The phase shift is the time difference between two periodic signals, usually expressed as an angle in degrees or radians.
Think of two sinusoidal signals with the same frequency. Their peaks and zero crossings may coincide or appear shifted in time.
That time difference between the passage of one and the passage of the other is called Phase Shift (𝜑). It is measured in degrees.
Let’s see how each component behaves individually.
| Component | Symbol | Phase Shift | CIVIL Rule | Effect |
|---|---|---|---|---|
| Resistor | R | (In phase) | - | Dissipates energy (Heat) |
| Capacitor | C | Leads | C I V | Stores electric field |
| Coil | L | Lags | V I L | Stores magnetic field |
The Resistor (R)
The resistor does not store energy. It dissipates it instantly as heat. Therefore, it has no “inertia.” It doesn’t need time to charge or discharge.
- Behavior: If Voltage rises, Current rises instantly. If Voltage is zero, Current is zero.
- Phase Shift: 0º. We say they are In Phase.
The Coil (L)
Remember that the coil opposes changes in current according to Lenz’s law. When we apply AC Voltage (we start pushing), the current takes time to start because the coil resists.
- Behavior: First, the Voltage arrives (the push), and some time later, the Current manages to rise.
- Phase Shift: The Current LAGS 90º behind the Voltage.
The Capacitor (C)
The capacitor works in reverse. It is a tank that needs to be filled. Think of a tank: for its level (voltage) to change, fluid must first flow in or out (current).
You cannot have pressure (Voltage) if you haven’t introduced charge first.
- Behavior: First, the Current flows (filling), and as a consequence, the Voltage rises afterwards.
- Phase Shift: The Current LEADS 90º ahead of the Voltage.
How Phase Shift Affects Power
Phase shift modifies the average power transferred by an alternating signal.
Power is
- If V and I are in sync (Resistor), when you multiply positive by positive, you get Positive Power (Useful work).
- But if they are 90º out of phase (Ideal Coil/Capacitor), there are moments when Voltage is positive and Current is negative. Positive times negative = Negative.
- That means Negative Power.
- The component is not consuming energy; it is returning it to the grid.
The Coil and Capacitor spend their time borrowing energy and returning it in the next half-cycle. They don’t consume real energy, but they load the cables with useless current.
