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

Two cells of emf's $3V$ and $3V$ have internal resistances  $1.5\Omega\ &\ 1\Omega$ are connected in parallel across $3\Omega,$ such that they send the current through $3\Omega$ in same direction calculate the p.d. across $3\Omega$ resistor.

  1. 3V

  2. 4V

  3. 1.5V

  4. 2.5V
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Two cells of emf 3V with internal resistances 1.5 ohm and 1 ohm are connected in parallel, so their equivalent emf E_eq = (E1/r1 + E2/r2) / (1/r1 + 1/r2) = (3/1.5 + 3/1) / (1/1.5 + 1/1) = (2 + 3) / (2/3 + 1) = 5 / (5/3) = 3V. The equivalent internal resistance r_eq = (1.5 * 1) / (1.5 + 1) = 1.5 / 2.5 = 0.6 ohm. When connected across a 3 ohm resistor, the potential difference is V = E_eq * R / (R + r_eq) = 3 * 3 / (3 + 0.6) = 9 / 3.6 = 2.5V.

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

 What are the three basic parts of a cell?

  1. Electrodes, electrolyte, container

  2. Electrodes, acid, water

  3. Anode, cathode, ions

  4. Anode, load, depolarize
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A cell is basically a source of energy or electrical energy; there are three basic things required to make a cell work.

$i)$ The source of energy,(electrolyte)
$ii)$ The conduction medium to transfer energy (electrodes)
$iii)$ The contained to stare the energy. 

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 eddy currents motional emf electromagnetic induction electromagnetic induction and alternating currents physics

Read the following statements and answer whether the given statement is true or false.

Eddy current involves loss of energy in the form of heat.

  1. True

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

Eddy currents (also called Foucault currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor due to Faraday's law of induction. 

Eddy current involves loss of energy in the form of heat. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer. 
The statement is true.

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