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:

In an $$n-p-n$$ transistor, connecting the positive lead of the ammeter to terminal A forward-biases the $$p$$-type material, identifying A as the Base. Terminal C is connected directly to the negative lead of the ammeter, while terminal B is only connected indirectly through the resistance of moist fingers. To produce the observed large current deflection, the terminal tied directly to the negative ground must supply a massive amount of charge carriers. Since the Emitter is the most heavily doped region, C must be the Emitter, leaving B as the Collector