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Simple Circuit diagram Question

  1. Sep 14, 2011 #1
    The diagram shows identical lamps X and Y connected in series with a battery. The lamps light with normal brightness. A third lamp Z is connected in parallel with lamp X.

    What happens to the brightness of lamp Y?
    A) Brighter than normal
    B) Normal
    C) Dimmer than normal
    D) Very dim (cannot be seen)


    I'm completely clueless about it and slightly confused. Any help would be appreciated.
     
  2. jcsd
  3. Sep 14, 2011 #2
    Think of it in terms of resistors - is there a difference in total resistance between the first situation and the second?
     
  4. Sep 14, 2011 #3

    Doc Al

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    Staff: Mentor

    What do you think happens? Hint: See if you can figure out how the current passing through lamp Y changes (if it does).
     
  5. Sep 14, 2011 #4
    Hmms, I would have to say, yes?
     
  6. Sep 14, 2011 #5
    Hmm, wouldn't the additional lamp added in parallel alter the current in the entire circuit?
     
  7. Sep 14, 2011 #6

    Doc Al

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    Yes, so what happens to the current going through lamp Y? Increase, decrease, or remain the same?
     
  8. Sep 14, 2011 #7
    I'm not so sure, but I would say increase.
     
  9. Sep 14, 2011 #8

    Doc Al

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    Guessing doesn't count.

    Take daveb's hint: The lamps are like resistors. What happens to the total resistance and thus to the current?
     
  10. Sep 14, 2011 #9
    Total resistance decreases, current increases.
     
  11. Sep 14, 2011 #10

    Doc Al

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    Good!
     
  12. Sep 15, 2011 #11
    Oh so the bulb is brighter?
    Thanks for helping guys!
     
  13. Sep 15, 2011 #12

    Doc Al

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    Staff: Mentor

    Right.

    Adding that resistor in parallel with X drops the total resistance, which increases the current flowing through Y. More current means a brighter bulb.
     
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