//example-18.4
//page no-547
//given
//resistance of wire
R=21  //ohm
//length of wire
l=200  //m
//diameter of wire
d=0.44*10^-3  //m
//area of cross section of wire
A=(%pi)/4*d^2  //m^2
//as we know that 
//R=rho*l/A
//so
rho=R*A/l  //ohm m
printf ("the specific resistance of wire is %e ohm m",rho)