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 ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

An inductor coil,a capacitor and an alternating source of virtual value 36 V are connected in series.When the frequency of the source is varied, a maximum virtual current 4  A is observed. If this inductor coil is connected to a battery of emf 18V and internal resistance$ 9\Omega$, the current in the circuit will be:

  1. 1 A

  2. 2 A

  3. 3 A

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given that,

e. m. f = $18\ V$

${{E} _{rms}}=36V$

Internal resistance $r=9\Omega $

Current ${{I} _{rms}}=4\,A$

Now, the external resistance is

We know that,

  $ R=\dfrac{E _{rms}}{I _{rms}} $

 $ R=\dfrac{36}{4} $

 $ R=9\,\Omega  $


When the inductor coil is connected to a 18 V battery with 9 $\Omega$ internal resistance: 

Now, net resistance is

  $ {{R} _{net}}=R+r $

 $ {{R} _{net}}=9+9 $

 $ {{R} _{net}}=18\,\Omega  $


Now, the current is

  $ I=\dfrac{e.m.f}{{{R} _{net}}} $

 $ I=\dfrac{18}{18} $

 $ I=1\,A $

 Hence, the current is $1\ A$ in the circuit

Multiple choice ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

In a choke coil, the reactance $X _L$ and resistance R are such that :-

  1. $X _L = R$
  2. $X _L >>> R$
  3. $X _L <<< R$
  4. $X _L = \infty$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A choke coil is designed to limit current in AC circuits with minimal power dissipation. Since power loss P = I^2 * R, we need R to be as small as possible compared to the inductive reactance X_L.

Multiple choice ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

A closed circuit consists of a source of emf $E$ and an inductor coil of inductance $L$, connected in series. The active resistance of whole circuit is $R$. At the moment $t=0$. inductance of coil abruptly decreased to $L/n$. Then current in the circuit immediately after, is:

  1. $zero$
  2. $E/R$
  3. $\dfrac{nE}{R}$
  4. $\dfrac{E}{nR}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The magnetic flux through an inductor cannot change instantaneously. Phi = L * I. If L changes to L/n, the current I must change to I' such that L * I = (L/n) * I'. Therefore, I' = n * I. Since the initial current was I = E/R, the new current is nE/R.

Multiple choice ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

A $0.21\space H$ inductor and a $12\Omega$ resistance are connected in series to a $220\space V, 50\space Hz$ ac source. The current in the circuit is :

  1. $\displaystyle\frac{220}{\sqrt{4400}}A$
  2. $\displaystyle\frac{22}{3\sqrt5}A$
  3. $\displaystyle\frac{220}{\sqrt{4550}}A$
  4. $\displaystyle\frac{22}{5\sqrt3}A$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$ X _L = L 2 \pi f = 0.21 \times 314 \Omega $
$ R = 12 \Omega $
$ I = \dfrac{ 220}{ \sqrt{ X _L^2 + R^2 } } = 3.28 = \dfrac{22}{3\sqrt{5}} A  $

Multiple choice ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

An A.C voltage $V=5\cos { \left( 1000t \right) V } $ is applied to a L-R series circuit of inductance $3mH$ and resistance $4\Omega$. The value of maximum current in the circuit is  _______ A

  1. $0.8$
  2. $1.0$
  3. $\cfrac{5}{7}$
  4. $\cfrac { 5 }{ \sqrt { 7 } } $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$V=5\cos { \left( 1000t \right) V } $

The standard equation for the voltage is:
$V={ V } _{ 0 }\cos { \omega t } $

So, from the equation, ${ V } _{ 0 }=5volt;\omega =1000rad/s$
$L=3\times { 10 }^{ -3 }H,R=4\Omega $

Maximum current $10=\cfrac { { V } _{ 0 } }{ Z } \quad $
$10=\cfrac { 5 }{ \sqrt { { \omega  }^{ 2 }{ L }^{ 2 }+{ R }^{ 2 } }  } =\cfrac { 5 }{ 5 } =1A\quad \quad $

Multiple choice physics units and measurement: error analysis accuracy of measurement accuracy and precision accuracy, precision and uncertainty in measurement

Accuracy of potentiometer can be easily increased by :

  1. increasing resistance of wire

  2. decreasing resistance of wire

  3. increasing the length of wire

  4. decreasing the length of wire
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Accuracy of potentiometer can be easily increased by decreasing the potential gradient across the potentiometer wire and that can be done by increasing its length.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

If $\vartheta $ is the phase difference and T is time period then time difference between current and voltage is ;

  1. $T \vartheta $
  2. $\dfrac { T }{ \vartheta } $
  3. $\dfrac { 2\pi T }{ \vartheta } $
  4. $\dfrac { T \vartheta }{ 2\pi }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The phase difference theta corresponds to a time difference delta_t. Since 2*pi radians corresponds to one time period T, the ratio is delta_t/T = theta/(2*pi). Thus, delta_t = (T * theta) / (2*pi).

