When eddy current testing a nonferrous specimen, a discontinuity will:

In eddy current testing, the presence of a discontinuity, such as a crack or void, in a nonferrous specimen affects the flow of eddy currents. Specifically, a discontinuity can disrupt the uniform conductivity within the material. When eddy currents encounter a defect, the effective path for these currents is altered, resulting in changes to the overall conductivity of the specimen.

When a discontinuity is present, it creates an area where the eddy currents cannot flow as freely. This disturbance leads to a reduction in the effective conductivity of the specimen, as the currents are impeded by the presence of the defect. Hence, a discontinuity will decrease the effective conductivity, which explains why the selected answer is correct.

In contrast, the other choices suggest an increase in conductivity or permeability, which does not accurately reflect the impact of a discontinuity on the eddy current flow in nonferrous materials. The fundamental principle is that defects typically disrupt the normal flow of electrical currents, leading to decreased conductivity rather than an increase.