Lesson Plan

• Describe the concept of electromotive force (e.m.f.) as the energy transferred per coulomb of charge by a source.
• Explain the relationship V = 𝓔 – Ir and how internal resistance affects terminal voltage.
• Apply the V‑I graph method to determine a source’s e.m.f. and internal resistance from experimental data.
• Analyse common sources of error in e.m.f. measurements and suggest mitigation strategies.

• Projector or interactive whiteboard
• Lab bench with power supply (battery) and variable resistor
• Ammeter and voltmeter (analog or digital)
• Connecting wires and alligator clips
• Graph paper or spreadsheet software
• Worksheet with data‑table template
• Safety goggles

Today we’ll explore how a battery actually “pushes” charge around a circuit. Recall that voltage represents energy per charge and that Ohm’s law links V, I and R. By the end of the lesson you will be able to define e.m.f., calculate it from terminal voltage and internal resistance, and use a V‑I plot to find these values.

1. Do‑now (5') – Quick quiz on voltage, current and resistance definitions.
2. Mini‑lecture (10') – Introduce e.m.f., internal resistance, and the equation V = 𝓔 – Ir.
3. Demonstration (10') – Set up a simple circuit; show real‑time readings on ammeter and voltmeter.
4. Guided lab activity (20') – Students vary external resistance, record I and V for three settings, and plot V against I.
5. Data analysis (10') – Calculate gradient (‑r) and V‑intercept (𝓔); discuss error sources.
6. Check for understanding (5') – Concept questions and an exit‑ticket prompt.

We reviewed how e.m.f. quantifies the energy a source supplies per coulomb and how internal resistance reduces the terminal voltage. Students now complete an exit ticket summarising the calculation steps and receive a worksheet with a new data set for homework.