Consider the following statements regarding Analog Circuits – Transistor:1.A BJT operates in active region when base-emitter junction is forward biased and collector-base junction is reverse-biased.2.Current gain of transistor is defined as ratio of collector current to base current.3.Transistor can be used as amplifier in active region.4.In saturation region, transistor acts as open switch.Which of the above statements is/are correct?

Correct Answer: C - 1, 2 and 3 only

Quick Concept Explanation

A BJT used as a linear amplifier is biased in the active region: the base-emitter junction is forward biased and the collector-base junction reverse biased. In saturation both junctions are forward biased and the transistor behaves approximately as a closed switch, not an open switch.

Exam focus: Active region for amplification; cutoff/saturation for switching. Common trap: Saturation corresponds to ON/closed-switch behavior.

Statement-wise Verification

• Statement 1 - Correct.
  A BJT operates in active region when base-emitter junction is forward biased and collector-base junction is reverse-biased.
  A BJT used as a linear amplifier is biased in the active region: the base-emitter junction is forward biased and the collector-base junction reverse biased.
• Statement 2 - Correct.
  Current gain of transistor is defined as ratio of collector current to base current.
  Common-emitter current gain β is IC/IB.
• Statement 3 - Correct.
  Transistor can be used as amplifier in active region.
  A BJT used as a linear amplifier is biased in the active region: the base-emitter junction is forward biased and the collector-base junction reverse biased.
• Statement 4 - Incorrect.
  In saturation region, transistor acts as open switch.
  A saturated BJT is approximately an ON/closed switch; cutoff corresponds to open-switch behavior

Core Concept

A BJT used as a linear amplifier is biased in the active region: the base-emitter junction is forward biased and the collector-base junction reverse biased. Common-emitter current gain β is IC/IB. In saturation both junctions are forward biased and the transistor behaves approximately as a closed switch, not an open switch.

Formula / Key Relationship

β=I_C/I_B; I_E=I_C+I_B.

Why the Other Options Are Wrong

Option A is incorrect because it omits correct statement(s) 2. Option B is incorrect because it includes incorrect statement(s) 4 and omits correct statement(s) 2, 3. Option D is incorrect because it omits correct statement(s) 1.

Exam Shortcut / Approach

Active region for amplification; cutoff/saturation for switching.

Common Mistake

Saturation corresponds to ON/closed-switch behavior.

Quick Revision

BJT Active and Saturation Regions is linked with BJT Operating Regions, BJT and Analog Electronics. Active region for amplification; cutoff/saturation for switching.