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An air-cored coil is preferred to an iron-cored one at radio frequency because iron

  • A.would suffer heavy eddy current and hysteresis loss
  • B.has too low a permeability at high frequency to be useful
  • C.would make the inductance depend on the current
  • D.cannot be laminated finely enough to be manufactured

Answer: A

Both losses rise steeply with frequency, so an iron core that is efficient at fifty hertz becomes a resistor at a megahertz. Ferrites, which are ceramic and of high resistivity, fill the gap where a core is needed at radio frequency.

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