Current Components and Current Gain MCQ Quiz in मल्याळम - Objective Question with Answer for Current Components and Current Gain - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

• In a transistor, small changes in the base current results in large changes in collector current.
• The ratio of change in output current to the change in input current is called the amplification or gain.
• For a.c. input, the gain is denoted by β_ac

Mathematically, we define the AC current gain as:

\(β_{ac}=\frac{\Delta I_o}{\Delta I_{in}}\)

Calculation:

For the given input and output ranges, the current will be:

\(β_{ac}=\frac{(1.5-0.5)\times 10^{-3}}{(40-20)\times 10^{-6}}\)

β_ac = 50

The Correct answer is option (3)

Concept:

Common Emitter (CE) Configuration of Transistor:

• In the Common Emitter or grounded emitter configuration, the input signal is applied between the base and the emitter
• While the output is taken from between the collector and the emitter.
• This type of configuration is the most commonly used circuit for transistor-based amplifiers and which represents the “normal” method of bipolar transistor connection.
• The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations.
• This is mainly because the input impedance is LOW as it is connected to a forward biased PN-junction.
• while the output impedance is HIGH as it is taken from a reverse-biased PN-junction.

• In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as I_E = I_C + I_B.

Fig: CE configuration of transistor

• As the emitter current for a common emitter configuration is defined as I_E = I_C + I_B,
• The ratio of I_C / I_E is called Alpha, given the Greek symbol of α.
• The value of alpha is always less than unity.
• Since the electrical relationship between these three currents, I_B, I_C and I_E is determined by the physical construction of the transistor itself, any small change in the base current ( IB ), will result in a much larger change in the collector current ( I_C ).
• By combining the expressions for both Alpha (α) and Beta (β) the mathematical relationship between these parameters and therefore the current gain of the transistor can be given as:

\(α = \frac{I_C}{I_E}\)

and \(β = \frac{I_C}{I_B}\)

∴ \(I_C = α I_E= β I_B\)

as: \(α = \frac{β }{β +1 }\)

and \(β = \frac{α }{1-α }\ \)

I_E = I_C + I_B

Where I_E = Emitter Current

I_C = Collector Current

I_B = Base Current

α = Current Gain in the common-base circuit of transistor

β = Current gain in the common-emitter circuit

Common emitter transistor configuration:

• This transistor configuration is probably the most widely used.
• The circuit provides medium input and output impedance levels.
• Both current and voltage gain can be described as medium, but the output is the inverse of the input, i.e. 180° phase change.
• This provides good overall performance as well as efficiency.
• It is often the most widely used configuration.
   

Additional Information The various characteristics of different configurations are shown,

Concept:

Common base current gain (α) is defined as the ratio of collector current to emitter current of a transistor.

\(α = \dfrac{{{I_c}}}{{{I_e}}}\)

\(α = \dfrac{β }{{β + 1}}\)

Common emitter current gain (β) is defined as the ratio of collector current to base current transistor.

\(β = \dfrac{{{I_c}}}{{{I_b}}}\)

\(β = \dfrac{α }{{1 - α }}\)

Calculation:

Given- β = 99

\(\therefore α = \dfrac{{{I_c}}}{{{I_e}}} = \dfrac{{99}}{{ 99+1}}\)

α = 0.99

Concept:

• ​The doping concentration at the base affects the emitter gain (β), i.e. β is dependent on the doping concentration.
• If the doping at the base increases, the recombination of the carriers from the emitter region increases. This reduces the emitter current gain, as fewer carriers from the emitter finally reach the collector.
• Similarly, less the doping concentration at the base, less will be the recombination of the carriers at the base and more carriers will reach the collector resulting in more emitter gain.

Mathematically this can be written as:

\(\beta \propto\frac{1}{Base~Doping}\)

Analysis:

For transistor T1, we can write:

\(\beta \propto\frac{1}{N_{B1}}\)   ---(1)

For transistor T2, we can write:

\(\beta_2\propto\frac{1}{N_{B2}}\)   ---(2)

Dividing both the equations, we get:

\(\frac{\beta_1}{\beta_2}=\frac{N_{B2}}{N_{B1}}\)   ---(3)

NB = Net concentration at the base also called the dose.

\(N_B=∫(Doping~ Concentration)dx\)

Calculation:

For transistor T1, we get:

\({N_{B1}} = \mathop \smallint \limits_0^W {N_{B1}}\left( x \right)dx\)

From the given doping profile, we get:

\({N_{B1}}\left( x \right) = \left( {\frac{{{{10}^{17}} - {{10}^{14}}}}{{0 - W}}} \right)x + {N_{B1}}\left( 0 \right)\)

\({N_{B1}}\left( x \right) \approx \left( { - \frac{{{{10}^{17}}}}{W}} \right)x + {10^{17}}\)

The net concentration or dose at the base of transistor T2 will be:

\({N_{B2}} = \mathop \smallint \nolimits \left( {\left( { - \frac{{{{10}^{17}}}}{W}} \right)x + {{10}^{17}}} \right)dx\)

\({N_{B2}} = \mathop \smallint \nolimits \left( {\left( { - \frac{{{{10}^{17}}}}{W}} \right)\left( {\frac{{{x^2}}}{2}} \right) + {{10}^{17}}x} \right)_0^W\)

\({N_{B2}} = \left( { - \frac{{{{10}^{17}}}}{W}} \right)\left( {\frac{{{W^2}}}{2}} \right) + {10^{17}}W\)

\({N_{B2}} = {10^{17}}W - \frac{{{{10}^{17}}}}{2}W\)

\({N_{B2}} = \frac{{{{10}^{17}}}}{2}W\)

The ratio of the two emitter gains, using Equation (3) will be:

\(\frac{{{\beta _1}}}{{{\beta _2}}} = \frac{{{{10}^{17}}W}}{{\frac{{{{10}^{17}}W}}{2}}}\)

\(\frac{{{\beta _1}}}{{{\beta _2}}} = 2\)

β1 = 2 β2

Concept:

ICEO is the reverse leakage current in the common-emitter configuration of BJT when the base is open.

ICBO is the reverse leakage current in the common-base configuration of BJT when the emitter is open.

Also, ICEO > ICBO

And they are related by the relation:

ICEO = (1 + β) ICBO

Total collector current is given by:

IC = βIB + ICBO(β + 1) ---(1)

Application:

Given I_c = 4 mA, I_B = 50 μA, α = 0.98

∴ \(β = \dfrac{\alpha}{1 - \alpha} = 49\)

From equation (1)

4 × 10^-3 = 50 × 10^-6 × 49 + (50) I_CBO

\(\dfrac{4}{50} × 10^{-3} = 49 × 10^{-6} + I_{CBO}\)

I_CBO = (80 × 10^-6) - (49 × 10^-6)

= 31 × 10^-6 A = 31 μA

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 correct answer is the Chemical effect of electric current.

Key Points

• When current is passed through a conducting solution, bubbles of gas are formed on the electrodes. This shows the Chemical effect of electric current.
• This experiment was shown by British Chemist William Nicholson in the year 1800.
• The chemical reaction takes place when an electric current is passed through a conducting solution and this results in the formation of bubbles of gas on the electrodes.
• Deposits of metal may be seen on electrodes and sometimes colour changes in solutions may occur.
• This reaction totally depends upon what solution and electrodes are used and also some chemical effects of the electric current may occur.

The various characteristics of different configurations are shown 

From the table, it is clear that the current gain is lowest in the common base amplifier and Highest in the Common collector amplifier

Concept:

For a transistor, the base current, the emitter current, and the collector current are related as:

IE = IB + IC

where IC = βdc IB

βdc = Current gain of the transistor

Calculation:

Given IB = 20 μA and βdc = 60.

The collector current will be:

IC = 60 × 20 μA

IC = 1200 μA

Note: In milliAmpere, we get:

IC = 1200 × 10-6 A

IC = 1.2 × 10-3 A

IC = 1.2 mA