Activity 01
Pairs Experiment: Internal Resistance Measurement
Pairs connect a battery, high-resistance voltmeter, and variable load resistor in series. They record terminal PD for currents from 0 to 0.5 A using an ammeter. Students plot V against I; the gradient gives -r and y-intercept gives EMF. Discuss sources of error.
Explain how internal resistance affects the power delivered by a real battery.
Facilitation TipDuring the Pairs Experiment, remind students to record both open-circuit and loaded voltages immediately so they can compare the drop directly on the same worksheet.
What to look forPresent students with a circuit diagram showing a battery with EMF E and internal resistance r, connected to an external resistor R. Ask them to write down the equation for the terminal potential difference and the current flowing in the circuit. Then, ask them to calculate the terminal voltage if E = 6.0 V, r = 0.5 Ω, and R = 5.0 Ω.
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Activity 02
Small Groups: Power Delivery Circuits
Groups assemble circuits with a battery and three load resistors. They measure current, terminal PD, and calculate power for each load. Compare power outputs to identify maximum power point. Groups present findings on how internal resistance limits efficiency.
Analyze the factors that cause a battery's terminal voltage to drop under load.
Facilitation TipWhen running the Small Groups Power Delivery Circuits, circulate with a multimeter to verify resistor values before students close switches and risk overheating components.
What to look forPose the question: 'Imagine you have two identical batteries, but one has a significantly higher internal resistance. How would this difference affect the power delivered to a small motor connected to each battery, and why?' Facilitate a class discussion focusing on the concepts of voltage drop and power efficiency.
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Activity 03
Whole Class Demo: Open vs Load Voltage
Demonstrate open-circuit voltage with voltmeter only, then add loads to show drop. Class predicts and records values on shared whiteboard. Follow with paired predictions for a new battery using prior data.
Design an experiment to determine the internal resistance of a power source.
Facilitation TipFor the Whole Class Demo, measure the open-circuit voltage first, then connect the load while students watch the meter so they witness the drop in real time.
What to look forProvide students with a graph plotting terminal voltage against current for a real cell. Ask them to identify the EMF and the internal resistance from the graph. Then, ask them to predict the terminal voltage if the current were doubled.
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Activity 04
Individual Graph Analysis: V-I Plots
Provide printed V-I data sets from different batteries. Students graph manually, determine E and r, then compare ideal vs real sources. Extend to calculate maximum power.
Explain how internal resistance affects the power delivered by a real battery.
Facilitation TipIn the Graph Analysis activity, ask students to sketch predicted curves before plotting, forcing them to confront any lingering confusion between EMF and terminal voltage.
What to look forPresent students with a circuit diagram showing a battery with EMF E and internal resistance r, connected to an external resistor R. Ask them to write down the equation for the terminal potential difference and the current flowing in the circuit. Then, ask them to calculate the terminal voltage if E = 6.0 V, r = 0.5 Ω, and R = 5.0 Ω.
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Generate Complete Lesson→A few notes on teaching this unit
Teachers should anchor this topic in hands-on measurement rather than derivation, because research shows students grasp internal resistance best when they feel the voltage sag under their own fingers. Avoid launching straight into V = E – Ir; instead, let the data suggest the equation. Use whole-class whiteboard space to pool class results so patterns emerge collectively, and reserve the equation for the moment students ask, “Why does it slope like that?”
Successful learning looks like students confidently distinguishing EMF from terminal voltage and explaining why all real cells show a downward-sloping V–I graph. They should be able to calculate internal resistance from experimental data and justify why maximum power occurs at a specific current rather than at maximum current.
Watch Out for These Misconceptions
During Whole Class Demo: Open vs Load Voltage, watch for students who think the terminal voltage never changes once the battery is made.
Use the demo’s open-circuit reading as EMF, then show the immediate drop when the load closes; ask students to record both voltages on the same whiteboard and label the difference r·I.
During Pairs Experiment: Internal Resistance Measurement, watch for students who assume only weak or old batteries have internal resistance.
Have pairs test both fresh and gently used AA cells; guide them to calculate r for each and compare class data to see that all real cells behave similarly under load.
During Small Groups: Power Delivery Circuits, watch for students who believe increasing current always increases power output.
Ask groups to plot power against current using their measured terminal voltages; when the curve peaks, prompt them to derive I = E/(2r) from P = E·I – I²·r.
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