1. The problem statement, all variables and given/known data A laboratory lead consists of 16 strands of fine copper wire twisted together. Each strand is 30 cm long with a diameter of 0.15 mm. Calculate the potential difference across the lead when it is carrying a current of 2.0 A. (The resistivity of copper = 1.7 × 10^-8 Ohm*m) 2. Relevant equations What I would do is R = pl/A and then multiply by 2 BUT I can't find R 3. The attempt at a solution (the answer is. apparantly, 0.036 V but I cant see how) I said R = [(1.7*10^-8)*16*0.3)/(pi*0.15/20000)^2)
Putting strands of wire in parallel decreases the total resistance, because the electrons now have many more paths to follow. 16 strands would decrease the resistance by a factor of 16. Also, why are you dividing 0.15 by 20,000? Why is pi being squared? The area of a circle of pi*r^2, not (pi*r)^2.
er, sorry abou the pi^2 bad use of brackets it was meant to be pi * (0.15/2000)^2 again sorry, Question: it is still ONE strand of wire, just twisted, are you sure total R decreases
http://www.edexcel.com/migrationdocuments/QP GCE Curriculum 2000/June 2009/6PH02_01_que_20090521.pdf BUT if you look at page 19 then we multiply by 8 not divide by 8 why??
oh, don't worry I get it first example 16 seperate strands second example one strand with 8 branches its ok