Which of the following best describes a Faraday cage?

• A. A device that stores magnetic energy
• B. A device converting AC to DC
• C. A type of wire wound coil
• D. A cage or enclosure that blocks electromagnetic fields

Answer: (D)

Shielding from electric and magnetic fields is the main idea. A Faraday cage is a conducting enclosure that responds to external electric fields by moving charges on its outer surface in just the right pattern to cancel the field inside. Because of this, the interior stays shielded from external electromagnetic fields, including many radiofrequency signals. For effective shielding of time-varying fields, the enclosure should be closed with no significant gaps, and any openings should be much smaller than the wavelength of the incident waves so little energy can leak through.

This isn’t about storing magnetic energy, converting AC to DC, or winding a coil. Those describe different devices. The closest and best description is a cage or enclosure that blocks electromagnetic fields.