Question

The region in the output voltage versus input voltage graph where a transistor can be used as an amplifier is?

• A. \text{active region}
• B. \text{cut-off region}
• C. \text{saturation region}
• D. \text{passive region} \

Hint:

For a transistor to function as an amplifier, it must be in the active region, where the base-emitter junction is forward biased and the base-collector junction is reverse biased.

Answer 1

The Correct Option is A

Step 1: Understanding Transistor Operating Regions
A bipolar junction transistor (BJT) operates in three main regions:
- Cut-off Region: Both junctions are reverse biased, and the transistor is OFF (no conduction).
- Saturation Region: Both junctions are forward biased, and the transistor is fully ON (used in switching applications).
- Active Region: The base-emitter junction is forward biased, and the base-collector junction is reverse biased. In this region, the transistor functions as an amplifier.
Step 2: Why the Active Region is Used for Amplification
In the active region:
- A small change in the input base current causes a large change in the output collector current.
- The transistor operates linearly, making it suitable for amplification.
Step 3: Why Other Options Are Incorrect
- Cut-off Region (Option 2): Incorrect, as the transistor is OFF and does not conduct.
- Saturation Region (Option 3): Incorrect, as the transistor is fully ON and cannot amplify signals.
- Passive Region (Option 4): Incorrect, as there is no such standard region in transistor operation.
Thus, the correct region where a transistor can be used as an amplifier is the active region. \bigskip