Common Base Current Gain MCQ Quiz - Objective Question with Answer for Common Base Current Gain - Download Free PDF

In a transistor, the phase shift of the output signal relative to the input signal depends on the transistor configuration:

• Common Emitter (CE) configuration: In this configuration, the output signal is inverted, meaning it is phase-shifted by 180°.
• Common Base (CB) configuration: The output signal has no phase shift relative to the input signal.
• Common Collector (CC) configuration: The output signal has no phase shift and is in phase with the input signal.

Given that the output signal is phase-shifted by 180°, this is characteristic of the Common Emitter (CE) configuration of a transistor.

∴ The transistor configuration is Option 2) Common Emitter (CE).

Concept of Current Amplification Factor in Common Base Connection:

In a common base connection of a transistor, the ratio of the change in the output current (collector current, I_C) to the change in the input current (emitter current, I_E) at a constant collector-base voltage (V_CB) is called the current amplification factor. This factor is denoted by α (alpha).

The current amplification factor (α) is given by:

α = ΔI_C / ΔI_E

Where,

• ΔI_C = Change in collector current
• ΔI_E = Change in emitter current

Given Options:

1. Output resistance factor
2. Current amplification factor
3. Base current amplification factor
4. Input resistance factor
    

Conclusion:

The correct term for the ratio of the change in the output current to the change in the input current at a constant collector-base voltage in a common base connection is: Current amplification factor

Input Terminal Emitter–Base (EB)

Output Terminal Collector–Base (CB)

Input voltage: VEB

Output current: IC

Since for Amplification Application in BJT

EB Junction → Forward Biased (Low Impedance)

CB Junction → Reversed Biased (High Impedance)

Comparison:

The common-emitter current gain (β) is the ratio of the transistor's collector current to the transistor's base current, i.e.

\(β = \frac{{{I_C}}}{{{I_B}}}\)

And the common base DC current gain (α) is a ratio of the transistor's collector current to the transistor's emitter current, i.e.

\(α = \frac{{{I_C}}}{{{I_E}}}\)

The transistor currents are related by the relation:

IE = IB + IC

α can now be written as:

\(α = \frac{{{I_C}}}{{{I_B+I_C}}}\)

Dividing both the numerator and denominator by IB, we get:

\(α = \frac{{{I_C/I_B}}}{{{1+I_C/I_B}}}\)

Since \(β = \frac{{{I_C}}}{{{I_B}}}\)

\(α = \frac{β }{{β + 1}}\) 'or' .... (1)

\(β = \frac{α }{{1-α}}\) .... (2)

Now, from equations (1),

\(1-α = 1-\frac{β }{{β + 1}}\)

or, \(1-α = \frac{(1+\beta)-\beta }{{β + 1}}\)

Hence, \(1-\alpha = \frac{1}{1 +\beta}\)

Current amplification factor: It is defined as the ratio of the output current to the input current. In the common-base configuration, the output current is emitter current IC, whereas the input current is base current IE.

Thus, the ratio of change in collector current to the change in the emitter current is known as the current amplification factor. It is expressed by the α.

\(\alpha = \frac{{{\rm{\Delta }}{I_C}}}{{{\rm{\Delta }}{I_E}}}\)

Where, I_E = I_C + I_B

Calculation:

Given,

I_E = 2 mA

I_B = 20 μA = 0.02 mA

From above concept,

I_C = 2 mA - 0.02 mA = 1.98 mA

Current amplification factor is given as,

\(\alpha=\frac{I_C}{I_E}=\frac{1.98}{2}=0.99\)

Current amplification factor: It is defined as the ratio of the output current to the input current. In the common-base configuration, the output current is emitter current IC, whereas the input current is base current IE.

Thus, the ratio of change in collector current to the change in the emitter current is known as the current amplification factor. It is expressed by the α.

\(\alpha = \frac{{{\rm{\Delta }}{I_C}}}{{{\rm{\Delta }}{I_E}}}\)

Where, I_E = I_C + I_B

Calculation:

Given,

I_E = 2 mA

I_B = 20 μA = 0.02 mA

From above concept,

I_C = 2 mA - 0.02 mA = 1.98 mA

Current amplification factor is given as,

\(\alpha=\frac{I_C}{I_E}=\frac{1.98}{2}=0.99\)

Concept of Current Amplification Factor in Common Base Connection:

In a common base connection of a transistor, the ratio of the change in the output current (collector current, I_C) to the change in the input current (emitter current, I_E) at a constant collector-base voltage (V_CB) is called the current amplification factor. This factor is denoted by α (alpha).

