What is the line integral of $\overrightarrow{B}\cdot \overrightarrow{ds}$ between points i and f in FIGURE EX29.19?

As a new electrical technician, you are designing a large solenoid to produce a uniform 0.150 T magnetic field near the center of the solenoid. You have enough wire for 4000 circular turns. This solenoid must be 55.0 cm long and 2.80 cm in diameter. What current will you need to produce the necessary field?

A closed curve encircles several conductors. The line integral $\oint B\cdot dl$ around this curve is $3.83\times {10}^{-4}\text{ T m}$. If you were to integrate around the curve in the opposite direction, what would be the value of the line integral? Explain.

A long, hollow wire has inner radius R₁ and outer radius R₂. The wire carries current I uniformly distributed across the area of the wire. Use Ampère's law to find an expression for the magnetic field strength in the three regions 0 < r < R₁, R₁ < r < R₂, and R₂ < r.

An infinitely wide flat sheet of charge flows out of the figure in FIGURE CP29.83. The current per unit width along the sheet (amps per meter) is given by the linear current density J_s. Find the magnetic field strength at distance d above or below the current sheet.

The value of the line integral of $\overrightarrow{B}\cdot \overrightarrow{ds}$ around the closed path in FIGURE EX29.21 is 1.38 x 10^-5 T m. What are the direction (into or out of the figure) and magnitude of I₃?

(I) A 2.5-mm-diameter copper wire carries a 28-A dc current (uniform across its cross section). Determine the magnetic field: (a) at the surface of the wire; (b) inside the wire, 0.50 mm below the surface; (c) outside the wire 2.5 mm from the surface.

You want to get an idea of the magnitude of magnetic fields produced by overhead power lines. You estimate that a transmission wire is about 12 m above the ground. The local power company tells you that the lines operate at 145 kV and provide a maximum of 45 MW to the local area. Estimate the maximum magnetic field you might experience walking under one such power line, and compare to the Earth’s field. [For an ac current, values are rms, and the magnetic field will be changing.]

Suppose the current in the coaxial cable of Problem 34, Fig. 28–45, is not uniformly distributed, but instead the current density j varies linearly with distance from the center: j₁ = C₁R for the inner conductor and j₂ = C₂R for the outer conductor. Each conductor still carries the same total current I₀, in opposite directions. Determine the magnetic field in terms of I₀ in the same four regions of space as in Problem 34.