# 41 Lecture

## Directions of Currents in BJT

In circuit theory, bipolar junction transistor (BJT) is a widely used device for amplifying or switching electrical signals. Understanding the directions of currents in a BJT is crucial for its proper operation and design.

## Important Mcq's Midterm & Finalterm Prepration Past papers included

In which direction does the majority carrier flow in an NPN transistor?

a) From the base to the emitter

b) From the emitter to the base

c) From the collector to the base

d) From the base to the collector

Answer: b) From the emitter to the base

In which direction does the minority carrier flow in an NPN transistor?

a) From the base to the emitter

b) From the emitter to the base

c) From the collector to the base

d) From the base to the collector

Answer: a) From the base to the emitter

In which direction does the majority carrier flow in a PNP transistor?

a) From the base to the emitter

b) From the emitter to the base

c) From the collector to the base

d) From the base to the collector

Answer: a) From the base to the emitter

In which direction does the minority carrier flow in a PNP transistor?

a) From the base to the emitter

b) From the emitter to the base

c) From the collector to the base

d) From the base to the collector

Answer: b) From the emitter to the base

In an NPN transistor, the direction of the base current is _____ the direction of the emitter current.

a) opposite to

b) same as

c) perpendicular to

d) unrelated to

In a PNP transistor, the direction of the base current is _____ the direction of the emitter current.

a) opposite to

b) same as

c) perpendicular to

d) unrelated to

In an NPN transistor, the direction of the collector current is _____ the direction of the emitter current.

a) opposite to

b) same as

c) perpendicular to

d) unrelated to

In a PNP transistor, the direction of the collector current is _____ the direction of the emitter current.

a) opposite to

b) same as

c) perpendicular to

d) unrelated to

In which region of operation of a BJT does the collector current depend on the base current?

a) Cut-off region

b) Active region

c) Saturation region

d) None of the above

In which region of operation of a BJT does the collector current saturate?

a) Cut-off region

b) Active region

c) Saturation region

d) None of the above

## Subjective Short Notes Midterm & Finalterm Prepration Past papers included

What is the direction of base current in an NPN BJT?

Answer: The direction of base current in an NPN BJT is from the emitter to the base.

What is the direction of collector current in an NPN BJT?

Answer: The direction of collector current in an NPN BJT is from the collector to the emitter.

What is the direction of emitter current in an NPN BJT?

Answer: The direction of emitter current in an NPN BJT is from the emitter to the collector.

What is the direction of base current in a PNP BJT?

Answer: The direction of base current in a PNP BJT is from the base to the emitter.

What is the direction of collector current in a PNP BJT?

Answer: The direction of collector current in a PNP BJT is from the emitter to the collector.

What is the direction of emitter current in a PNP BJT?

Answer: The direction of emitter current in a PNP BJT is from the collector to the emitter.

What is the significance of the direction of base current in an NPN BJT?

Answer: The direction of base current in an NPN BJT determines the amount of collector current that flows through the device.

Why is the direction of emitter current in an NPN BJT opposite to that of a PNP BJT?

Answer: The direction of emitter current in an NPN BJT is opposite to that of a PNP BJT because the majority carriers in the emitter region of an NPN BJT are electrons, while in a PNP BJT, they are holes.

What is the significance of the direction of collector current in a PNP BJT?

Answer: The direction of collector current in a PNP BJT determines the amount of emitter current that flows through the device.

Why is the direction of base current in a PNP BJT opposite to that of an NPN BJT?

Answer: The direction of base current in a PNP BJT is opposite to that of an NPN BJT because the PNP BJT is a minority carrier device, which means that it operates with holes as the majority carrier in the base region, unlike an NPN BJT which operates with electrons as the majority carrier.

Directions of Currents in BJT In circuit theory, bipolar junction transistor (BJT) is a widely used device for amplifying or switching electrical signals. Understanding the directions of currents in a BJT is crucial for its proper operation and design. In this article, we will discuss the directions of currents in a BJT and their significance in circuit analysis. A BJT consists of three doped regions, namely the emitter, base, and collector, connected to two pn junctions. The emitter region is heavily doped and has a large number of free electrons, while the base region is lightly doped and has a small number of holes. The collector region is moderately doped and has a small number of free electrons. When a voltage is applied across the emitter-base junction, it forward biases the junction and allows the current to flow from the emitter to the base. Similarly, when a voltage is applied across the collector-base junction, it reverse biases the junction and allows only a small current to flow from the collector to the base. To understand the directions of currents in a BJT, we consider its common emitter configuration, which is the most widely used configuration in amplifier circuits. In this configuration, the emitter is connected to the ground, the input signal is applied to the base, and the output signal is taken from the collector. The direction of currents in the BJT is defined with respect to this configuration. The direction of emitter current (Ie) is from the emitter towards the base, and the direction of collector current (Ic) is from the collector towards the base. The direction of base current (Ib) is from the base towards the emitter. These directions are consistent with the flow of majority carriers in the various regions of the BJT. The significance of the directions of currents in a BJT can be understood in terms of the BJT equations, which relate the various currents and voltages in the device. The BJT equations are given by: Ie = Ib + Ic (1) Ic = ?Ib (2) where ? is the current gain of the transistor. Equation (1) represents the law of conservation of charge, which states that the total current flowing into a region must be equal to the total current flowing out of that region. Equation (2) represents the amplification property of the transistor, which states that the collector current is proportional to the base current with a proportionality factor ?. The directions of currents in a BJT are also important for determining the biasing conditions of the transistor. Biasing is the process of applying a DC voltage to the transistor terminals to ensure its proper operation in a circuit. The biasing conditions depend on the type of BJT and the desired operating point. For example, in an NPN transistor, the base-emitter junction is forward biased, and the collector-base junction is reverse biased for proper operation. In contrast, for a PNP transistor, the base-emitter junction is reverse biased, and the collector-base junction is forward biased. In conclusion, the directions of currents in a BJT are crucial for its proper operation and design in circuit analysis. The emitter current flows from the emitter towards the base, the collector current flows from the collector towards the base, and the base current flows from the base towards the emitter. The directions of currents are consistent with the flow of majority carriers in the various regions of the transistor. The BJT equations relate the various currents and voltages in the device and represent the amplification and conservation properties of the transistor. The biasing conditions of the transistor depend on the type of BJT and the desired operating point.