(Solved): 37. A loose spiral spring carrying no current is hung from a ceiling. When a switch is thrown so t ...

37. A loose spiral spring carrying no current is hung from a ceiling. When a switch is thrown so that a current exists in the spring, do the coils a. move closer together, b. move farther apart, or c. not move at all? d. Impossible to determine. 38. A long coaxial cable (cross section shown below) carries a current of $5.2\mathrm{A}$ flowing out of the page in the center conductor and an equal current flowing in the opposite direction in the shield. What is the magnetic field at point $P,15\mathrm{mm}$ from the center of the wire? Assume the center conductor is insulated from the shield by air. (a) $10.4\mathrm{T}$, (b) $2.08\times 10^{?4}\mathrm{T}$, (c) 0 , (d) it cannot be determined from the given information 39. A long coaxial cable (cross section shown below) carries a current of $5.2\mathrm{A}$ flowing out of the page in the center conductor and an equal current flowing in the opposite direction in the shield. What is the magnetic field at point $P,5\mathrm{mm}$ from the center of the wire? Assume the center conductor is insulated from the shield by air. (a) $10.4\mathrm{T}$, (b) $2.08\times 10?4\mathrm{T}$, (c) $20.8\mathrm{p}\times 10?7\mathrm{T}$, (d) it cannot be determined from the given information