Question

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 to :

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

Answer 1

The Correct Option is A

To determine the correct identification of the leads in an $n-p-n$ transistor, we need to analyze the experiment described in the question.

An $n-p-n$ transistor has three leads: the emitter, the base, and the collector. By connecting the base and the collector with moist fingers (which provides a low-resistance path) and observing a large deflection on the ammeter when the positive lead is connected to $A$ and the negative to $C$, we gain insight into the possible configuration of the leads.

The deflection of the ammeter indicates a significant current flow through the transistor. This can happen when:

• The positive terminal of the ammeter is connected to the emitter (which should be more positive).
• The negative terminal is connected to the collector.

This configuration is consistent with how a properly biased $n-p-n$ transistor would operate to allow a large current through the collector-emitter circuit. If $A$ were the emitter and $C$ were the collector, joining the base and collector would allow the transistor to conduct as a result of the biasing.

Assumptions and Explanation:

• A significant deflection of the ammeter suggests that it is connected in series with the main current path of the transistor, which is between the emitter and collector.
• Moist fingers between the base and collector provide sufficient base current to turn the transistor on.
• Therefore, $A, B$, and $C$ are identified as the emitter, base, and collector respectively.

Therefore, the correct interpretation of the leads $A, B$, and $C$ is:

Emitter, base, and collector