Which electrical property opposes changes in current?

• A. Capacitance
• B. Reactance
• C. Inductance
• D. Resistance

Answer: (C)

Inductance is the property that resists changes in current. When current through a coil changes, it creates a changing magnetic flux, and this changing flux induces an emf that opposes the change (v = L di/dt). The negative sign from Lenz’s law means the induced voltage acts to oppose the alteration of current: if the current tries to rise quickly, the inductor generates a voltage that slows the rise; if it tries to fall, it generates a voltage that tends to keep it up. Energy is stored in the magnetic field around the coil, which is why this opposition occurs. Capacitance resists changes in voltage, not current; resistance opposes current flow in general, and reactance describes opposition to AC current in reactive elements, but the specific property that opposes changes in current is inductance.