7. Find the resistance between inner and outer conductors of a coaxial cable (shown in Fig. 5) with the following parameters: \( a = 0.500 \, \text{cm} \), \( b = 1.75 \, \text{cm} \), \( L = 30.0 \, \text{cm} \), and \( \rho = 1.0 \times 10^{13} \, \Omega \cdot \text{m} \) (resistivity of polyethylene (聚乙烯)) (以科學記號表示且四捨五入至小數點3位) (10 points)