Self-inductance and opposition to current change
An inductor stores energy in a magnetic field created by current flowing through it. When current increases through an inductor, the rising magnetic field induces an EMF that opposes the change, slowing the current's rise. When current decreases, the collapsing magnetic field induces an EMF that opposes the decrease, trying to sustain the current. This opposition to change is called self-inductance. Inductance depends on the geometry: coils with more turns have higher inductance, and compact coils have higher inductance than spread-out coils. The stored energy in an inductor carrying current I is one-half times L times I squared, where L is the inductance. This energy remains in the magnetic field as long as current flows, ready to be released if the current path is interrupted.
Inductors in circuits and energy management
Inductors smooth current changes and filter high-frequency signals from power supplies. When the supply voltage drops, the inductor releases stored energy to maintain current. When voltage spikes, the inductor absorbs energy, protecting downstream circuits. This energy management capability makes inductors essential in switching power supplies that regulate voltage efficiently. In AC circuits, inductors create frequency-dependent impedance, increasing with frequency, allowing them to block high-frequency noise while passing low frequencies. Transformers exploit mutual inductance, where current changes in one coil induce voltage in another. Resonant circuits containing inductors and capacitors oscillate at specific frequencies determined by their values, forming the basis of radios, wireless power transfer, and RF communication systems.