Final answer:
To protect against spikes and sags in AC power, surge protectors use large inductance as a filter for high-frequency noise and circuit breakers to interrupt excessive current. Additionally, GFCIs prevent shock by detecting current loss, and isolation transformers provide insulation from the source.
Step-by-step explanation:
To safeguard a computer system from spikes (surges) and sags in AC power, devices such as surge protectors are employed. These surge protectors often use both inductance and capacitance, forming LC filters to guard against high-frequency noise which can damage computers. The plug-in unit designed to prevent this damage typically uses a large inductance in series with the computer to filter out such high frequencies, because inductors resist changes in current that are associated with high-frequency noise.
Inductive reactance, which increases with frequency, is the mechanism through which inductors prevent high-frequency AC current from passing through. Fuses and circuit breakers also provide protection by interrupting excessive currents to prevent thermal hazards. Devices such as GFCIs (Ground Fault Circuit Interrupters) and isolation transformers further contribute to a secure power supply by preventing shock and insulating the device from undesirable electrical paths.