Bipolar Junction Transistor MCQ Level -2 - Physics MCQ

A bipolar junction transistor is a three-terminal semiconductor device that consists of two p-n junctions which are able to amplify or magnify a signal. It is a current controlled device. The three terminals of the BJT are the base, the collector, and the emitter. A signal of a small amplitude applied to the base is available in the amplified form at the collector of the transistor. This is the amplification provided by the BJT. Note that it does require an external source of DC power supply to carry out the amplification process.

BJT is a semiconductor device that is constructed with 3 doped semiconductor Regions i.e. Base, Collector & Emitter separated by 2 p-n Junctions.

Bipolar transistors are manufactured in two types, PNP and NPN, and are available as separate components, usually in large quantities. The prime use or function of this type of transistor is to amplify current. This makes them useful as switches or amplifiers. They have a wide application in electronic devices like mobile phones, televisions, radio transmitters, and industrial control.

When one junction is forward biased and either the collector or emitter is open, the BJT will operate in pinch-off region.
The correct answer is: pinch-off region

The common emitter circuit configuration provides voltage gain combined with a moderate current gain, as well as a medium input and a medium output impedance. As such the common emitter configuration is a good all round circuit for use in many applications.

It is also worth noting at this stage that the common emitter transistor amplifier inverts the signal at the input. Therefore if a waveform that is rising enters the input of the common emitter amplifier, it will cause the output voltage to fall. In other words it has a 180° phase change across the circuit.

Dependent upon the actual electronic circuit design itself, the common emitter does not use too many electronic components, sometimes as few as two resistors, although if the bias needs setting for analogue circuits, then four resistors and three capacitors may be used.

In fixed bias, when temperature is increased, the operating point moves toward the saturation region.
The correct answer is: moves towards the saturation region with a decrease in temperature

In an npn transistor, emitter heavily doped, collector is moderately doped and base very thin and least doped, i.e.

The correct answer is:

V_B = 0.7V  (Forward-biased)
and V_BC = -V_CB
= -0.2V (Reverse-biased)
hence, the transistor operates in normal active mode.
The correct answer is: normal active mode

Mica capacitors are preferred for high frequency circuits because they have low ohmic losses and less reactance.

Hence option B is correct

The base of an npn transistor must be positive with respect to emitter. The correct answer is: positive with respect to emitter

If   the BJT will go into the state of saturation.
The correct answer is: 

The region containing the uncomposed acceptor and and donor ions is called depletion region i.e., there is a depletion of mobile charge (holes and free electrons) in this region. Since, this region has immobile ions which are electrically charge, it is also referred to as the space charge region. The electrical field between the acceptor and the donor ions is called a barrier. It is clear that p-side of the junction is negatively charged.
The correct answer is: The p-side of the junction is negatively charged