Question

In the active region of transistor amplifier, which of the following options are correct :
• [A.] Base-emitter junction is forward-biased
• [B.] Base-emitter junction is reverse-biased
• [C.] Collector-base junction is forward-biased
• [D.] Collector-base junction is reverse biased Choose the correct answer from the options given below :

• A. A and C
• B. B and C
• C. A and D
• D. B and D

Hint:

For BJT operation:
• Active region: \[ BE \rightarrow \text{Forward biased} \] \[ CB \rightarrow \text{Reverse biased} \]
• Saturation region: Both junctions forward biased
• Cut-off region: Both junctions reverse biased

Answer 1

The Correct Option is C

Concept: A Bipolar Junction Transistor (BJT) operates in different regions depending on the biasing of its two PN junctions:
• Base-Emitter (BE) junction
• Collector-Base (CB) junction The major operating regions are:
• Cut-off region
• Active region
• Saturation region For amplifier operation, transistor must operate in the active region.

Step 1: Understand the condition for active region. In active region:
• Base-emitter junction must be forward biased.
• Collector-base junction must be reverse biased. This condition allows:
• Proper carrier injection from emitter.
• Proper collection of carriers by collector.
• Linear amplification action.

Step 2: Analyze statement A. Statement A says: \[ \text{Base-emitter junction is forward biased} \] This is absolutely correct because:
• The emitter must inject majority carriers into the base.
• Forward bias reduces barrier potential.
• Current flow becomes possible. Hence: \[ A \text{ is correct} \]

Step 3: Analyze statement B. Statement B says: \[ \text{Base-emitter junction is reverse biased} \] This is incorrect because:
• Reverse bias prevents emitter current injection.
• Transistor cannot work properly as an amplifier. Hence: \[ B \text{ is incorrect} \]

Step 4: Analyze statement C. Statement C says: \[ \text{Collector-base junction is forward biased} \] This condition occurs in saturation region, not in active region. Therefore: \[ C \text{ is incorrect} \]

Step 5: Analyze statement D. Statement D says: \[ \text{Collector-base junction is reverse biased} \] This is correct because:
• Reverse bias helps sweep carriers into collector region.
• Collector current becomes controlled by base current.
• Amplification becomes possible. Hence: \[ D \text{ is correct} \]

Step 6: Write final answer. Correct statements are: \[ A \text{ and } D \] Thus the correct option is: \[ \boxed{(C)} \]