Question

How to identify DC?

Answer 1

To identify whether a signal or voltage is **DC (Direct Current)**, you can look for a few characteristics:

1. **Constant Polarity**:
   - In DC, the current flows in one direction only. If you're looking at a voltage or signal, a DC voltage will have a constant positive or negative value.
   - For example, a 5V DC power supply will always provide a steady 5V without any changes or fluctuations.

2. **No Change Over Time**:
   - A DC voltage or current doesn't change its magnitude or direction over time. If you observe the voltage with an oscilloscope or a multimeter, it will remain constant.
   
3. **Multimeter**:
   - If you use a **digital multimeter**, you can set it to measure **DC voltage (DCV)**. The display will show a constant value (e.g., 5V, -12V), indicating DC.

4. **Oscilloscope**:
   - If you use an **oscilloscope**, a DC signal will appear as a flat, straight line that doesn't move up and down.
   - You will see the signal staying at a constant level, either positive or negative, without any variation.

5. **Battery or Power Source**:
   - DC is typically supplied by sources like **batteries**, **DC power supplies**, or **solar cells**. So, if you're dealing with a battery (like a 9V or AA battery), it's a DC source.

### DC vs AC:
- **AC (Alternating Current)** varies in polarity (positive and negative) and amplitude (size), typically in a sinusoidal waveform. If you observe a signal with a regular rise and fall, it’s likely AC.
  
In short, if you see a signal that is steady and unchanging, it's DC.