Electric cell: EMF and internal resistance
Electric current and circuits · Physics
Study notes
Example: A 9‑volt battery has an internal resistance of 1 Ω. It is connected to a 3‑Ω resistor (the load). Find the current flowing, the terminal voltage, and the power delivered to the load. Step 1: Let I be the current. Step 2: Use V = E – I·r. The terminal voltage V is also V = I·R (Ohm’s law for the load). Step 3: Set I·R = E – I·r. Step 4: Plug in values: I·3 = 9 – I·1. Step 5: Solve for I: 3I = 9 – I → 3I + I = 9 → 4I = 9 → I = 2.25 A. Step 6: Terminal voltage V = I·R = 2.25·3 = 6.75 V. Step 7: Power to load P = I²·R = (2.25)²·3 ≈ 15.19 W.