Batteries are not just about magic energy! They have internal resistance which affects how they work in a circuit.

• Inside a real battery, there's an ideal cell (like a perfect battery) that has no resistance.
• There's also something called internal resistance, which does...well, resist.
• Both together = what's inside an actual battery.

• Internal resistance stays the same. (Reality Check - It can change because of various factors!)
• Emf (electromotive force) is steady. (Reality Check - It too can change!)

• Emf of the battery supplying energy = ε.
• The total potential differences (pds) in the circuit = IR + Ir.
• So, ε = I (R + r).
• If external resistor has a pd of V, then ε = V + Ir or V = ε – Ir.

✨ Real-World Connection: Think of it like filling up your car with gas. The gas pump (battery emf) gives energy. But not all of that energy goes into the car's engine (external circuit). Some is "lost" (like the gas that evaporates or spills) because of internal resistance.