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

The resistance of a coil for dc is $R$ ohms. When connected to ac supply the total resistance offered by circuit to ac current.

  1. Will remain same

  2. Will increase

  3. Will decrease

  4. Will be zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Resistance offered by coil is same for $AC$ as well as $DC.$ So, Resistance will not change.

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

Assertion: Ohm's law cannot be applied to a.c circuit. 
Reason: Resistance offered by capacitor for a.c source depends upon the frequency of the source. 

  1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

  2. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion.

  3. If Assertion is true statement but Reason is false.

  4. If both Assertion and Reason are false statements.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Assertion statement is false.
Ohm's can also be applied to a.c circuit.
Reason statement is correct.
Capacitor resistance, $R _C =\dfrac{1}{wC} = \dfrac{1}{(2\pi \nu)C}$
Multiple choice physics electric current and its effects heating effect of electric current- uses applications of heating effect of electric current coil and fuse

An electric iron is based upon the principle of

  1. heating effect ofcurrent

  2. magnetic effect ofcurrent

  3. chemical effect ofcurrent

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An electric iron is based on the principle of heating effect of current that heat is produced in the nichrome wire used in the iron due to the current flowing through it.

Multiple choice physics electric current and its effects heating effect of electric current- uses applications of heating effect of electric current coil and fuse

The overheating of electrical wiring in any circuit due to the flow of large current through it is called _________ of the electric circuit.

  1. over heating

  2. heating effect

  3. cooling effect

  4. see-back effect
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The overheating of electrical wiring in any circuit due to the flow of large current through it is called overloading of electric current.

Multiple choice physics alternating current power in ac circuits average power in ac circuit and power factor power in ac circuit

An electrical device draws 2 kW power from ac mains voltage 223 V(rms). The current differs lags in phase by $\phi = tan^{-1} \left ( -\frac{3}{4} \right )$ as compared to voltage. The resistance R in the circuit is:

  1. 15 $\Omega$
  2. 20 $\Omega$
  3. 25 $\Omega$
  4. 30 $\Omega$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here, $P \, = \, 2 \, kW \, = \, 2 \, \times \, 10^3W$
$V _{rms} \, = \, 233 \, V, tan \, \phi \, = \, -\dfrac{3}{4}$
$As, \, P \, = \, \dfrac{V^2 _{rms}}{Z}$

$\Rightarrow \, Z \, = \, \dfrac{V^2 _{rms}}{P} \, = \, \dfrac{(223)^2}{2000} \, =  \dfrac{49729}{2000} \, = \, 24.86 \, \Omega \, or \, Z \, = \, 25 \, \Omega$

$\tan \, \phi \, = \, \dfrac{X _C \, - \, X _L}{R} \, = \, - \dfrac{3}{4} \, \therefore \, X _C \, - \, X _L \, = \, -\dfrac{3}{4} R.$

AS, $Z^2 \, = \, R^2 \, + \, (X _C \, - \, X _L)^2$
$\therefore \, (25)^2 \, = \, R^2 \, + \, \left(-\dfrac{3}{4} \, R \right)^2$
$625 \, = \, \dfrac{25 \, R^2}{16}.$
$R^2 \, = \, \dfrac{625 \, \times \, 16}{25} \,  \, \Rightarrow \, R \, = \, 20 \, \Omega$

Multiple choice physics alternating current power in ac circuits average power in ac circuit and power factor power in ac circuit

A coil has a resistance $ 10 \Omega $ and an inductance of 0.4 henry. It is connected to an AC source of $ 6.5 V , \frac {30} { \pi } Hz. $ The average power consumed in the circuit, is :

  1. $ \cfrac {5} { 8} W $
  2. $ \cfrac {4} {3} W $
  3. $ \cfrac {3} {8} W $
  4. $ \cfrac {6} {7} W $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The impedance Z = sqrt(R^2 + XL^2). XL = 2 * pi * f * L = 2 * pi * (30/pi) * 0.4 = 24 ohms. Z = sqrt(10^2 + 24^2) = sqrt(100 + 576) = 26 ohms. Current I = V/Z = 6.5 / 26 = 0.25 A. Power P = I^2 * R = (0.25)^2 * 10 = 0.0625 * 10 = 0.625 W, which is 5/8 W.

Multiple choice physics alternating current power in ac circuits average power in ac circuit and power factor power in ac circuit

In a series $LCR$ circuit $K=200\ \Omega$ and the voltage and frequency of the main supply are $220\ V$ and $50\ Hz$ respectively. On taking out the capacitor from the circuit, the current leads the voltage by ${30}^{o}$. On taking out the indicator from the circuit the current leads the voltage by ${30}^{o}$. The power dissipated in the $LCR$ circuit is :

  1. $342\ W$
  2. $305\ W$
  3. $209\ W$
  4. $242\ W$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$P=\cfrac { { V } _{ rms }^{ 2 } }{ R } cos\phi =\cfrac { { 220 }^{ 2 } }{ 200 } cos30°=209W$