Which component stores energy in a magnetic field and is commonly used in filter and timing circuits?

• A. Inductor
• B. Capacitor
• C. Diode
• D. Resistor

Answer: (A)

Energy storage in a magnetic field is provided by an inductor. An inductor uses a coil through which current flows to create a magnetic field, and the stored energy follows E = 1/2 L I^2. This magnetic energy allows the inductor to oppose changes in current, giving it a distinctive reactive property (X_L = 2πfL) that helps shape signal frequencies in filter networks. In timing contexts, inductors participate in circuits that control how voltages rise and fall or in LC oscillators where energy moves between magnetic and electric fields to create a timing or frequency reference. This is different from capacitors, which store energy in an electric field (E = 1/2 C V^2) and are more commonly associated with RC timing elements. Diodes and resistors don’t store energy in fields—diodes regulate current flow and resistors dissipate energy as heat. So, the component that stores energy in a magnetic field and is widely used in filter and timing circuits is the inductor.