1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Kirchoff's Law - Wire in parallel with light bulb

  1. May 31, 2015 #1
    1. The problem statement, all variables and given/known data
    If you measure the resistance of the three lightbulbs (independently) and get the following values. What is the equivalent total resistance of the circuit, and it’s uncertainty.
    [tex] R_1 = (50 \pm 7) \Omega, \ \ R_2 = (720 \pm 30) \Omega, \ \ R_3 = 140 \pm 20) \Omega [/tex]
    upload_2015-5-31_2-34-15.png
    Now you connect a bare wire (with negligible internal resistance) between to the left and right of L2 respectively in the circuit diagram. What will happen to the brightness of each bulb (i.e. will it increase, decrease, or remain the same)? Justify your results by finding the power of each light bulb in terms of ∆Vbat.

    2. Relevant equations
    [tex] \frac{1}{R_{eq}} = \frac{1}{R_{L2}} + \frac{1}{0} [/tex]

    3. The attempt at a solution
    [tex] \frac{1}{R_{eq}} = \frac{1}{720 \ \Omega} + \frac{1}{0} [/tex]
    [tex] R_{eq} = 0 \Omega [/tex]

    Knowing that the resistance in the top half of the parallel component of this circuit is now 0, does that imply that the current, I1, into the parallel component is now equivalent to I2, the current into L2 and the wire? I.E. is there any power going through L3 after the wire is connected?

    Thank you in advance!
     
  2. jcsd
  3. May 31, 2015 #2

    Svein

    User Avatar
    Science Advisor

    Well, what do you think? What is the voltage across L2 (and L3)?
     
  4. May 31, 2015 #3
    I think that all (minus a negligible amount) the current will flow through the wire, making the Voltage drop across L2 and L3 zero.
     
  5. May 31, 2015 #4

    Svein

    User Avatar
    Science Advisor

    Yes. Therefore, the voltage across L1 is...
     
  6. May 31, 2015 #5
    It should be equal to the voltage of the battery. Thanks for your help.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Kirchoff's Law - Wire in parallel with light bulb
  1. Light Bulb in Ohm Law (Replies: 4)

Loading...