Alternating Current (AC Circuits, LCR & Power Factor) | AC vs DC Guide

Alternating Current (AC Circuits, LCR & Power Factor)

Understand AC vs DC current, LCR circuit behavior, power factor correction, and AC‑to‑DC conversion techniques.

⚡ What Is Alternating Current (AC)?

Alternating current (AC) reverses direction periodically. Many power grids and household outlets rely on AC. Devices like transformers and motors work efficiently with AC.

🔍 Difference Between AC and DC Current

Here’s a clear comparison of ac and dc current:

PropertyAC CurrentDC Current
FlowReverses direction periodicallyFlows in one direction
GenerationAC generators (alternators)Batteries, solar cells
TransmissionHigh voltage with low lossDC transmission uses inverters
ExamplesHousehold outlets, grid powerPhones, laptops, LED lights
ConversionRequires rectifiers to convertEasier to store in batteries

In summary: AC suits transmission, DC suits storage and electronics.

🔁 AC Voltage and Current in LCR Circuits

LCR (inductor‑capacitor‑resistor) circuits demonstrate phase relationships between current and voltage. AC behavior depends on reactance.

  • Capacitive reactance: \( X_C = \frac{1}{2\pi f C} \)
  • Inductive reactance: \( X_L = 2\pi f L \)
  • Impedance: \( Z = \sqrt{R^2 + (X_L – X_C)^2} \)
  • Phase angle: \( \phi = \tan^{-1}\left(\frac{X_L – X_C}{R}\right) \)
Example: In a circuit with R = 10 Ω, L = 50 mH, C = 10 µF at 60 Hz: \( X_L = 2π60×0.05 = 18.85 Ω \), \( X_C = 1/(2π60×10×10^{-6}) = 265 Ω \). Impedance ≈ 264 Ω, current lags voltage.
LCR Circuit Phasor Diagram
Figure: LCR Circuit Phasor Diagram showing the phase relationship between voltage and current.

🔧 Power Factor & Power in AC Circuits

Power factor (PF) measures efficiency in AC circuits. A PF close to 1 means effective power use.

  • Real power: \( P = VI\cos \phi \)
  • Apparent power: \( S = VI \)
  • Reactive power: \( Q = VI\sin \phi \)
Example: If V = 230 V, I = 5 A, and φ = 30°: P = 230×5×cos 30° ≈ 995 W.

🔄 Converting AC to DC Current

Most electronic devices need DC. You can convert AC to DC using:

  • Rectifier circuits: diodes convert AC to pulsed DC.
  • Capacitor filters: smooth the pulsating output.
  • Voltage regulators: deliver steady DC voltage.
Example: A bridge rectifier with a capacitor filter outputs ~310 V DC from 220 VAC.

🛠️ AC‑to‑DC Current Converter Tool

Embed a basic online tool to illustrate AC‑to‑DC conversion in action:



Estimated DC Output: — V

🧠 Real‑World Applications

  • Household electricity uses AC distribution.
  • Battery‑powered devices rely on internal rectification from AC to DC current.
  • Industrial motors and transformers run on AC.
  • Power factor correction saves energy in factories.

Power Factor Calculator

Enter Real and Apparent Power to calculate power factor.





Power Factor (cos φ): –

LCR Resonant Frequency Calculator

Enter inductance (L) and capacitance (C) to compute resonance frequency.





Resonant Frequency: - Hz

📚 Common AC vs DC Current FAQs

1. What is the difference between AC and DC current?

AC current changes direction periodically, while DC current flows in one direction continuously.

2. Why do we transmit power using AC?

We transmit AC at high voltage to reduce losses. Transformers easily adjust AC voltage levels.

3. Can a device use AC & DC current?

Many devices plug into AC and convert it to DC internally using rectifier‑regulator circuits.

4. What is power factor?

Power factor equals real power divided by apparent power (cos φ). It measures AC circuit efficiency.

5. How do I convert AC to DC current?

You use a rectifier, capacitor, and regulator. A bridge rectifier plus filter delivers smooth DC.

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