Magnitude of magnetic field due to a long, straight wire (19-9)

Question 1 of 4

Question

Distance from the wire to the location where the field is measured

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Review

Equation 19-9 and the field properties shown in Figure 19-17 are strictly correct only if the wire is infinitely long. But they are very good approximations if the distance $r$ is small compared to the length of the wire.

The constant $\mu_0$ in Equation 19-9, called the permeability of free space for historic reasons, plays a role in magnetism that’s comparable to the role of the constant $\epsilon_0$ , the permittivity of free space, in electricity (see Section 16-6). Its value is exactly $\mu_0 = 4\pi \times 10^{-7}\ \mathrm{T} \cdot \mathrm{m}/\mathrm{A}$ .