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Homework Help: Really basic what happens when the switch closed question

  1. Apr 19, 2008 #1
    Hello guys,

    I got a small question. It says circuit consists of three identical lamps connected to a battery with a switch as shown in the diagram. When the switch is closed what happens.

    I did this really quick on paint.


    they are not allowing me to post URL because I don't have 15 posts. I'll do some spaces and stuff please type the w w w thing properly.

    It says that lamps C turns off because no current flows through it. But I don't get it. Shouldn't the current divide and each section get some current. Why is C getting no current when the switch is closed. Any help would be appreciated. Thanks:rolleyes:smile:
    Last edited by a moderator: Apr 29, 2008
  2. jcsd
  3. Apr 19, 2008 #2
    You are supposed to have both positive and negative current for the lamp to turn on, no?
  4. Apr 19, 2008 #3


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    The switch and wire in parallel with the "C" lamp have extremely low resistance.
    The "C" lamp will have much higher resistance in comparison.
    When the switch is closed, nearly all of the current will flow through the switch.
    The current flowing through the lamp will not be sufficient to cause it to illuminate.

    For theoretical schoolwork problems, the resistance in the switch and wires are generally assumed to be zero. So when the switch is closed, there will be no voltage drop across the "switch" leg of the circuit. With no voltage drop across the "C" lamp, there will be no current.
  5. Apr 20, 2008 #4
    Thank you for your help:smile:. I think I get it now. The current took the path of least resistance in this circuit. Let's say there was a resistor in the wire with the switch then you would see more current flow to the globe. Am I right!!. Thanks a lot for the help. Really appreciate it. :smile:
  6. Apr 20, 2008 #5


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    Exactly right.
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