Heating in an electromagnetic field:

• A. Produces eddy currents in conductive substances
• B. Is a so-called current of capacity
• C. Is less effective in vascular type of tissue
• D. Is by a conduction current

Answer: (A)

When a changing electromagnetic field interacts with matter, the field induces circulating electric currents in conductive substances. In biological tissues, which conduct electricity via ions, these induced currents flow as eddy currents and dissipate energy as heat through resistance (Joule heating). This specific mechanism—eddy currents arising from a time-varying field—is the most direct explanation for heating in an electromagnetic field, which is why it’s the best answer.

Displacement current, related to a changing electric field in nonconductive media, isn’t the primary driver of heat in most practical tissue exposures. The idea that heating is universally less effective in vascular tissue isn’t a reliable rule, since heating depends on tissue conductivity and perfusion can modify the temperature change. Saying heating is by a generic conduction current doesn’t capture the distinctive looped patterns of eddy currents that produce the heat efficiently in conductive substances.