Tag: electric circuits

Questions Related to electric circuits

n identical cells are joined in series with its two cells A and B in the loop with reversed polarities.
EMF of each shell is E and internal resistance r. Potential difference across cell A or B is:

physics electric circuits combination of resistors combination of cells combinations of components

  1. $\dfrac{2E}{n}$

  2. $2E|1-\dfrac{1}{n}|$

  3. $\dfrac{4E}{n}$

  4. $2E|1-\dfrac{2}{n}|$

Show answer
Correct Option: C
Explanation:

Number of cells $=n$

EMF of each cell $=E$
Internal resistance of each cell, $= r$

All the cells are in series.
Thus,
Total internal resistance, $R=nr$
Total EMF, $e=nE$

As the two cells are connected in reverse polarity, these two cells will cancel-out the contribution of other two cells in the loop.

Then, the net EMF across the circuit will be
$E _{eq}=nE-4E$

The current $I$ in the circuit $=\dfrac{nE-4E}{nr}$

Voltage across the opposite connected batteries, $V=E-Ir$
$V=E-\dfrac{E(n-4)}{nr}\times r$
$V=\dfrac{4E}{n}$

Therefore, the voltage across the battery A or B will be $\dfrac{4E}{n}$.


Two similar cells, whether joined in series or in parallel, have the same current through an external resistance of $2\Omega$. The internal resistance of each cell is

physics electric circuits combination of resistors combination of cells combinations of components

  1. $1\Omega$

  2. $2\Omega$

  3. $0.5\Omega$

  4. $1.5\Omega$

Show answer
Correct Option: B
Explanation:

In series, current, $i _{1} = \dfrac {2E}{2 + 2r}$
In parallel, current, $i _{2} = \dfrac {E}{2 + \dfrac {r}{2}} = \dfrac {2E}{4 + r}$
According to the question
Since, $i _{1} - i _{2} \Rightarrow \dfrac {2E}{4 + r} = \dfrac {E}{2 + 2r}$
$\Rightarrow r = 2\Omega$.

36 identical cell each having emf 1.5 volt and internal resistance $ 0.5 \Omega$ are connected in series with an external resistance of $12 \Omega$ .If 6 cells are wrongly connected then current through the circuit will be 

physics electric circuits combination of resistors combination of cells combinations of components

  1. 1.2 A

  2. 1 A

  3. 2 A

  4. 4 A

Show answer
Correct Option: A
Explanation:

Total resistance in the circuit is, $R _T=36\times0.5+12=30\Omega$

Net EMF in the circuit is, $E _T=(30-6)\times1.5=36V$

So, current in the circuit is, $I=\dfrac{E _T}{R _T}=\dfrac{36}{30}=1.2A$

When n number identical cell of emf E and internal resistance is connected in series, the net internal resistance of the system will be  

physics electric circuits combination of resistors combination of cells combinations of components

  1. $\dfrac{nEr}{1+E}$

  2. $n^2r$

  3. $nr$

  4. $n/r$

Show answer
Correct Option: C
Explanation:

It is a common fact that when current flows the circuit, connected with a magnetic compass, the magnetic needle in the compass will show deflection due to the magnetic effect of the current. Magnetic lines of forces are created around the coil of wire and this caused the needle to deflect according to the direction of the current.
In this case, when the number of cells in the circuit is increased, the current through the circuit is also increased. This is because, the increase in cells indicates more current in the circuit. 
Hence, as the current in the circuit is increased, the deflection in the magnetic compass also increase further.


A cell of constant emf first connect to a resistance $R _1$ and then to connected to the resistance $R _2.$ If power delivered in both cases in the same then internal resistance of the cell

physics electric circuits combination of resistors combination of cells combinations of components

  1. $\dfrac { R _ { 1 } - R _ { 2 } } { 2 }$

  2. $ { R _ { 1 } + R _ { 2 } } $

  3. $\sqrt { R _ { 1 } R _ { 2 } }$

  4. $\sqrt { R _ { 1 } + R _ { 2 } / 2 }$

Show answer
Correct Option: A
Explanation:

The cell has constant emf$,$

Resistance is $R _1$ and $R _2$

$P = V _2 / R _1 + r$

$P = V _2 / R _2 - r$

$( R _1- R _2 ) / 2$

The internal resistance of the cell is $( R _1 - R _2 ) / 2$

Hence,

option $(A)$ is correct answer.

A battery is delivering same power to resistance $R _1$ and $R _2$ . Then find the internal resistance of battery :

physics electric circuits combination of resistors combination of cells combinations of components

  1. $\dfrac { R _ { 1 } - R _ { 2 } } { 2 }$

  2. ${ R _ { 1 } + R _ { 2 } }$

  3. $ \sqrt { R _ { 1 } + R _ { 2 } }$

  4. $\sqrt { R _ { 1 } + R _ { 2 } / 2 }$

Show answer
Correct Option: A
Explanation:
$\begin{array}{l} P=\frac { { { V^{ 2 } } } }{ { { R^{ 2 } }+r } } -------\left( 1 \right)  \\ P=\frac { { { V^{ 2 } } } }{ { { R^{ 2 } }-r } } -------\left( 2 \right)  \\ solve\, \, eqation\left( 1 \right) and\left( 2 \right)  \\ =\dfrac { { { R _{ 1 } }-{ R _{ 2 } } } }{ 2 }  \end{array}$
Hence,
option $(A)$ is correct answer.

Electricians use rubber gloves while working because

physics electric circuits precaution with the electrical circuit precautions to be taken while dealing with current devices used to protect from shock of electric current

  1. rubber is an insulator

  2. rubber is a good conductor

  3. it is easy to work while wearing gloves

  4. none ofthese

Show answer
Correct Option: A
Explanation:

Electricians use rubber gloves while working because rubber is an insulator and hence prevents them from getting an electric shock.

Which of the following is not a safety measure commonly used in electric circuits.

physics electric circuits precaution with the electrical circuit precautions to be taken while dealing with current devices used to protect from shock of electric current

  1. An electric fuse is connected in parallel

  2. Proper earthing of all electric circuit is done

  3. Fuse protects the circuit from overloading

  4. All

Show answer
Correct Option: A
Explanation:

An electric fuse is connected in parallel. This is not a safety measure. Fuse is always connected in series.

In domestic electrical circuit, switches are used in

physics electric circuits precaution with the electrical circuit precautions to be taken while dealing with current devices used to protect from shock of electric current

  1. Neutral wire

  2. Earth wire

  3. Live wire

  4. All of these

Show answer
Correct Option: C
Explanation:

Switches are connected in live wire so that when the switch is in off position, no current flows through circuit. As a result there will not be any danger of electrical shock.