Chapter 18 Direct-Current Circuits Quick Quizzes 1. (a), (d). Bulb R 1 becomes brighter. Connecting a wire from b to c provides a nearly zero resistance path from b to c and decreases the total resistance of the circuit from R 1 + R 2 to just R 1 . Ignoring internal resistance, the potential difference maintained by the battery is unchanged while the resistance of the circuit has decreased. The current passing through bulb R 1 increases, causing this bulb to glow brighter. Bulb R 2 goes out because essentially all of the current now passes through the wire connecting b and c and bypasses the filament of Bulb R 2 . 2. (b). When the switch is opened, resistors R 1 and R 2 are in series, so that the total circuit resistance is larger than when the switch was closed. As a result, the current decreases. 3. (a). When the switch is closed, resistors R 1 and R 2 are in parallel, so that the total circuit resistance is smaller than when the switch was open. As a result, the total current increases. 4.
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