Tag: semiconductor electronics: materials, devices and simple circuits

Questions Related to semiconductor electronics: materials, devices and simple circuits

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

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $0.1$

  2. $1$

  3. $1000$

  4. $0.01$

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Correct Option: C

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

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $\alpha =\dfrac { \beta }{ 1-\beta } $

  2. $\alpha =\dfrac { \beta }{ 1+\beta } $

  3. $\alpha =\dfrac { { \beta }^{ 2 } }{ 1+{ \beta }^{ 2 } } $

  4. $\dfrac { 1 }{ \alpha } =\dfrac { 1 }{ \beta } +1$

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Correct Option: B,D

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

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $10$

  2. $20$

  3. $40$

  4. $100$

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Correct Option: D
Explanation:

Given that:
$I _c = 5\ mA$
$I _b = 50\ \mu A = 5 \times 10^{-2}\ mA$
The current gain is
$\beta = \dfrac{I _c}{I _b}$
$\beta = \dfrac{5}{5 \times 10^{-2}} = 100$

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.

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. a)100

    b)-500

  2. a)1000

    b)-500

  3. a)2000

    b)-5000

  4. a)10

    b)-5

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Correct Option: A
Explanation:

(a) $n=\frac { { \triangle v } _{ BE } }{ { \triangle | } _{ B } } =\frac { 0.02 }{ 20\times { 10 }^{ -6 } } =1k\Omega $
${ \beta  } _{ ac }=\frac { { \triangle | } _{ c } }{ { \triangle | } _{ B } } =\frac { 2\times { 10 }^{ -3 } }{ 20\times { 10 }^{ -6 } } =100$
(b) Voltage gain,${ A } _{ v }=-{ g } _{ m }{ R } _{ L }=-\left( 0.1 \right) \left( 5\times { 10 }^{ 3 } \right) =-500$. $\left( since\quad { g } _{ m }={ \beta  } _{ ac }/n \right) $

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 $100\ \mu A$?

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $6\ mA$

  2. $12\ mA$

  3. $3\ mA$

  4. $24\ mA$

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Correct Option: B
Explanation:

Given that,

Current gain$\beta =120\,A$

Base current $\Delta {{I} _{b}}=100\,\mu A$


We know that,

  $ {{\beta } _{ac}}=\dfrac{\Delta {{I} _{C}}}{\Delta {{I} _{B}}} $

 $ \Delta {{I} _{C}}=120\times 100\times {{10}^{-6}} $

 $ \Delta {{I} _{C}}=12\times {{10}^{-3}}\,A $

 $ \Delta {{I} _{C}}=12\,mA $

Hence, the collector current in the transistor is $12\ mA$

 

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

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $99$

  2. $0.99$

  3. $9.9$

  4. $990$

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Correct Option: C

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 

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $4k\Omega $

  2. $14k\Omega $

  3. $28k\Omega $

  4. $54k\Omega $

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Correct Option: C

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

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $82$

  2. $83$

  3. $8.2$

  4. $8.3$

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Correct Option: A

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

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $10k\Omega$

  2. $20k\Omega$

  3. $5k\Omega$

  4. $2.5k\Omega$

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Correct Option: A

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.

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $1.1mA$

  2. $1.01mA$

  3. $0.01mA$

  4. $10mA$

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Correct Option: B