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!

Solving Umax with Pmax and Ohms

  1. Aug 20, 2013 #1
    Brief personal intro, I have last time studied physics about 12 years ago.

    I am now starting in 2 weeks time in a university and there is mandatory physics course so I am trying to relearn and learn as much as I can before that time.

    For that reason I am trying to solve text book tasks from my old physics books.

    I have never been good at maths nor physics atleast not calculations. Thus I appreciate thorough-Step by Step explanations so I can understand the solution.

    Thank you for your time


    1. The problem statement, all variables and given/known data

    How large voltage U , can be attached to the circuit , when both the resistance have an Pmax of 0,25 W ?

    R1 = 120Ω
    R2=180Ω

    They are in series.

    Answer is :
    Umax = 11

    2. Relevant equations

    P = U * I
    U = R * I


    3. The attempt at a solution


    0,25*120= 0,002083333333
    0,25*180= 0,003888888889

    0,002083333333 + 0,003888888889=0,00347222222

    0,00347222222*120 = 0,416666664
    0,00347222222*180 = 0,624999996

    4,16666664+6,24999996= 10,41666666
     
  2. jcsd
  3. Aug 20, 2013 #2
    Since they're in series, they have the same current through them. If you start with a low current and slowly ramp it up, do you know which of the resistors will reach its thermal limit first?
     
  4. Aug 21, 2013 #3
    No , it is not mentioned on the task nor which direction the current will go
     
  5. Aug 21, 2013 #4
    Just assume that you can control the current through the resistors, I promise you that I'll get to the point shortly :smile:

    Say you have a current of 1 A through the resistors. How much power is then dissipated in each resistor?
     
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: Solving Umax with Pmax and Ohms
  1. Resistance, ohms (Replies: 5)

  2. Ohm's Law (Replies: 4)

  3. Ohms law (Replies: 1)

  4. Ohm's law (Replies: 3)

  5. Genarilsed ohm (Replies: 3)

Loading...