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!

Homework Help: Zwiebach Exercise 9.3b

  1. Oct 5, 2007 #1
    1. The problem statement, all variables and given/known data
    Apparently the answer is sqrt(2 alpha') *4a. But doesn't equation 9.10 imply that the 4a should just be a 1?


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 5, 2007 #2
    It's kind of a coincidence that when I did that problem two years ago, that's what I wrote in the margin of my book. However it is not true. [itex]l_s[/itex] is just a unit of length like the Planck length. It is not necessarily the length of any string. It is useful as a unit of length when doing string theory as this problem shows. The answer is [itex]4\sqrt{2}a[/itex] in units of the string length.
     
    Last edited: Oct 5, 2007
  4. Oct 6, 2007 #3
    I see--we need to integrate differential lengths from sigma = 0 to sigma = 2 pi. Thanks.
     
    Last edited: Oct 6, 2007
  5. Oct 6, 2007 #4
    That's for closed strings. As this is an open string, the range is different.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook