Question

A transistor is essentially
(A) A current operated device
(B) Power driven device
(C) A voltage operated device
(D) Resistance operated device

Answer 1

Hint: To answer this question, we need to consider the active mode operation of the bipolar junction transistor. The parameter which controls the output of the transistor will be the answer to this question.

Complete answer:
We know that a bipolar junction transistor consists of three terminals, known as the emitter, the base and the collector. A transistor is of two types; one is the n-p-n transistor and the other one is the p-n-p transistor. In the n-p-n transistor, the emitter and the collector are the n-type semiconductors, while the base is p-type. But in the p-n-p transistor, the emitter and the collector are p-type, while the base is n-type. Now, a transistor is generally operated in the active mode, in which the emitter base junction is forward biased, while the base collector junction is reversed biased. So let us take the example of the transistor working in active mode operation.
The emitter is known as the input terminal, while the collector is known as the output terminal.
Since the collector base junction is reversed biased, so the current is constituted by the minority charge carriers. The electrons from the base flow into the collector, while the holes flow from the collector to the base terminal. Since the minority charge carriers are very less, so the current becomes saturated for a particular value of the reverse voltage. Now, since the emitter base junction is forward biased, so the electrons from the emitter flow into the base, increasing the minority charge carriers in the base. This eventually results in higher value of the saturation current at the output.
Now, as can be appreciated from the above, the output of a transistor is controlled by the current at the input. The output is not voltage controlled, since the output current becomes saturated and does not increase even after increasing the voltage.
Thus, a bipolar junction transistor is essentially a current operated device.
Hence, the correct answer is option (A).

Note:
We must note that not all the transistors are current operated devices. Only the bipolar junction transistor is currently operated. The other type of transistor, for example, is the field effect transistor which is voltage operated.