Tag: physics

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Questions Related to physics

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

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: -

  1. $N = 4$
  2. $N = 1000$
  3. $N = 10$
  4. $N \rightarrow \infty$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the terms of the AP be a - 3d, a - d, a + d, a + 3d (or standard a, a+d, a+2d, a+3d). Setting up the given condition that the square of the last term equals the sum of squares of the first three terms leads to a quadratic in terms of common difference or number of valid sets, which can be extended infinitely as parameters vary, yielding N -> infinity.

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

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 :

  1. $-7Q/4$
  2. $-4Q/ 7$
  3. $-Q$
  4. $none$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For the resultant force on each corner charge to be zero, the electrostatic force due to the central charge q must balance the repulsive forces from the other three corner charges. Calculating the vector components along the diagonal yields q = -7Q/4.

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

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

  1. $ (10 \pm 0.01 ) m $
  2. $ (10 \pm 0.1 ) m $
  3. $ (10 \pm 0.02 ) m $
  4. $ (10 \pm 0.2 ) m $
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $\left( {10 \pm 0.01} \right)\;{\rm{m}}$.

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

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. $200$
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

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. $0.01$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Trans-conductance (g_m) is defined as the ratio of change in collector current (Delta I_C) to the change in base-emitter voltage (Delta V_BE). Thus, g_m = 4 mA / 0.04 V = 4 * 10^-3 A / 0.04 V = 0.1 Omega^-1.

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

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. $\dfrac { 1 }{ \alpha } =\dfrac { 1 }{ \beta } +1$
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

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. $100$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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
Reveal answer Fill a bubble to check yourself
A Correct answer
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) $

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

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. $24\ mA$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $12\ mA$