Physics

Current Electricity and Circuits

450 Questions

Current electricity and circuits questions cover resistors, EMF, internal resistance, and power calculations in series and parallel configurations. Solving these builds a strong understanding of electrical principles and circuit analysis. These physics problems are highly relevant for technical and science aptitude tests.

Resistor combinationsPower dissipationEMF and internal resistanceAC circuit analysisOperational amplifiers

Current Electricity and Circuits Questions

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

A resistor is marked with the rings coloured brown, black, green and gold. The resistance in ohm is?

  1. $(3.5\times 10^5\pm 5\%)$
  2. $(1.10\times 10^5\pm 10\%)$
  3. $(8\times 10^6\pm 5\%)$
  4. $(1\times 10^6\pm 5\%)$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
By color coding
Brown Black Green Gold
$1             .0   \times10^6 \pm5\%$
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 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 $12\ mA$

 

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

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

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. $8.3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The current gain beta is defined as delta_Ic / delta_Ib. Since delta_Ie = delta_Ic + delta_Ib, delta_Ib = delta_Ie - delta_Ic = 8.3mA - 8.2mA = 0.1mA. Thus, beta = 8.2mA / 0.1mA = 82.

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

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. $2.5k\Omega$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Output resistance r_o = delta_Vcb / delta_Ic = 0.5V / 0.05mA = 0.5 / 0.00005 = 10,000 Ohms = 10k Ohm.

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

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. $10mA$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given beta = 100, delta_Ic = 1mA. Since beta = delta_Ic / delta_Ib, delta_Ib = 1mA / 100 = 0.01mA. Then delta_Ie = delta_Ic + delta_Ib = 1mA + 0.01mA = 1.01mA.

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

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. $50$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Power gain = $(Current \, gain)^2 \left(\dfrac{R _{out}}{R _{in}} \right)$
$10^6 = \beta^2 \times \dfrac{10^4}{100}$
$\beta = 100$

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

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. $560$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Voltage amplification, $\displaystyle A _v = \beta \dfrac{R _0}{R _i} = 60 \times \dfrac{5000}{500} = 600$

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

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. $620\ V$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle \dfrac{V _0}{V _m} = \dfrac{R _0}{R _{in}} \times \beta = \dfrac{5 \times 10^3 \times 62}{500} = 10 \times 62 = 620$

$V _0 = 620 \times V _{in} = 620 \times 0.01 = 6.2\ V$

$\therefore V _0$ = $6.2\ V$