A coaxial cable has an inner, solid wire of radius and outer, hollow wire of radius . A current flows through the inner wire and returns through the outer wire. Assuming that the cable is vey long calculate the magnetic field energy per unit length.

Which of the following best describes internal energy? a. the difference between the kinetic and potential energies of the particles in a system b. the sum of the kinetic and potential energies of the particles in a system c. the sum of the kinetic and thermal energies of the particles in a system d. the difference between the kinetic and thermal energies of the particles in a system