Which of the following is a common source of electromagnetic interference (EMI) for twisted pair cables?

Electromagnetic interference (EMI) can disrupt the performance of twisted pair cables, which are commonly used in networking. One of the significant sources of EMI is power lines. Power lines carry high amounts of electrical current, which generates electromagnetic fields. These fields can induce noise and signal degradation in nearby cables, including twisted pair cables. The closely twisted design of these cables helps to mitigate some of this interference, but being in proximity to high-voltage power lines can still lead to noticeable disruption in their signal quality.

In contrast, smartphones can occasionally emit radio frequency interference, but their impact is less direct and typically more localized compared to the constant and strong electromagnetic fields generated by power lines. Fiber optic cables are immune to EMI since they transmit data using light rather than electrical signals. Lastly, switches do not generate significant electromagnetic interference themselves; rather, they are passive devices that facilitate network connections, and any signals they handle are typically very low in EMI impact. Thus, power lines remain the primary source of interference that affects twisted pair cables.