Question

The working transistor with its three legs marked P,Q and R is tested using a multimeter. No conduction is found between P & Q. By connecting the common (negative) terminal of the multimeter to R and the other (positive) terminal to P or Q, some resistance is seen on the multimeter. The correct statement for the transistor is
(A) It is a n-p-n transistor with R as base
(B) It is a p-n-p transistor with R as collector
(C) It is a p-n-p transistor with R as emitter
(D) It is a n-p-n transistor with R as collector

Answer 1

Hint: No conduction between P and Q means they both are identical semiconductors. When the negative is connected to R and positive terminal is connected to P or Q, some conduction is obtained, therefore R is p-type semiconductor and acts as base, P and Q are n-type semiconductors.

Complete step by step solution
Firstly, we are given that no conduction is found between the legs P and Q which clearly indicates that both P and Q are the same type of semiconductors, i.e. either both P and Q are n-type or both P and Q are p-type. From here only we can conclude that R has to act as the base here. This indicates option(A) is correct.
Further, when some resistance/conduction is being obtained, the common (negative) terminal of the multimeter is connected to R which means that R is a p-type semiconductor, the other (positive) terminal is connected to either of P or Q which means that they are n-type semiconductors.

Therefore, by double verification, the given transistor is a n-p-n transistor with R as base. Option(A) is correct.

Note For a quick inference, we can say that no conduction is found between P and Q, this means that there has to be some connection between P and R or between Q and R so that R has to act as base. There is only one option in which R is base and that is option(A) so we need not check all the options.