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Light bulb brightness (series and parallel)

  1. Feb 26, 2006 #1
    Hi, my question relates to light bulb brightness in a circuit with light bulbs connected in series and in parallel. Ill give you the question and then my argument.


    Q1:In this diagram light bulbs A,B, and C are all equal. Rank in order the most bright to the least bright.
    A1: I would argue that B and C are equal in brightness and are both greater in brightness than A because the amount of current running through B and C is equal and greater than A, and since the amount of current running through a bulb determines brightness, A must be the least bright.

    Q2: Suppose a wire is connected between points 1 and 2 running through bulb C. What happens to the brightness in all the bulbs
    A2: Bulb C would be short circuited and thus go out, but I am not sure what happens to A and B. Please help

    Q3: What happens to the current drawn from the battery when the wire is connected
    A3: The current drawn from the battery is decreased because there is no current flowing through C?? Please help

    Sorry for the long post but please look over my arguments and tell me if im right or wrong. THANKS!!
  2. jcsd
  3. Feb 27, 2006 #2
    For A1, I'm not too sure about the second part, but anyway, this is what I think: I agree that B & C will be equal brightness, but disagree with them being brighter than A. Surely A would be brighter since there is a separation of the circuit, the current will be split (I don't know if you know about Kirchoff's Laws), and so the current will be less through B&C, and so will be less bright. I think that's right.

    For A2, yes, C will go out, but I think that B will get dimmer (possibly go out aswell), and A will get brighter.

    For A3, I think that the current drawn will increase, since there is less resistance, but again, I'm not entirely sure.
  4. Feb 27, 2006 #3


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    Read Finchie_88's post, s/he is correct.
  5. Feb 27, 2006 #4
    thank you very much for your help
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