How Do Inductors and Capacitors Work in Electrical Circuits?
FAQs on Main Differences Between Inductor and Capacitor
1. What is the main difference between an inductor and a capacitor?
Inductors and capacitors are electronic components with opposite functions: an inductor stores energy in a magnetic field, while a capacitor stores energy in an electric field.
Key differences include:
- Inductors oppose changes in current; capacitors oppose changes in voltage.
- Inductors use coils of wire; capacitors use plates separated by a dielectric.
- Measured in henry (H) for inductors and farad (F) for capacitors.
- Inductors pass DC easily, block high-frequency AC; capacitors block DC, pass high-frequency AC.
2. How do capacitors and inductors store energy differently?
Capacitors store energy as an electric field between two plates, while inductors store energy in the form of a magnetic field generated by current flow.
For students:
- Capacitor: Energy (E) = 1/2 CV2
- Inductor: Energy (E) = 1/2 LI2
- Capacitors oppose changes in voltage, inductors oppose changes in current.
3. What are the main applications of inductors and capacitors?
Inductors and capacitors are both used widely in electrical and electronic circuits, but for different purposes.
- Inductors: Used in filters, transformers, chokes, and energy storage in power supplies.
- Capacitors: Used in timing circuits, filters, energy storage, coupling/decoupling, and tuning circuits.
4. Can you list the similarities between inductors and capacitors?
Inductors and capacitors share some common characteristics as passive components in circuits.
- Both can store energy—inductors as magnetic energy, capacitors as electric energy.
- Both cause a phase difference between current and voltage in AC circuits.
- They are essential in tuning, filtering, and oscillating circuits.
5. How does a capacitor behave in a DC and an AC circuit?
Capacitors behave differently in DC and AC circuits:
- In DC circuits, a capacitor initially allows current, then blocks it once charged (acts like an open circuit in steady state).
- In AC circuits, capacitors continuously charge and discharge, allowing AC current to pass more easily as frequency increases.
6. How does an inductor behave in a DC and an AC circuit?
Inductors behave as follows in different circuits:
- In DC circuits, an inductor initially resists changes in current but eventually acts like a short circuit (allows DC current after steady state).
- In AC circuits, inductors resist high-frequency changes, causing greater reactance as frequency increases (blocking high-frequency AC).
7. Why are inductors and capacitors known as reactive components?
Inductors and capacitors are termed reactive components because they store and release energy but do not dissipate it as heat.
This causes the current and voltage to shift out of phase:
- Inductors: cause current to lag voltage.
- Capacitors: cause current to lead voltage.
8. How do inductors and capacitors react to sudden changes in voltage or current?
Inductors resist sudden changes in current, while capacitors resist sudden changes in voltage.
- If current changes quickly, the inductor generates a back EMF (opposing voltage).
- If voltage changes quickly, the capacitor tries to keep the voltage across its plates constant.
9. What are the SI units of inductance and capacitance?
Inductance is measured in henry (H), while capacitance is measured in farad (F).
Always remember:
- SI unit of inductance: henry (H)
- SI unit of capacitance: farad (F)
10. Which has polarity: inductor or capacitor?
Capacitors can have polarity (especially electrolytic capacitors), while inductors do not inherently have polarity.
- Polarised capacitors: Electrolytic, tantalum types need to be connected in correct orientation.
- Inductors can be connected in any direction in a circuit for basic operation.






















