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Illustration 30.2: Switches, Voltages, and Complete Circuits


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This Illustration allows you to control the current flow through a circuit using switches (voltage is given in volts). Restart.

You can open and close switches to turn the lightbulbs on and off. (How is this similar to a bulb breaking in Illustration 30.1?) Notice that when bulb 1 is dark (S1 open and the other switches closed), there is no complete path for the current, so none of the bulbs light. Furthermore, there must be 0 V across bulbs 2 and 3, and there is 10 V across the switch S1. Similarly, when bulb 2 is dark (S2 open and the other switches closed), there is a complete path for current flow through bulbs 1 and 3 (and the voltage across each is 5 V). The same reasoning applies to bulb 3 when switch 3 is open. (When all the switches are open, the voltmeter readings can have any value, as long as the sum adds up to 10 V.)

Illustration authored by Anne J. Cox.

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