What is the primary difference between AC and DC methods in electromagnetic testing?

The primary difference between AC and DC methods in electromagnetic testing lies in the nature of the current used: AC (alternating current) fluctuates in magnitude and direction, while DC (direct current) flows steadily in one direction. This fundamental distinction plays a critical role in how each method interacts with the conductive materials being tested.

In electromagnetic testing, AC is often utilized because it generates changing magnetic fields that are effective for detecting flaws and discontinuities in materials, particularly in methods like eddy current testing. The alternating nature of the current allows for profiles of electrical conductivity and permeability to be assessed, which is particularly valuable in detecting surface and near-surface defects.

On the other hand, DC is generally used in applications where continuous monitoring is needed or in specific testing scenarios where the effects of AC might not be desired. Each method has its unique advantages and is chosen based on the particular requirements of the testing environment.

The other options suggest comparisons that do not accurately represent the core differences or applicability of AC versus DC in electromagnetic testing. For instance, while it is accurate that AC can be used in eddy current testing, DC is not inherently more widely applicable; its use case is more limited compared to AC. The speed of testing can vary based on the specific material