A `npn` transistor conducts when

Options

A. collector is positive and emitter is at same potential as the base
B. both collector and emitter are negative with respect to the base
C. both collector and emitter are positive with respect to the base
D. collector is positive and emitter is negative with respect to the base

Answer

To determine when an NPN transistor conducts, we need to understand its structure and the conditions required for it to operate in the active region. Here’s a step-by-step explanation:

### Step 1: Understand the Structure of NPN Transistor
An NPN transistor consists of two n-type semiconductor materials (the collector and emitter) and one p-type semiconductor material (the base).

### Step 2: Identify the Biasing Conditions
For an NPN transistor to conduct, the following conditions must be met:
- The emitter must be at a lower potential than the base (forward-biased junction).
- The collector must be at a higher potential than the base (reverse-biased junction).

### Step 3: Emitter-Base Junction
The emitter-base junction must be forward-biased. This means:
- The emitter (n-type) should be more negative relative to the base (p-type).

### Step 4: Collector-Base Junction
The collector-base junction must be reverse-biased. This means:
- The collector (n-type) should be more positive relative to the base (p-type).

### Step 5: Conclusion
Combining the above conditions, an NPN transistor conducts when:
- The collector is positive with respect to the base.
- The emitter is negative with respect to the base.

### Final Answer
An NPN transistor conducts when the collector is positive and the emitter is negative with respect to the base.

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