General exam question G6B10
Subelement G6, CIRCUIT COMPONENTS· Group G6B
How does a ferrite bead or core reduce common-mode RF current on the shield of a coaxial cable?
- A.By creating an impedance in the current’s path (correct answer)
- B.It converts common-mode current to differential mode current
- C.By creating an out-of-phase current to cancel the common-mode current
- D.Ferrites expel magnetic fields
WhyA ferrite bead or core reduces common-mode RF current on a coaxial cable's shield by creating an impedance in the current's path. A ferrite bead or core slipped over a coaxial cable's shield adds series impedance specifically in the path that common-mode current on the outside of the shield would otherwise take, choking that unwanted current down without affecting the desired signal flowing inside the coax, answer A. It doesn't convert common-mode current into differential-mode current, doesn't work by generating a cancelling out-of-phase current, and ferrites don't "expel" magnetic fields, so B, C, and D misdescribe the mechanism.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2023-2027 NCVEC Element 3 pool (public domain); the explanation above is original writing, see our methodology.
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