An n-p-n transistor has three leads A, B and C. Connecting B and C by moist fingers, A to the positive lead of an ammeter, and C to the negative lead of the ammeter, one finds large deflection. Then, A, B and C refer respectively

Options

A. Emitter, base and collector
B. Base, emitter and collector
C. Base, collector and emitter
D. Collector, emitter and base

Explanation

To solve the problem regarding the n-p-n transistor with leads A, B, and C, we need to identify which lead corresponds to the emitter, base, and collector based on the given conditions.

### Step-by-Step Solution:

1. **Understanding the NPN Transistor Configuration**:
- An n-p-n transistor consists of three layers: two n-type materials (the emitter and collector) and one p-type material (the base).
- The emitter is heavily doped, the base is lightly doped, and the collector is moderately doped.

2. **Connecting the Leads**:
- The problem states that lead B and C are connected by moist fingers, and lead A is connected to the positive terminal of an ammeter while lead C is connected to the negative terminal.
- This setup indicates that there is a current flow through the transistor, which is essential for identifying the leads.

3. **Analyzing the Current Flow**:
- In an n-p-n transistor, for the transistor to be in active mode, the base-emitter junction must be forward-biased. This means that the base (p-type) needs to be at a higher potential than the emitter (n-type).
- Since lead A is connected to the positive terminal of the ammeter, it is likely that lead A is the base, as it needs to be at a higher potential for forward bias.

4. **Identifying the Emitter and Collector**:
- Since lead A is identified as the base, we need to determine which of the remaining leads (B or C) is the emitter and which is the collector.
- The moist fingers connecting B and C suggest that there is a lower conductivity path, which indicates that one of these leads is likely the emitter (which is more conductive) and the other is the collector.

5. **Determining the Leads**:
- The lead connected to the negative terminal of the ammeter (C) must be the emitter because it is the n-type material that allows current to flow easily when forward-biased.
- This leaves lead B as the collector, which is also n-type but is less conductive compared to the emitter.

6. **Final Identification**:
- Therefore, we conclude:
- Lead A = Base
- Lead B = Collector
- Lead C = Emitter

### Conclusion:
The final identification of the leads is:
- A = Base
- B = Collector
- C = Emitter