Tag: physics

Questions Related to physics

There are $n\ sets$ of real numbers. In every set there are four real numbers in AP. Such that the square of the last term is equal to the sum of the square of the first three terms. Then: -

physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

  1. $N = 4$

  2. $N = 1000$

  3. $N = 10$

  4. $N \rightarrow \infty$

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Correct Option: C

Four  positive charges $ ( 2 \sqrt 2-1 )Q $ are arranged at corner of square . another charge q is placed at the centre of the square. resultant force acting on each corner is zero if q is :

physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

  1. $-7Q/4$

  2. $-4Q/ 7$

  3. $-Q$

  4. $none$

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Correct Option: C

A public park, in the form of a square, has an area of $(100 \pm 0.2 )m^2 $ .The side of park is :

physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

  1. $ (10 \pm 0.01 ) m $

  2. $ (10 \pm 0.1 ) m $

  3. $ (10 \pm 0.02 ) m $

  4. $ (10 \pm 0.2 ) m $

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Correct Option: A
Explanation:

Let the side length of the square park is $l$.

The area of a square is given as,

$A = {l^2}$

$100 = {l^2}$

$l = 10\;{\rm{m}}$

The error in length is given as,

$\dfrac{{\Delta A}}{A} = 2\dfrac{{\Delta l}}{l}$

$\dfrac{{0.2}}{{100}} = 2\dfrac{{\Delta l}}{{10}}$

$\Delta l = 0.01\;{\rm{m}}$

Thus, the side of the park is $\left( {10 \pm 0.01} \right)\;{\rm{m}}$.

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?

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

  1. $10$

  2. 44100$

  3. $500$

  4. $200$

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Correct Option: D

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