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A 10 \Omega, 20\, \mathrm{mH} coil carrying constant current is connected to a battery of 20 \mathrm{~V} through a switch. Now after switch is opened current becomes zero in 100 \mu \mathrm{s}. The average e.m.f. induced in the coil is____________ \mathrm{V}.

Option: 1

400


Option: 2

-


Option: 3

-


Option: 4

-


\mathrm{R= 10\, \Omega }
\mathrm{L= 20 \times 10^{-3}H}

Current in the steady state ,
\mathrm{I_{0}= \frac{v}{R}= 2A}

\mathrm{Avg.Emf\: induced= e_{avg}= L\left |\frac{\Delta I}{\Delta t} \right |}
                                                      \mathrm{= 200\times10^{-3}\left | \frac{2}{100\times 10^{-6}}\right |}
\mathrm{\Rightarrow e_{avg}= 400}    

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Posted by

Rishabh Jain

Two capacitors \mathrm{A}  and \mathrm{B} having capacitors  \mathrm{10 \mu \mathrm{F}}  and  \mathrm{20 \mu \mathrm{F}}  are connected in series with a \mathrm{12 \mathrm{~V}} battery. The ratio of the charges on.

Option: 1

0.5: 1 \\


Option: 2

1: 1 \\


Option: 3

2: 1 \\


Option: 4

2: 4


when capacitors are connected in series they carry same charge. the ratio is  1: 1

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Posted by

Riya

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 Equivalent capacitor between A & B  is. 

Option: 1

\mathrm{ \frac{4}{5} \mathrm{~F} \\ }


Option: 2

\mathrm{3 / 5 \mathrm{~F} }


Option: 3

\mathrm{ 2 \mathrm{~F} \\ }


Option: 4

\mathrm{ 4 \mathrm{~F} }


Equivalent circuit-


\mathrm{C_{\text {eq. }} =\frac{|\times|}{1+1}+1 }
=\frac{1}{2}+1=3 / 2 \mathrm{~F}
\mathrm{c_{e q}=\frac{3}{2} F} and F are connected in series.

\mathrm{C_{e q}=\frac{\frac{3}{2} \times 1}{\frac{3}{2}+1}=\frac{3}{2} \times \frac{2}{5}=\frac{3}{5} F }
 

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Posted by

jitender.kumar

In the region of space the electric field is given by  \mathrm{\vec{E}=8 \hat{i}+4 \hat{j}+3 \hat{k}} . The electric flux through a surface of area 100 units in the xy plane is -

Option: 1

800 Units


Option: 2

300 units


Option: 3

400 units


Option: 4

1500 units.


we know that,

\mathrm{ \phi=\vec{E} \cdot \vec{A} }
\mathrm{ \phi=(8 \hat{\imath}+4 \hat{\jmath}+3 \hat{k}) \cdot 100 \hat{i} }
\mathrm{ \phi=300} 

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Posted by

Gaurav

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Two point charges \mathrm{+16 q } and  \mathrm{-4 q }  located at \mathrm{ x=0} and \mathrm{ x=L} . The location of a point on the x-axes from \mathrm{ x=0}, at which the net electric field due to there two charges is zero is -

Option: 1

\mathrm{ l }


Option: 2

\mathrm{ 2 l}


Option: 3

\mathrm{ L / 2}


Option: 4

\mathrm{L / 6}


\mathrm{\frac{k \cdot 16 q}{(l+x)^2} =\frac{4 k q}{x^2}}
\mathrm{\frac{x}{l+x} =\frac{1}{2} }
\mathrm{2 x =l+x }

\mathrm{\\ l =x }

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Posted by

Ritika Kankaria

A point charge of  \mathrm{0.009 \mu c}  is placed at origin. The intensity of electric field due to this charge at point \mathrm{(\sqrt{2}, \sqrt{7}, 0)} is -

Option: 1

\mathrm{(3 \sqrt{2} \hat{i}+3 \sqrt{7} \hat{j}) \mathrm{N} / \mathrm{C} }


Option: 2

\mathrm{(2 \sqrt{3} \hat{i}+3 \sqrt{7} \hat{j}) \mathrm{N} / \mathrm{C} }


Option: 3

\mathrm{(3 \sqrt{2} \hat{i}+7 \sqrt{3} \hat{j}) N / C }


Option: 4

\mathrm{(\sqrt{2} \hat{i}+7 \sqrt{3} \hat{j}) N / C}


key points.-

 \mathrm{\vec{E}=\frac{k q}{\gamma^2} \hat{\gamma} }
\mathrm{\vec{E}=\frac{k q}{\gamma^3} \vec{\gamma} }
Now


\mathrm{\vec{\gamma}=x \hat{\imath}+y \hat{\jmath} }

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Posted by

jitender.kumar

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The inward and outward electric flee for a closed surface in units of  \mathrm{N}-\mathrm{m}^2 / \mathrm{c}  are respectively 8 \times 10^3 and  \mathrm{4 \times 10^3}. Then the total charge inside the surface is -

Option: 1

4 \times 10^3 \mathrm{C}


Option: 2

-4 \times 10^3 \mathrm{c}


Option: 3

\frac{-4 \times 10^3}{\epsilon} c


Option: 4

-4 \times 10^3 \epsilon_0


\mathrm{ \therefore \quad \phi=\frac{Q}{\epsilon_0} }
\mathrm{ Q=\phi \epsilon }..........(1)
\mathrm{ \phi=\epsilon_0\left[-8 \times 10^3+4 \times 10^3\right] }
\mathrm{ \phi=-4 \times 10^3 \epsilon_0 }

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Posted by

vinayak

A charge \mathrm{q} is placed at the centre of a cube. Then the flux passing through one face of cube will be -

Option: 1

\mathrm{q / t_0 }


Option: 2

\mathrm{9 / 2t_0}


Option: 3

\mathrm{q / 3 \epsilon_0 }


Option: 4

\mathrm{2 / 6\epsilon_0}


 Total flux  \mathrm{=\frac{1}{\epsilon_0} \times q }
flex through one face \mathrm{=\frac{1}{6}}

\therefore \quad flux    \mathrm{=\frac{1}{\epsilon_0} \times 2 \times \frac{1}{6} }
\mathrm{ =2 / 6 \epsilon_0}   

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Info Expert 30

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Current drawn by the battery just after switch 's' closed is.

Option: 1

\mathrm{ 2 V / 3 R \\ }


Option: 2

\mathrm{ 3 V / 2 R \\ }


Option: 3

\mathrm{ 2 V / R \\ }


Option: 4

\mathrm{2 / R }


 when switch  S is closed this circuit will become 

 current 
\mathrm{i=\frac{V}{R_{\text {eq }}} }    \mathrm{=\frac{V}{3 R / 2}}
\mathrm{=\frac{2 V}{3 R}}
 

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Posted by

Sayak

What is the time constant of the circuit ?

Option: 1

4 sec.


Option: 2

6 sec.


Option: 3

9 sec.


Option: 4

5sec.


\mathrm{C_{\text {net }}} =0.5+0.5=1 \mathrm{f} \\


\mathrm{R_{\text {net }}=\frac{10 \times 10}{10+10}=5 \Omega }
\text { time constant } 


\tau_{\text {net }} =R_{\text {net }} C_{\text {net }} \\


=5 \times 1=5 \mathrm{sec}

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admin

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