Physics

Current Electricity and Circuits

377 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 chemical effects of electric current study about cells electric cell types of cells

An inductor coil stores $U$ when a current is passed through it and dissipates heat energy at the rate of $P .$ The time constant of the circuit when this connected across a battery of zero internal resistance is:


  1. $\frac { 4 U } { P }$
  2. $\frac { U } { P }$
  3. $\frac { 2 U } { P }$
  4. $\frac { 2 P } { 6U }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Energy stored U = (1/2)LI^2. Power dissipated P = I^2R. Time constant tau = L/R. From equations, L = 2U/I^2 and R = P/I^2. Thus, tau = (2U/I^2) / (P/I^2) = 2U/P.

Multiple choice physics chemical effects of electric current study about cells electric cell types of cells

A wire of length $L$ and $3$ identical cells of negligible internal resistances are connected in series. Due to the current, the temperature of the wire is raised by $\Delta\ T$ in a time $t$. A number $N$ of similar cells is now connected in series with a wire of the same material and cross-section but of length $2\ L$. The temperature of the wire is raised by the same amount $\Delta\ T$ in the same time. The value of $N$ is

  1. $4$
  2. $6$
  3. $8$
  4. $9$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics alternating currents sinusoidal current types of current movement of charge

A 220 V, 50 Hz AC source is connected to an inductance of 0.2 H and resistance of 20 $\Omega$ in series. The current in the circuit is :

  1. $3.33 A$
  2. $33.3 A$
  3. $15 A$
  4. $5 A$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given, V =220 volts, f=50 Hz, L =0.2 H, R = 20 $\Omega$


$X _L =2\pi fL=2 \times 3.14 \times 50 \times 0.2$

$= 100 \times  0.628 = 62.80\Omega$

$Z = \sqrt{X^2 _L + R^2} = \sqrt{(62.8)^2 + 20^2}$

$I = \displaystyle \frac{V}{Z} = \frac{220}{\sqrt{43473.84}} = 3.33A$

Multiple choice physics alternating currents sinusoidal current types of current movement of charge

An alternating voltage $E=200\sqrt{2}\sin (100t)$ is connected to $1$ microfarad capacitor through AC ammeter. The reading of ammeter shall be.

  1. $10$mA
  2. $20$mA
  3. $40$mA
  4. $80$mA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Reading of ammeter $=I _{rms}=\displaystyle \frac{V _{rms}}{X _C}=\frac{V _0\omega C}{\sqrt 2}$
$=\displaystyle\frac{200\sqrt 2\times 100\times (1\times 10^{-6})}{\sqrt 2}=2\times 10^{-2} A$
$=20 mA$

Multiple choice physics alternating currents sinusoidal current types of current movement of charge

An alternating voltage is given by $e = (6\sin \omega t + 8\cos \omega t)volt$. The instantaneous value of voltage is given by

  1. $5\sqrt {2}V$
  2. $10V$
  3. $10\sqrt {2}V$
  4. $\dfrac {10}{\sqrt {2}}V$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The expression e = 6*sin(wt) + 8*cos(wt) can be written as e = 10 * (0.6*sin(wt) + 0.8*cos(wt)). Using sin(A+B), this is e = 10*sin(wt + alpha), where the amplitude is 10V.

Multiple choice physics alternating currents sinusoidal current types of current movement of charge

A coil, a capacitor and an ac source of rms voltage $24V$ are connected in series. By varying the frequency of the source, a maximum rms current of $6A$ is observed. If this coil is connected to a battery of emf $12V$ and internal resistance $4\Omega$, the current through will be

  1. $2.4A$
  2. $1.8A$
  3. $1.5A$
  4. $1.2A$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

At resonance, the impedance Z = R. Since V_rms = 24V and I_rms = 6A, R = 24/6 = 4 ohms. When connected to a 12V battery with 4 ohms internal resistance, the total resistance is 4+4 = 8 ohms. Current = V/R_total = 12/8 = 1.5A.

Multiple choice physics alternating currents sinusoidal current types of current movement of charge

A mixer of $1000\Omega$ resistance is connected to an $A.C.$ source of $200\ volts$ and $50\ cycle/sec$. The value of average potential difference across the mixer will be:

  1. $308\ volts$
  2. $264\ volts$
  3. $220\ volts$
  4. $zero$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The average value of a symmetric alternating current (like a sine wave) over one full cycle is zero, as the positive and negative half-cycles cancel each other out.

Multiple choice physics alternating currents sinusoidal current types of current movement of charge

In an A.C. circuit a resistance R is connected in series with an inductance L.The phase difference between voltage and current is $45^o$. Then what will be the value of inductive reactance?

  1. R
  2. $\frac{R}{2}$
  3. $\frac{R}{4}$

  4. 2R
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In an R-L series circuit, the phase difference is given by tan(phi) = X_L / R. Since phi = 45 degrees, tan(45) = 1, which implies X_L / R = 1, or X_L = R.

Multiple choice physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

A light emitting diode (LED) has a voltage drop of 2 V across it and passes a current of 10 mA. When it operates with a 6 V battery through a limiting resistor R, the value of R is 

  1. 200 $\Omega$
  2. 400 $\Omega$
  3. 40 $k\Omega$
  4. 4 $k\Omega$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Light emitting diode is a forward biased P-N junction which emits light.

The voltage across it = 2 v

Battery voltage = 6 v

Hence total voltage in the circuit = V = 6 - 2 = 4 v

since a LED has 0 resistance in the forward biased region, total resistance in the circuit

= 0 + r = r

current I = 10 mA = 10/1000 A = 0.01 A

we know that,

R = V/I

=> r = 4/0.01 = 400Ω

Hence the value of the limiting resistor is 400Ω

Multiple choice physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

The relation between dynamic plate resistance $\left( r _ { p } \right)$ of a vacuum diode and plate current in the space charge limited region, is 

  1. $r _ { p } \propto I _ { p }$
  2. $r _ { p } \propto I _ { p } ^ { 3 / 2 }$
  3. $r _ { p } \propto \frac { 1 } { I _ { p } }$
  4. $r _ { p } \propto \frac { 1 } { \left( I _ { p } \right) ^ { 1 / 3 } }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics magnetic effects of electric current direct current types of current movement of charge

If the instantaneous emf and the instantaneous current equations of an A.C. circuit are respectively 
$e = E _0 sin(\omega t - \pi/6), i = I _0 sin (\omega t + \pi/6)$, then the phase difference between voltage and current is :

  1. $\dfrac{\pi}{3}$

  2. zero
  3. $\dfrac{\pi}{2}$
  4. $\dfrac{\pi}{6}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Phase of current   $\phi _1 = wt +\dfrac{\pi}{6}$

Phase of emf    $\phi _2 = wt-\dfrac{\pi}{6}$
Phase difference   $\Delta \phi = \phi _1-\phi _2$
$\implies \Delta \phi = (wt+\dfrac{\pi}{6})-(wt-\dfrac{\pi}{6}) = \dfrac{\pi}{3}$