1. Limited time only! Sign up for a free 30min personal 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!

Ranking brightness of lightbulbs in a circuit

  1. Mar 4, 2017 #1
    1. The problem statement, all variables and given/known data

    In the circuit shown, all the light bulbs are the same. Why is the following statement true? :

    A is the brightest. B and C are equally bright, but are dimmer than A.


    https://pbs.twimg.com/media/C6GllsQVMAA4chz.jpg:large [Broken]
    https://twitter.com/FauxNews101/status/838133087464640513 [Broken]

    2. Relevant equations

    P = I * V

    3. The attempt at a solution

    There is more of a voltage drop across B to C than A, so the power is less for both B and C than A since power is proportional to I and V? Since B and C are the same then they should be the same brightness because they each have the same resistance, in series?
     
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Mar 4, 2017 #2

    berkeman

    User Avatar

    Staff: Mentor

    No. lightbulb A is in parallel with B+C. So the voltage drop across B is half of that across A, and the drop across C is half that across A.

    Try again? :smile:
     
  4. Mar 4, 2017 #3
    The voltage drop of B+C equals the voltage drop of A. This is so because light bulb A equals the voltage drop across the equivalent of B+C since light bulbs in parallel have the same voltage. So B or C has half the voltage that A does; and because of that, the power for B and C is equal, but B or C is less power than A.
     
  5. Mar 4, 2017 #4

    berkeman

    User Avatar

    Staff: Mentor

    Yes, good. :smile:
     
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: Ranking brightness of lightbulbs in a circuit
Loading...