EMF & Internal Resistance

Real cells have internal resistance.

Concept

EMF & Internal Resistance is a foundational idea in this chapter. The defining relationship is:

$V = \varepsilon - Ir$

Terminal voltage drops under load; equals EMF at I=0 (open circuit).

Worked Application

Apply the formula to a typical problem from your textbook. Identify the knowns, plug into the equation, and check that the units work out. Always sanity-check the magnitude before accepting an answer.

Common Confusions

• Confusing the variables in the formula — re-read the symbol definitions in the chapter.
• Forgetting unit conversions (cm vs m, g vs kg).
• Ignoring sign conventions where direction matters.

Key Takeaways

• Master the formula $V = \varepsilon - Ir$ and one canonical example.
• See the chapter index for full derivations, traps and exam-grade problems.