What is active region for transistor?

Answer

### Step-by-Step Solution:

1. **Definition of Active Region**:
The active region of a transistor is the operational state where the transistor can amplify signals. It lies between the cut-off region and the saturation region.

2. **Understanding Cut-off and Saturation**:
- **Cut-off Region**: In this region, the transistor is off, meaning no current flows through it. This occurs when the base-emitter junction is reverse-biased.
- **Saturation Region**: In this region, the transistor is fully on, allowing maximum current to flow. This occurs when both the base-emitter and collector-base junctions are forward-biased.

3. **Biasing of Junctions in Active Region**:
- In the active region, the **base-emitter junction** is forward-biased, allowing current to flow from the emitter to the base.
- The **collector-base junction** is reverse-biased, preventing current from flowing from the collector to the base.

4. **Functionality in Active Region**:
- The transistor operates as an amplifier in this region. It can take a small input current at the base and control a larger output current flowing from the collector to the emitter.

5. **Summary**:
The active region is crucial for the amplification function of the transistor, allowing it to control large currents with smaller input signals.