What is the unit of electrical field strength used in RF exposure limits?

• A. Wavelength in meters.
• B. Ohms.
• C. Usually volts per meter (V/m) for electric field strength; sometimes specific absorption rate (SAR) or power density in W/m^2.
• D. Tesla.

Answer: (C)

Electric field strength is a measure of how intense the electric part of an electromagnetic wave is at a point, and its SI unit is volts per meter. In RF exposure limits, this unit is used because the electric field directly relates to how much potential difference a charge would experience per meter of distance, which governs how the field interacts with biological tissue. In many guidelines, exposure limits are stated as E-field values in V/m.

Some contexts use other quantities, like SAR (watts per kilogram) or power density (watts per square meter) to express exposure, but those refer to different aspects of how energy is absorbed or carried by the wave, not the electric field strength itself. The options you might see that don’t fit are wavelength (a length), ohms (impedance), and Tesla (magnetic flux density). Wavelength, resistance/impedance, and magnetic field are not the unit for electric field strength.