*Question G6B10:
How does a ferrite bead or core reduce common-mode RF current on the shield of a coaxial cable?*  

*Correct Answer is  A: By creating an impedance in the current’s path*  

### AI Response: (may contain errors)  

A ferrite bead or core is used to reduce common-mode RF current on the shield of a coaxial cable by creating an impedance in the current’s path. Here's why:

1. **Correct Answer: A - By creating an impedance in the current’s path**
   - Ferrite materials have high permeability, which allows them to create a significant impedance to RF currents. When a ferrite bead or core is placed around a coaxial cable, it increases the inductive reactance to common-mode currents. This impedance effectively reduces the amplitude of these unwanted currents, helping to prevent interference and improve signal integrity.

2. **Why the other choices are incorrect:**
   - **B: It converts common-mode current to differential mode current**
     - This is incorrect because ferrite beads do not convert current modes. They simply impede the flow of common-mode currents without affecting the differential mode currents that carry the desired signal.
   - **C: By creating an out-of-phase current to cancel the common-mode current**
     - Ferrite beads do not generate out-of-phase currents. Instead, they provide a resistive and inductive impedance that dissipates the energy of the common-mode currents as heat.
   - **D: Ferrites expel magnetic fields**
     - This is incorrect because ferrites do not expel magnetic fields. They actually concentrate magnetic fields within themselves, which is why they are effective at creating impedance to RF currents.

In summary, the primary function of a ferrite bead or core is to increase the impedance to common-mode RF currents, thereby reducing their amplitude and mitigating potential interference.