A) Negligible input resistance and high output resistance
B) High input resistance and low output resistance
C) Medium input resistance and high output resistance
D) Low input resistance as well as output resistance
✅ Answer: C) Medium input resistance and high output resistance
💡 Detailed Explanation
A transistor can be connected in three basic configurations:
Common Base (CB)
Common Emitter (CE)
Common Collector (CC)
In the common emitter (CE) configuration, the emitter terminal is common to both the input and output circuits.
The input is applied between:
Base → Emitter
The output is taken between:
Collector → Emitter
🔹 Input Resistance
The input resistance of a CE transistor configuration is medium compared with the other two configurations.
Typically:
CE input resistance = Medium
This is because the input is applied to the forward-biased base-emitter junction.
🔹 Output Resistance
The output is obtained from the collector circuit. The collector-base junction is reverse biased, resulting in a relatively high output resistance.
Therefore:
CE output resistance = High
📊 Comparison of Transistor Configurations
| Configuration | Input Resistance | Output Resistance | Current Gain |
|---|---|---|---|
| Common Base (CB) | Low | High | Less than 1 |
| Common Emitter (CE) | Medium | High | High |
| Common Collector (CC) | High | Low | High |
📌 Remember Points
➤ Common Base: Low input resistance, High output resistance
➤ Common Emitter: Medium input resistance, High output resistance
➤ Common Collector: High input resistance, Low output resistance
⚡ Exam Shortcut:
CE → Medium Input Resistance + High Output Resistance
✅ Final Answer
C) Medium input resistance and high output resistance