일반물리학 2 — Gauss' Law: Problem 27

27 Two long, charged, thin-walled, concentric cylindrical shells have radii of 3.0 and 6.0 cm. The charge per unit length is \(-7.0 \times 10^{-6} \text{ C/m}\) on the inner shell and \(+5.0 \times 10^{-6} \text{ C/m}\) on the outer shell. What are the (a) magnitude \(E\) and (b) direction (radially inward or outward) of the electric field at radial distance \(r = 4.0 \text{ cm}\)? What are (c) \(E\) and (d) the direction at \(r = 8.0 \text{ cm}\)?