Question

Direction for Assertion - Reason type questions (A) If both Assertion and Reason are true and reason is the correct explanation of assertion. (B) If both Assertion and Reason are true but Reason is not the correct explanation of assertion. (C) If Assertion is true but Reason is false (D) If both assertion and reason are false A : A transistor amplifier circuit in common emitter configuration has low input impedance \(\mathrm{R}\) : Base-emitter junction is forward biased (A) (B) (C) (D)

Short answer

The correct option is (A), as both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Step-by-step solution

Check the Assertion

The Assertion states that a transistor amplifier circuit in common emitter configuration has low input impedance. In a common emitter configuration, the emitter of the transistor is the common terminal to both input and output terminals. The input impedance for a common emitter configuration is indeed relatively low compared to other configurations like common base or common collector. Hence, the Assertion is true. #Step 2: Determine if the Reason is true or false#

Check the Reason

The Reason states that the base-emitter junction is forward biased in the common emitter configuration. In a transistor amplifier circuit, the base-emitter junction being forward biased means that the base current flows into the base terminal, and the transistor operates in the active mode. This is a necessary condition for the common emitter configuration to function as an amplifier. Hence, the Reason is true. #Step 3: Determine if the Reason is the correct explanation of the Assertion#

Determine the correlation

The input impedance in a common emitter configuration depends on several factors, such as the transistor parameters and external resistors. However, low input impedance is mainly due to the base-emitter junction being forward biased. When the base-emitter junction is forward biased, it allows a significant amount of current to flow into the base terminal, which results in a low input impedance. Therefore, the Reason is indeed the correct explanation for the Assertion. #Step 4: Choose the correct option#

Answer the question

Since both Assertion and Reason are true, and Reason is the correct explanation of Assertion, the correct option is (A).

Key concepts

Common Emitter Configuration

A Common Emitter Configuration is a popular setup for transistor amplifiers, widely utilized due to its ability to amplify voltage significantly. In this arrangement, the emitter terminal of the transistor is common to both the input and output circuits. This configuration provides a phase shift of 180 degrees between the input and output signals.

The common emitter amplifier is favored for several applications due to its medium input and output impedance levels. It offers a high voltage gain, making it a suitable choice for the amplification of weak signals in various electronic devices.

• Provides good voltage gain
• Used in audio amplifiers and RF transmissions
• Phase inversion is a characteristic feature

Understanding the common emitter configuration's characteristics allows engineers and students to apply this knowledge in practical electronic circuit design efficiently.

Input Impedance

Input Impedance is a crucial parameter in the analysis and design of transistor amplifiers, such as those in common emitter configuration. The input impedance of a common emitter setup is relatively low, which is why this configuration is considered effective for current amplification.

This low impedance results from the forward biasing of the base-emitter junction: allowing significant current flow through the base.

• Low input impedance implies that a smaller input signal is sufficient to drive the amplifier.
• Useful in the amplification of weak signals due to its low input resistance.
• Affects how the amplifier couples with preceding stages in a circuit.

By understanding input impedance, engineers can plan circuits that properly pair the signal source with the amplifier, ensuring optimal performance and efficiency.

Base-Emitter Junction

The Base-Emitter Junction is a key component in a transistor's operation, especially in amplifier circuits like the common emitter configuration. This junction acts like a diode, allowing current to flow only when it is forward biased.

In the active region of a transistor operation, which is where amplification occurs, the base-emitter junction is purposefully forward biased. It is crucial for effective amplification as it regulates current flow from the base to the emitter, controlling the larger current flow between the collector and emitter.

• Forward biased allows base current to control collector current.
• This modulation forms the basis of amplification.
• Key factor influencing input impedance.

Proper understanding of the base-emitter junction's behavior is essential for designing effective amplifier circuits and ensuring their efficient operation.

Forward Biasing

Forward Biasing in the context of transistor amplifiers is vital to the functionality of configurations such as the common emitter. When the base-emitter junction is forward biased, it allows a minimal base current to control a much larger collector current.

Forward biasing not only enables amplification but also helps in determining the operating point and stability of the transistor. In a common emitter configuration, forward biasing is what makes the input stage active, lowering the input impedance and allowing the transistor to function efficiently.

• Ensures transistor is in active mode for amplification.
• Directly affects input impedance and gain characteristics.
• Necessary for the transistor to switch on and conduct.

By comprehending the principle of forward biasing, students and engineers can better understand how to control and optimize transistor-based circuits.