With respect to the potential of emitter, base and collector, a NPN transistor conducts when

Options

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

Answer

To determine when an NPN transistor conducts with respect to the potential of the emitter, base, and collector, we can analyze the configuration of the transistor and the conditions required for it to operate in the active region.

### Step-by-Step Solution:

1. **Understanding the NPN Transistor Structure**:
- An NPN transistor consists of two n-type semiconductor materials (the emitter and collector) and one p-type material (the base).
- The emitter (E) is heavily doped with n-type material, the base (B) is lightly doped with p-type material, and the collector (C) is moderately doped with n-type material.

2. **Forward Biasing the Emitter-Base Junction**:
- For the NPN transistor to conduct, the emitter-base junction must be forward-biased. This means that the emitter must be at a lower potential than the base.
- In terms of voltage, this can be expressed as:
\[ V_E < V_B \]
- This condition allows current to flow from the emitter to the base.

3. **Reverse Biasing the Collector-Base Junction**:
- The collector-base junction must be reverse-biased for the transistor to operate in the active region. This means that the collector must be at a higher potential than the base.
- In terms of voltage, this can be expressed as:
\[ V_C > V_B \]
- This condition allows the majority carriers (electrons in the case of NPN) to flow from the emitter to the collector through the base.

4. **Combining the Conditions**:
- Therefore, for an NPN transistor to conduct, the following conditions must be satisfied:
\[ V_E < V_B < V_C \]
- This means that the emitter is at a lower potential than the base, and the collector is at a higher potential than the base.

### Conclusion:
The NPN transistor conducts when the potential of the emitter is less than that of the base, and the potential of the collector is greater than that of the base. Thus, the correct relationship is:
\[ V_E < V_B < V_C \]