Introduction
 

Every cell or battery has an electromotive force (emf), which represents the energy supplied to each coulomb of charge. In real electrical circuits, some of this energy is dissipated inside the cell itself due to its internal resistance, meaning the terminal potential difference is often less than the emf when current is flowing.
 

In this topic, students learn the difference between emf and terminal potential difference, investigate the effects of internal resistance, and apply these concepts to analyse practical electrical circuits.
 

AQA A Level Physics Specification: 3.2.4.4 EMF and Internal Resistance
 

What You Need to Know
 

• Define electromotive force (emf) as the energy supplied per unit charge.

• Understand that emf is measured in volts (V).

• Distinguish between emf and terminal potential difference.

• Define internal resistance and explain its effect on circuit performance.

• Understand why the terminal potential difference decreases as current increases.

• Apply the relationship between emf, terminal potential difference, current and internal resistance.

• Calculate energy transferred and power dissipated within a cell.

• Interpret current–terminal potential difference graphs.

• Explain the concept of lost volts and their relationship to internal resistance.
   

Downloadable Topic Pack
 

EMF and Internal Resistance Topic Pack Exam Questions and Answers
 

Related Topics
 

• Energy & Power

• Potential Divider

• IV Characteristics and Electricity Basics

• Resistivity & Superconductors

• Electric Potential