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Homework Help: Light Bulbs in a parallel circuit

  1. Jan 25, 2006 #1
    Q: Two bulbs x and y are connected in parallel to a new dry cell. The switch is closed. If bulb x is unscrewed, the brightness of bulb y will
    a) double
    b) halve
    c) remain the same
    d) become 0

    A: a? The current from the first branch would go into the second branch?
  2. jcsd
  3. Jan 26, 2006 #2


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    Staff Emeritus
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    The voltage remains the same. What happens when bulb is removed? Think about the resistance of each bulb, and the relationship between voltage, current and resistance.
  4. Jan 26, 2006 #3


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    Staff: Mentor

    It depends on the battery chemistry. But as with many subtle multiple-choice questions, there is only one best answer in the choices given (as Astro has indicated).

    In the real world, however, batteries have a finite output impedance, so even a new battery's output voltage will droop some as it is loaded more. So the output voltage will be a bit less when it is outputting twice the current (to drive both bulbs). So if there were an answer e) that said "increase slightly", that would be the correct choice. Since that isn't listed, what is the next best choice?
  5. Jan 26, 2006 #4


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    Science Advisor
    Gold Member

    The light bulbs in your home are wired in parallel. If you unscrew one, how does it affect the others?
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