Question

Transistor is a
(A) Current-controlled current device
(B) Current-controlled voltage device
(C) Voltage-controlled current device
(D) Voltage-controlled voltage device

Answer 1

Hint : Take the case of a bipolar junction transistor that uses two types of charge carriers to function. A bipolar junction transistor is an electronic device that amplifies the current that flows through the base-emitter current into the collector-emitter current with the amplification factor being beta which is defined as the ratio of the collector current to the base current.

Complete step by step answer
A transistor is a semiconductor used to amplify electronic signals or switch electronic signals. The bipolar junction transistor is one of the most commonly used transistors. A transistor has three parts: emitter, base, and collector. A transistor contains two semiconductor types namely n-type and p-type. Together they either form an NPN type transistor or a PNP type transistor. In a bipolar junction transistor, the collector current is due to the flow of electrons or holes that comes from the highly doped emitter part of the transistor, that passes the base part where these carriers are lightly doped, that then diffuses to the collector part of the transistor. The ratio of the output current to the input current is defined as the current amplification factor. It is given by the ratio of the collector current to the base current.
$\Rightarrow \beta =\dfrac{{{I}_{c}}}{{{I}_{b}}}$
The output current is dependent on the input currents, or the collector current is controlled by the base current. So, a bipolar junction transistor is a current controlled device. The output characteristics of a bipolar junction transistor are dependent on the base current.
The voltage across a base-emitter junction is set so that the electric field due to this external voltage will reduce the width of the depletion region. This electric field determines the flow of the charge carriers in a transistor.
So, we can conclude that a transistor is a current-controlled voltage device.
Hence, option (B) is the correct answer.

Note
In this question, we have assumed that the transistor under consideration to be a bipolar junction transistor. So, it is a current-controlled electronic device. If we have taken a field-effect transistor or FET transistor the function would change as it is a voltage-controlled device.