Question 83016
The electrical resistance (R) of a wire varies directly as its length(L) and inversely as the square of its diameter (d). A wire 20 meters long and 0.6 centimeters in diameter made from a certain alloy has a resistance of 36 ohms.  What is the resistance of a piece of wire 60 meters long and 1.2 centimeters in diameter made from the same material?  The answer is multiple choice.
a. 24 ohms
{{{highlight(b)}}}. 27 ohms
c. 30 ohms
d. 48 ohms
Directly means multiply, inversely means divide, k is the constant of proportionality. 
{{{R=kL/(d^2)}}} when L=20 and d=.6, R=36, find k
{{{36=k(20)/((.6)^2)}}}
{{{36=20k/.36}}}
{{{(.36/20)*36=(.36/20)*(20k/.36)}}}
{{{.648=k}}}
Therefore the formula is: {{{R=.648L/(d^2)}}}, let L=60 and d=1.2 and solve for R.
{{{R=.648(60)/(1.2^2)}}}
R=27 ohms
Happy Calculating!!!!