Demos: 5B-04 Voltage Drops Equal EMF

The circuit shown is used to demonstrate that the sum of the iR drops equals the EMF of the battery, as required by Kirchoff’s Rule.

Directions: First place the voltmeter across the battery terminals to show the EMF. Then close the switch and measure the potential difference across each resistor. Since the current is the same in each resistor, the iR drops are proportional to the resistances.

Suggestions for Presentation: This is fairly straightforward. Be sure the students understand that the current is the same in each resistor. You might want to suggest a way of looking at this without doing a straight iR calculation. The total resistance is 60W, so the proportions of the total resistance are 1/6, 1/3 and 1/2, respectively. Then the voltage drops should be 1/2 V, 1 V and 1.5 V, respectively.

Applications: Voltage divider circuits.

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