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, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

Where the switch is connected in a circuit ? 

  1. in the ground wire.

  2. in the live wire

  3. in the neutral wire

  4. in live and neutral both.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A switch opens or closes an electrical circuit. If the circuit is open, no electricity flows. If the circuit is closed, electricity flows through the circuit. 
Example:
A light switch is commonly used. When you turn the switch on, the circuit closes and electricity flows through the light. When you turn the switch off, the circuit is opened and the flow of electricity stops, making the light go out. 
In our homes, we receive supply of electric power through a main supply (mains), either supported through overhead electric poles or by underground cables.The live wire and neutral wire, coming from the electric pole, enter a box fitted just outside our house which has a main fuse.
The live wire is connected to the switch because, the live wire carries a voltage of 220 V and the passage of this voltage can be disabled by switching of the circuit.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

Name the physical quantity of which the unit is ampere: 

  1. Current.

  2. Capacitance

  3. Charge

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

An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in a plasma.
The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

In an electric circuit, current starts from the-

  1. Positive terminal

  2. Either of the two terminals

  3. Negative terminal

  4. Depends upon the circuit
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The direction of an electric current is by convention the direction in which a positive charge would move. Thus, thecurrent in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery. Electrons would actually move through the wires in the opposite direction.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

The speed at which the current travels in a conductor, is nearly

  1. $3 \times 10^0 ms^{-1}$
  2. $3 \times 10^5 ms^{-1}$
  3. $4 \times 10^6 ms^{-1}$
  4. $3 \times 10^8 ms^{-1}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Current travels in a conductor at a speed approximately equal to speed of light i.e. $3\times 10^8$ $ms^{-1}$.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

In a DC circuit when a switch is closed to operate the circuit, the electrons that cause the current:

  1. travel from the negative plate of the battery to the positive plate

  2. travel from the positive plate of the battery to the negative plate

  3. travel from one resistance to the next resistance

  4. travel from the negative plate of the battery to the positive plate inside the battery

  5. travel from one atom in the circuit to the next atom
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a DC circuit , when switch is closed , the free electrons in wire are drifted from negative plate of the battery to positive plate.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

A flow of $10^{12}$ electrons per minute in a conducting wire constitutes a current of 

  1. $1.6 \times 10^{-7}\, A$
  2. $1.6 \times 10^{-8}\, A$
  3. $2.67 \times 10^{-9}\, A$
  4. `$2.67 \times 10^{-10}\, A$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Current I = q / t. Total charge q = 10^12 * 1.6*10^-19 = 1.6*10^-7 C. Time t = 60 s. I = 1.6*10^-7 / 60 = 2.67*10^-9 A.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

In a conductor, $6.25\, \times\, 10^{16}$ electrons flow from its end A to B in 2 s. Which is the current flowing through conductor? $(e\, =\, 1.6\, \times\, 10^{-19}\, C)$  

  1. $5 mA$ from B to A.
  2. $5 mA$ from A to B.
  3. $10 mA$ from A to B.
  4. $10 mA$ from B to A.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In the question, it is given that the charge of an electron is $e=1.6\times { 10 }^{ -19 }\quad C$.

Therefore, the total charge flowing through the wire in 2 seconds will be given as $6.25\times { 10 }^{ 16 }\times 1.6\times { 10 }^{ -19 }\quad C\quad =10\times { 10 }^{ -3 }\quad C$.

The rate of flow of charge is therefore $\dfrac { 10\times { 10 }^{ -3 } \  C }{ 2  \ seconds\quad  } =5\times { 10 }^{ -3 }\quad C/s$.

one C/s = one amp.

Hence, the current flowing through a conductor is $0.0005 A$, that is $5 mA$.

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

If the electric potential difference between the two points is $V$ and resistance $R$, then the current between the points will be:

  1. $VR$
  2. $V/R$
  3. $VR^2$
  4. $V/R^2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ohm's law states that voltage drop across conductor is proportional current in it.

$ V \propto I$
$ V= IR$
The proportionality constant is $R$ which known as resistance of conductor
$I= \dfrac{V}{R}$

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

A cell of e.m.f. $\varepsilon$ and internal resistance $r$ is used to send current to an external resistance R. The current drawn from the cell is :

  1. $\displaystyle \frac{\varepsilon}{(R\, +\, r)}$
  2. $\displaystyle \frac{\varepsilon Rr}{R+r}$
  3. $\displaystyle \frac{\varepsilon R}{R+r}$
  4. $\displaystyle \frac{\varepsilon r}{R+r}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Batteries and cells have an  internal resistance (r) which is measured in ohms. When electricity flows around a circuit, the internal resistance of the cell itself resists the flow of current and so thermal (heat) energy is wasted in the cell itself.

$\varepsilon =I(R+r)$

where,

$\varepsilon $ = electromotive force in volts, V

I = current in amperes, A

R = resistance of the load in the circuit in ohms,

r = internal resistance of the cell in ohms.

The above equation can be written as $I=\dfrac { \varepsilon  }{ R+r } $.

Hence, the expression for the current drawn from the cell is $I=\dfrac { \varepsilon  }{ R+r } $.
Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

It is possible to measure the passage of $50$ electrons per second with a certain sensitive device. This corresponds to a current of :

  1. $8 \times 10^{-18} A$
  2. $1.6 \times 10^{-20} A$
  3. $8 \times 10^{-20} A$
  4. $1.6 \times 10^{-19} A$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation


Let number of electrons per second be n.
Given,
$e = 1.6 \times 10^{-19} C$ ,  $n =50 $
The current is defined as rate of flow of charge,
$I = \dfrac{q}{t} $ 
Hence,
$I = n \times e $

Substituting values,
$I = 50 \times 1.6\times 10^{-19} = 8 \times 10^{-18} A $

Multiple choice physics electric current, potential difference and resistance electric potential and potential difference potential difference current in electric circuits

On a bulb is written 220 volt and 60 watt. Find out the resistance of the bulb and the value of the current flowing through it:

  1. $806.66 ohm\ and\ 0.27 ampere$
  2. $500 ohm \ and\ 2 amphere$
  3. $200 ohm \ and\ 4 ampere$
  4. $100 ohm \ and\ 1 ampere$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$R=\dfrac {V^2}{P}=\dfrac {(60^2)}{220}$
$=806.66 \Omega$
$I=\dfrac {P}{V}$
$=\dfrac {6-0}{220}=0.27$