Given below are two statements :
Statement I : PN junction diodes can be used to function as transistor, simply by connecting two diodes, back to back, which acts as the base terminal.
Statement II : In the study of transistor, the amplification factor β indicates ratio of the collector current to the base current.
In the light of the above statements, choose the correct answer from the options given below.

Solution

Physics sir · 3 steps

A transistor is not two diodes glued together: its base must be thin and lightly doped, all in one crystal.

1. Statement I. In a transistor, carriers from the emitter must cross the base and reach the collector. That only works because the base is very thin and lightly doped, so almost no carriers recombine there. Two separate diodes joined back to back make a thick base region plus a metal wire, so the carriers recombine before reaching the collector. There is no transistor action, so Statement I is false.
2. Statement II. The current amplification factor β of a transistor, in common-emitter mode, compares the output collector current with the input base current. That is exactly what the statement says, so Statement II is true.

   β = I_C/I_B

3. So. Statement I is false and Statement II is true, which is option (b).

The idea to keep. Transistor action needs a thin, lightly doped base shared inside one crystal, so two diodes back to back never behave like a transistor. Remember β = I_C/I_B and α = I_C/I_E.

Answer from the NTA final answer key. Solution by PrepWiser.