Lesson Plan

• Describe the definition of electromotive force (e.m.f.) and how it differs from potential difference.
• Explain why e.m.f. is measured in volts and relate 1 V to 1 J / C.
• Apply the concept of e.m.f. to determine the open‑circuit voltage of common sources using a voltmeter.
• Analyse the effect of internal resistance on the terminal voltage when a circuit is closed.

• Voltmeters or digital multimeters
• AA alkaline cells, 9 V battery, and a mock car battery
• Simple circuit boards with a load resistor
• Projector and slide showing the e.m.f. diagram
• Worksheet with comparison table and short questions
• Whiteboard and markers

Begin with a quick demonstration: connect a voltmeter across an AA cell and ask, “What are we actually measuring?” Review students’ prior knowledge of voltage as “electric pressure.” State that today they will be able to identify e.m.f. as the maximum voltage a source can provide and will know how to measure it in volts.

1. Do‑now (5'): Students complete a short quiz on voltage symbols and units.
2. Mini‑lecture (10'): Define e.m.f., contrast with potential difference, and show the 1 V = 1 J/C relationship.
3. Demonstration (8'): Measure e.m.f. of an AA cell and a 9 V battery with the circuit open; record values.
4. Guided practice (12'): In pairs, students use multimeters to measure e.m.f. of provided sources, fill the worksheet table, and discuss internal‑resistance effects.
5. Concept check (5'): Quick “thumbs up/down” questions on common misconceptions.
6. Summary discussion (5'): Reinforce key points and answer lingering questions.

Recap that e.m.f. is the open‑circuit voltage measured in volts and that internal resistance causes a drop when current flows. Ask students to write one sentence on an exit ticket describing how to measure e.m.f. Assign homework to research the e.m.f. values of three household devices and bring the findings to the next class.