The current amplification factor (α) is given by:

α = ΔI_C / ΔI_E

Where,

• ΔI_C = Change in collector current
• ΔI_E = Change in emitter current

Given Options:

1. Output resistance factor
2. Current amplification factor
3. Base current amplification factor
4. Input resistance factor
    

Conclusion:

The correct term for the ratio of the change in the output current to the change in the input current at a constant collector-base voltage in a common base connection is: Current amplification factor

Input Terminal Emitter–Base (EB)

Output Terminal Collector–Base (CB)

Input voltage: VEB

Output current: IC

Since for Amplification Application in BJT

EB Junction → Forward Biased (Low Impedance)

CB Junction → Reversed Biased (High Impedance)

Comparison:

Current amplification factor: It is defined as the ratio of the output current to the input current. In the common-base configuration, the output current is emitter current IC, whereas the input current is base current IE.

Thus, the ratio of change in collector current to the change in the emitter current is known as the current amplification factor. It is expressed by the α.

\(\alpha = \frac{{{\rm{\Delta }}{I_C}}}{{{\rm{\Delta }}{I_E}}}\)

Where, I_E = I_C + I_B

Calculation:

Given,

I_E = 2 mA

I_B = 20 μA = 0.02 mA

From above concept,

I_C = 2 mA - 0.02 mA = 1.98 mA

Current amplification factor is given as,

\(\alpha=\frac{I_C}{I_E}=\frac{1.98}{2}=0.99\)

Concept of Current Amplification Factor in Common Base Connection:

In a common base connection of a transistor, the ratio of the change in the output current (collector current, I_C) to the change in the input current (emitter current, I_E) at a constant collector-base voltage (V_CB) is called the current amplification factor. This factor is denoted by α (alpha).

The current amplification factor (α) is given by:

α = ΔI_C / ΔI_E

Where,

• ΔI_C = Change in collector current
• ΔI_E = Change in emitter current

Given Options:

1. Output resistance factor
2. Current amplification factor
3. Base current amplification factor
4. Input resistance factor
    

Conclusion:

The correct term for the ratio of the change in the output current to the change in the input current at a constant collector-base voltage in a common base connection is: Current amplification factor

The common base current gain is denoted by α

Common emitter current gain is β

Common collector current gain is γ

The relation between α and β is

\(\beta = \frac{\alpha }{{1 - \alpha }}\)

i.e.

\(\beta = \frac{{0.9}}{{1 - 0.9}} = \frac{{0.9}}{{0.1}} = 9\)

γ = 1 + β

Concept:

\(\beta = \frac{\alpha }{{1 - \alpha }}\)

Where,

β = common-emitter current gain

α = Common base current gain

Calculation:

Common base current gain = α = 0.95

\(\beta = \frac{{0.95}}{{1 - 0.95}} = 19\)

Note: 

\(\alpha = \frac{{{I_C}}}{{{I_E}}}\) & \(\beta = \frac{{{I_C}}}{{{I_B}}}\)

Where IC = Collector current

IE = Emitter current

IB = Base current

The DC current gain of a common collector is therefore given by the ratio of emitter current to the base current, i.e.

\(\gamma=\frac{I_E}{I_B}\)

IE = Emitter Current

IB = Base Current

Also, IE = IB + IC

DC current gain will be:

\(\gamma=\frac{I_C+I_B}{I_B}=\frac{I_C}{I_B}+1\)

The DC current gain for a common emitter configuration is defined as:

\(\beta=\frac{I_C}{I_B}\)

Equation (1) now becomes:

\(\gamma=\beta +1\)

Important Differences between different transistor configuration is as shown:

Concept: 

The common base DC current gain (α) is a ratio of the transistor's collector current (IC) to the transistor's emitter current (IE), i.e.

\(\alpha = \frac{{{I_c}}}{{{I_E}}}\)

And the common-emitter current gain (β) is the ratio of the transistor's collector current (IC) to the transistor's base current (IB), i.e.

\(\beta = \frac{{{I_C}}}{{{I_B}}}\)

Derivation:

The transistor currents are related by the relation:

I_E = I_B + I_C

α can now be written as:

\(α = \frac{{{I_C}}}{{{I_B+I_C}}}\)

Dividing both the numerator and denominator by IB, we get:

\(α = \frac{{{I_C/I_B}}}{{{1+I_C/I_B}}}\)

Since \(β = \frac{{{I_C}}}{{{I_B}}}\)

\(α = \frac{β }{{β + 1}}\) 'or'

\(β = \frac{α }{{1-α}}\)

Important Differences between different transistor configuration is as shown:

Input Terminal Emitter–Base (EB)

Output Terminal Collector–Base (CB)

Input voltage: VEB

Output current: IC

Since for Amplification Application in BJT

EB Junction → Forward Biased (Low Impedance)

CB Junction → Reversed Biased (High Impedance)

Comparison: