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Bipolar Junction Transistor - Class XII

Comprehensive coverage of BJT characteristics including current gain (α, β), voltage gain, power gain, common emitter and common base configurations, and transistor amplifier parameters

34 Questions Published
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Questions

Question 1 Multiple Choice (Single Answer)

The input resistance of a silicon transistor is $1 k\Omega $.If base current is changed by $100 \mu A$ it causes the change in collector current by $2 mA$. This transistor is used as a CE amplifier with a load resistance of $5 k\Omega$ What is the ac voltage gain of amplifier?

  1. $10$
  2. 44100$
  3. $500$
  4. $200$
Question 2 Multiple Choice (Single Answer)

In a silicon transistor the base current is changed by $25\mu A$. This results in a change of $0.04\ V$ in the base to emitter voltage and a change of $4\ mA$ in the collector current. The trans-conductance of the transistor (in $\Omega^{-1}$) is

  1. $0.1$
  2. $1$
  3. $1000$
  4. $0.01$
Question 3 Multiple Choice (Multiple Answers)

For a common emitter configuration, If $\alpha $and $\beta $ have thier usual meanings. The incorrect relationship between $\alpha $and $\beta $ is:

  1. $\alpha =\dfrac { \beta }{ 1-\beta } $
  2. $\alpha =\dfrac { \beta }{ 1+\beta } $
  3. $\alpha =\dfrac { { \beta }^{ 2 } }{ 1+{ \beta }^{ 2 } } $
  4. $\dfrac { 1 }{ \alpha } =\dfrac { 1 }{ \beta } +1$
Question 4 Multiple Choice (Single Answer)

For a common emitter connection the values of constant collector current and base current are $5\ mA$ and $50$$\mu A$ respectively. The current gain will be

  1. $10$
  2. $20$
  3. $40$
  4. $100$
Question 5 Multiple Choice (Single Answer)

In a silicon transistor, the base  current is changed by 20 change of 0.02V in base to emitter voltage and a change of 2mA in the collector current.
(a) Find the input  resistance ${ \beta  } _{ ac }$ 
(b) If this transistor is used as an-amplifier. Find the voltage gain of the-amplifier with the load resistance 5k amplifier.

  1. a)100b)-500
  2. a)1000b)-500
  3. a)2000b)-5000
  4. a)10b)-5
Question 6 Multiple Choice (Single Answer)

The ac current gain of a transistor is $120$. What is the change in the collector current in the transistor whose base current changes by $100\ \mu A$?

  1. $6\ mA$
  2. $12\ mA$
  3. $3\ mA$
  4. $24\ mA$
Question 7 Multiple Choice (Single Answer)

Current gain of a transistor is $0.99$. If it is used in common emitted mode to form a transistor amplifier with input resistance $1\ k\Omega$ and load resistance $10\ k\Omega$, then the voltage gain of the amplifier is

  1. $99$
  2. $0.99$
  3. $9.9$
  4. $990$
Question 8 Multiple Choice (Single Answer)

For a CE transistor amplifier, the audio signal voltage across the collector resistance of $2k\Omega $ is 2 V.Suppose the current amplification factor of the transistor is 100. The value of ${R _B}$ in series with ${V _{BB}}$ the supply of 2V, if the DC base current has to be 10 times the signal current is 

  1. $4k\Omega $
  2. $14k\Omega $
  3. $28k\Omega $
  4. $54k\Omega $
Question 9 Multiple Choice (Single Answer)

When a collector to emitter voltage is constant in a transistor, the collector current changes by $8.2mA$ when the emitter current changes by $8.3mA$. The value of forward current ratio $B$ is

  1. $82$
  2. $83$
  3. $8.2$
  4. $8.3$
Question 10 Multiple Choice (Single Answer)

In the CB mode of a transistor when the collector voltage is changed by $0.5V$. The collector current changes by $0.05mA$. The output resistance will be

  1. $10k\Omega$
  2. $20k\Omega$
  3. $5k\Omega$
  4. $2.5k\Omega$
Question 11 Multiple Choice (Single Answer)

Consider an n-p-n transistor amplifier in common-emitter configuration. The current gain of the transistor is $100$. if the collector current changes by $1mA$. What will be the change in emitter current.

  1. $1.1mA$
  2. $1.01mA$
  3. $0.01mA$
  4. $10mA$
Question 12 Multiple Choice (Single Answer)

Power gain for $N - P - N$ transistor is $10^6$, input resistance $100 \Omega$ and output resistance $1000 ,\Omega$. find out current gain.

  1. $100$
  2. $150$
  3. $200$
  4. $50$
Question 13 Multiple Choice (Single Answer)

A transistor, when connected in common emitter mode, has a:

  1. high input resistance and a low output resistance
  2. medium input resistance and high output resistance
  3. very low input resistance and a low output resistance
  4. high input resistance and a high output resistance
Question 14 Multiple Choice (Single Answer)

What is the voltage gain in a common emitter amplifier, where input resistance is $3.2$ and load resistance $24$$\Omega, \beta$$ = 0.6$?

  1. $8.4$
  2. $4.8$
  3. $2.4$
  4. $480$
Question 15 Multiple Choice (Single Answer)

In a common emitter transistor amplifier $\beta$ $= 60$, $R _0$ $= 5000$$\Omega$ and internal resistance of a transistor is $500$$\Omega$. The voltage amplification of amplifier will be

  1. $500$
  2. $460$
  3. $600$
  4. $560$
Question 16 Multiple Choice (Single Answer)

In common emitter amplifier, the current gain is $62$.The collector resistance and input resistance are $5\ k$$\Omega$ an $500$ $\Omega$ respectively. If the input voltage is $0.01\ V$, the output voltage is

  1. $0.62\ V$
  2. $6.2\ V$
  3. $62\ V$
  4. $620\ V$
Question 17 Multiple Choice (Single Answer)

The current gain $\beta$-may be defined as

  1. the ratio of change in collector current to the change in emitter current for a constant collector voltage in a common base arrangement
  2. the ratio of change in collector current to the change in base current at constant collector voltage in a common emitter circuit
  3. the ratio of change in emitter current to the change in base current for constant emitter voltage in common emitter circuit
  4. the ratio of change in base current to the change in collector current in constant collector voltage in common emitter circuit
Question 18 Multiple Choice (Single Answer)

A transistor based radio receiver set $($effective resistance of the order of $18$ $ohms$$)$ operates on a $9V$ dc battery. If this replaced by a dc power supply with rating $9V$, $500V$ then

  1. Receiver will work normally
  2. Receiver will give distorted output
  3. Receiver will get burnt
  4. Power supply will get over heated
Question 19 Multiple Choice (Single Answer)

The current gain for a transistor working as common base amplifier is $0.96$. lf the emitter current is $7.2 mA$, the base current will be :

  1. $0.42 mA$
  2. $0.49 mA$
  3. $0.29 mA$
  4. $0.35 mA$
Question 20 Multiple Choice (Single Answer)

For a common emitter circuit if $I _C$ / $I _E$ =0.98 then current gain for common emitter circuit will be

  1. 4.9
  2. 98
  3. 49
  4. 9.8
Question 21 Multiple Choice (Single Answer)

In a p-n-p transistor, working as a common base amplifier, current gain is 0.96 and emitter current is 7.2mA. The base current is

  1. 0.20 mA
  2. 0.36 mA
  3. 0.29 mA
  4. 0.45 mA
Question 22 Multiple Choice (Single Answer)

A transistor is operated in common emitter configuration at $V _c=2V$ such that a change in the base current from $100\mu A$ to $300\mu A$ produces a change in the collector current from 10mA to 20mA. The current gain is

  1. $50$
  2. $75$
  3. $100$
  4. $25$
Question 23 Multiple Choice (Single Answer)

For a transistor amplifier in common emitter configuration for load impedance of 1 k ( $h _{fe}$ = 50 and $h _{oe}$ = $25 \times 10^{-6}$) the current gain is

  1. -48.78
  2. -15.7
  3. -24.8
  4. -5.2
Question 24 Multiple Choice (Single Answer)

The voltage gain of an amplifier with 9 negative feedback is 10. The voltage gain without feedback will be

  1. 90
  2. 100
  3. 10
  4. 1.25
Question 25 Multiple Choice (Single Answer)

The input resistance of a common emitter amplifier is $330 \Omega$ and the load resistance is $5 k \Omega$. A change of base current is $15 \mu A$ results in the change of collector current by $1 mA$. The voltage gain of amplifier is

  1. $1000$
  2. $10001$
  3. $1010$
  4. $1100$
Question 26 Multiple Choice (Single Answer)

The relationship between current gain $\alpha$ in Common Base [CB] mode and current gain $\beta$ in Common Emitter [CE] mode is

