An incandescent lightbulb contains a fi lament that has a certain electrical resistance R. The brightness of the bulb depends on the current and increases as the current through the fi lament is increased. Consider the following situations in Figure Q19.9. (a) Two identical lightbulbs are connected as shown to a single ideal battery as in circuit 2. Will the brightness of one of these bulbs be greater than, less than, or the same as the brightness of the bulb in circuit 1?
(b) Repeat part (a) for the bulbs in circuits 3, 4, and 5, comparing their brightness to that of the bulb in circuit 1. Explain your answers. 

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Lightbulb Circuit 3 Circuit 1 Circuit 2 Circuit 4 Circuit 5 Figure Q19.9 3.