A long straight wire of length l( a) is made of two concentric conducting materials. The material of the inner tube for radius r ≤ a has a resistivity rho1. The material of the outer shell for radius a < r ≤ 2a has a resistivity rho2. The wire carries a total current I. (a) What is the total resistance R of the conducting wire.

R = rho/8api or

( rho2-rho1)/8pi

Explanation: you can substitute for rho = rh2 - rho1

Please find the attached file for the solution

answer: the exterior temperature of commercial jet planes as they leave the stratosphere and return to the ground increases steadily.

explanation:

the lower most layer of atmosphere is troposphere which extends from 0 to 12 km above the surface of the earth. the temperature initially decreases as distance is increased from the earth's surface. commercial jets fly in lower part of the stratosphere. the stratosphere extends upto 50 km. the temperature in stratosphere starts rising again due to presence of ozone which traps the uv rays.

thus, when the planes leave the stratosphere and return to the ground, the exterior temperature increases steadily.