Definition
The opposition that a capacitor offers to alternating current (AC), measured in ohms. Capacitive reactance decreases as the frequency of the AC or the capacitance of the capacitor increases, and is calculated as Xc = 1 / (2πfC), where f is frequency in hertz and C is capacitance in farads.
Plain English
Xc is how much a capacitor pushes back against alternating current. The faster the current alternates, or the bigger the capacitor, the less it pushes back.
Context Anchor
Seen in aircraft electrical theory, avionics circuits, filter circuits, and maintenance troubleshooting involving capacitors.
Derivation
X is the standard electrical engineering symbol for reactance (opposition to AC that comes from storing energy rather than dissipating it). The lowercase c stands for capacitive. Together, Xc means 'reactance from a capacitor,' distinguishing it from XL (inductive reactance from a coil).
Why Pilots Care
Helps maintain proper operation of AC-powered avionics and instruments.
Grounding Statement
When the current changes direction faster, a capacitor resists it less, so Xc goes down.
Intuition Check
Xc is not ordinary fixed resistance. It is opposition caused by a capacitor, and its value changes with the circuit’s frequency and capacitance.
Example Sentence 1
The technician calculated Xc for the filter capacitor at 400 hertz to confirm the circuit would pass the signal cleanly.
Example Sentence 2
The technician checked Xc values while troubleshooting the electrical system.