When an n-p-n transistor is used as an amplifier, then

Options

A. electrons move from base to collector
B. electrons move from emitter to base
C. electrons move from collector to base
D. holes move from base to emitter

Answer

To solve the question about the operation of an NPN transistor when used as an amplifier, we need to understand the basic functioning of the NPN transistor in forward bias conditions.

### Step-by-Step Solution:

1. **Understanding NPN Transistor Structure**:
- An NPN transistor consists of three regions: the emitter (N-type), the base (P-type), and the collector (N-type). The emitter is heavily doped, while the base is lightly doped.

2. **Forward Biasing the Transistor**:
- When the NPN transistor is used as an amplifier, it is forward biased. This means that the emitter-base junction is forward biased, allowing current to flow easily from the emitter to the base.

3. **Movement of Charge Carriers**:
- In an NPN transistor, when the emitter is forward biased, electrons from the emitter (N-type) are injected into the base (P-type). This is because the emitter is at a higher potential than the base.

4. **Electron Movement**:
- The electrons that move from the emitter to the base are the majority carriers in the emitter and minority carriers in the base. This movement of electrons is crucial for the amplification process.

5. **Holes Movement**:
- As electrons move from the emitter to the base, they recombine with holes in the base. This results in the movement of holes from the base to the emitter, as the holes are the majority carriers in the base region.

6. **Conclusion**:
- Therefore, when an NPN transistor is used as an amplifier, the correct statements are:
- Electrons move from the emitter to the base.
- Holes move from the base to the emitter.

### Final Answer:
- The correct options are:
- Electrons move from emitter to base.
- Holes move from base to emitter.