Electricity and Magnetism: electric circuits (internal resistance and series-parallel networks) – Week 2 focus
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Subject: Physical Sciences
Class: Grade 12
Term: 2nd Term
Week: 2
Theme: General lesson support
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This week, we delve into the intricacies of electric circuits, specifically focusing on internal resistance and series-parallel networks. Understanding these concepts is crucial for anyone interacting with electricity, from using a cell phone to understanding how the national power grid functions. In South Africa, with our ongoing energy challenges and the need for efficient power usage, a solid grasp of circuit behavior is more important than ever. This knowledge can empower you to make informed decisions about energy consumption, understand alternative energy solutions, and potentially contribute to innovative solutions for our country's energy needs.
2.1 Internal Resistance Every real battery or cell possesses internal resistance (r). This internal resistance arises from the materials within the battery that impede the flow of charge. Think of it like the resistance you experience when trying to push a lot of people through a narrow doorway. The battery's internal resistance acts as a resistor inside the battery itself. The emf (electromotive force, ε) is the total energy provided per coulomb of charge by the battery.
However, because of the internal resistance, not all of this energy is available to the external circuit. Some of the energy is dissipated as heat inside the battery itself due to the internal resistance. The terminal potential difference (V terminal ) is the actual potential difference across the terminals of the battery when it is connected in a circuit and delivering current. It is always less than the emf due to the voltage drop across the internal resistance.
Formula: V terminal = ε - Ir Where: V terminal is the terminal potential difference (V) ε is the emf of the battery (V) I is the current flowing through the circuit (A) r is the internal resistance of the battery (Ω) This equation tells us that the terminal potential difference is equal to the emf minus the voltage drop across the internal resistance (Ir).