  1. $\beta = \alpha + 1$
  2. $\beta = \dfrac{\alpha}{1 - \alpha}$
  3. $\beta = \dfrac{\alpha}{1 + \alpha}$
  4. $\beta = 1 - \alpha$
Question 27 Multiple Choice (Single Answer)

In a common base transistor circuit, $I _C$ is the output current and $I _E$ is the input current. The current gain a pc is 

  1. Equal to one
  2. Greater than one
  3. Less than one
  4. None of these
Question 28 Multiple Choice (Single Answer)

For a transistor in common base, the current gain is $0.95$. If the load resistance is $400\ k\Omega$ and input resistance is $200\Omega$, then the voltage gain and power gain will be

  1. $1900$ and $1800$
  2. $1900$ and $1805$
  3. $5525$ and $3591$
  4. $1805$ and $1900$
Question 29 Multiple Choice (Single Answer)

In a transistor amplifier, the two a.c. current gains $\alpha$ and $\beta$ are defined as $\alpha =\delta I _{C}/ \delta I _{E}$ and $\beta = \delta I _{C}/ \delta I _{B}$.
The relation between $\alpha$ and $\beta$ is

  1. $\beta = \dfrac {1 + \alpha}{\alpha}$
  2. $\beta = \dfrac {1 - \alpha}{\alpha}$
  3. $\beta = \dfrac {\alpha}{1 - \alpha}$
  4. $\beta = \dfrac {\alpha}{1 + \alpha}$
Question 30 Multiple Choice (Single Answer)

In CE NPN transistor ${10}^{10}$ electrons enter the emitter in ${10}^{-6}$s when it is connected to battery. About $5$% electrons recombine with holes in the base. The current gain of the transistor is______
$\left( e=1.6\times { 10 }^{ -19 }C \right) $

  1. $0.98$
  2. $19$
  3. $49$
  4. $0.95$
Question 31 Multiple Choice (Single Answer)

In a common emitter configuration with suitable bias, it is given than ${R} _{L}$ is the load resistance and ${R} _{BE}$ is small signal dynamic resistance (input side). Then, voltage gain, current gain and power gain are given, respectively, by:
$\beta$ is current gain, ${ I } _{ B },{ I } _{ C },{ I } _{ E }$ are respectively base, collector and emitter currents:

  1. $\beta \cfrac { { R } _{ L } }{ { R } _{ BE } } ,\cfrac { \Delta { I } _{ E } }{ \Delta { I } _{ B } } ,{ \beta }^{ 2 }\cfrac { { R } _{ L } }{ { R } _{ BE } } $
  2. ${ \beta }^{ 2 }\cfrac { { R } _{ L } }{ { R } _{ BE } } ,\cfrac { \Delta { I } _{ C } }{ \Delta { I } _{ B } } ,\beta \cfrac { { R } _{ L } }{ { R } _{ BE } } $
  3. ${ \beta }^{ 2 }\cfrac { { R } _{ L } }{ { R } _{ BE } } ,\cfrac { \Delta { I } _{ C } }{ \Delta { I } _{ E } } ,{ \beta }^{ 2 }\cfrac { { R } _{ L } }{ { R } _{ BE } } $
  4. $\beta \cfrac { { R } _{ L } }{ { R } _{ BE } } ,\cfrac { \Delta { I } _{ C } }{ \Delta { I } _{ B } } ,{ \beta }^{ 2 }\cfrac { { R } _{ L } }{ { R } _{ BE } } $
Question 32 Multiple Choice (Single Answer)

A common-emitter transistor amplifier has a current gain of 50. If the load resistance is $4k\Omega$ and input resistance is $500\Omega $, then the voltage gain of the amplifier is:

  1. 160
  2. 200
  3. 300
  4. 400
Question 33 Multiple Choice (Single Answer)

The current gain $\beta$ of a transistor is $50$. The input resistance of the transistor, when used in the common emitter configuration, is $1$ $k\Omega$. The peak value of the collector a.c. current for an alternating peak input voltage $0.01$ V is?

  1. $100$ $\mu A$
  2. $250$ $\mu A$
  3. $500$ $\mu A$
  4. $800$ $\mu A$
Question 34 Multiple Choice (Single Answer)

A transistor is used as a common emitter amplifier with a load resistance $2 K ohm $. The input resistance is $150 Ohm $. Base current is charged by $20 \mu A$ which results in a change in collector current by $1.5 mA$. The voltage gain of the amplifier is

  1. $900$
  2. $1000$
  3. $1100$
  4. $1200$
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