A capacitor and an inductor do the same job — store energy and give it back — yet they do it in completely different fields. Here they are side by side: charge on plates versus current through a coil.
A capacitor and an inductor are the two components a circuit uses to store energy. The capacitor is two plates with a gap between them; the inductor is a coil of wire. Both take energy from a source, hold it, and release it again later — and this page puts them side by side to make the one key difference obvious: the field in which each keeps its energy.
Because their behaviour looks opposite in every practical way. A capacitor resists a change in voltage; an inductor resists a change in current. A capacitor blocks steady current while letting changing signals pass; an inductor does much the opposite. Once you see that one stores its energy in an electric field and the other in a magnetic field, those opposite behaviours stop being things to memorise and become easy to picture.
The left half shows the capacitor: two plates with charges on them and a uniform electric field between. The right half shows the inductor: a coil with current through it and a magnetic field looping around. A dashed line and a vs badge split the two. At the bottom, the two energy formulas make the parallel clear.
A source pushes current into each device. Neither one burns the energy up the way a resistor does; instead each holds it, ready to give it back. That shared purpose is the reason they are compared — and the reason their differences are so revealing.
The capacitor is two conducting plates separated by a gap. Connect it to the source and positive charge collects on one plate while negative collects on the other. The bigger the applied voltage, the more charge accumulates, until the plate voltage matches the source and no more steady current flows.
Between the two oppositely charged plates a uniform electric field forms, shown by the evenly spaced lines. This field is where the capacitor's energy actually lives, and because both charge and voltage grow together the stored energy climbs as the square of the voltage: E = ½CV².
The inductor is a coil of wire. Drive current through it and the moving charge creates a magnetic field, looping around and through the coil. That field is where the inductor's energy lives, and since the field grows with current, the stored energy goes as the square of the current: E = ½LI².
Because they store energy in different fields, they react to change in opposite ways. The capacitor holds voltage steady and resists sudden voltage changes; the inductor keeps current flowing and resists sudden current changes. That is why capacitors are used to smooth voltages and inductors to smooth currents — two tools, one idea of "storing energy in a field".
Where they store the energy. A capacitor stores it in the electric field between two charged plates; an inductor stores it in the magnetic field around a current-carrying coil. That single difference explains almost everything else about how each behaves.
No. Both store energy and then give it back, rather than burning it up the way a resistor does. In an ideal device the energy can be returned to the circuit, which is why they are called reactive components.
Because of the insulating gap between its plates. Charge gathers on the plates until the voltage matches the source, and then no steady current can cross the gap — so a capacitor blocks direct current but lets changing signals through.
A change in current changes the magnetic field around the coil, and that changing field pushes back against the change. The larger the inductance, the harder it is to change the current quickly.
Neither is inherently bigger. A capacitor's store goes as one half C V squared, an inductor's as one half L I squared, so it depends on the parts and the voltage or current — not on the type of device.