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!

Entropy - physical system

  1. Jan 29, 2007 #1
    1. The problem statement, all variables and given/known data
    A 50 ohm resistor carries a current of 250 mA and is maintained at a constant temperature of 303K by thermal contact with a heat sink.

    Calculate the entopy change of

    i) the resistor, and
    ii) the universe,

    if the current flows for 30 seconds.


    2. Relevant equations
    dS >= 0?


    3. The attempt at a solution
    I'm not sure how to attempt this question for a physical problem. Up until now I've been restricted to doing questions of this type based upon ideal gases, so I'm not sure how I would apply that to a physical system like this. Any hints anyone?
     
  2. jcsd
  3. Jan 29, 2007 #2
    Right, I've had another look at this.

    I've said that dQ=dW and that work = power * time, so dW = Pdt = I*I*R*dt

    From here I've substituted this into the equation [tex]dS = \int \frac{I^2R}{T}dt[/tex] with limits 0 and 3.

    Following this through I get an answer of 0.031 J/kg. Does this sound about right? Then for the entropy change of the universe it'll be just the negative of this answer?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Entropy - physical system
  1. Entropy of a system (Replies: 4)

Loading...