internal resistance \(r\) is zero Voltage across the load when the ...