1
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

When the switch S, in the circuit shown, is closed, then the value of current i will be :

A
3A
B
5A
C
4A
D
2A

Explanation



Let the voltage at C = V

$$ \therefore $$   Using KCL law,

i1 + i2 = i

$$ \Rightarrow $$   $${{20 - V} \over 2} + {{10 - V} \over 4}$$ = $${{V - 0} \over 2}$$

$$ \Rightarrow $$   V = 10 volts.

$$ \therefore $$   i = $${{10} \over 2}$$

= 5A
2
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

For a uniformly charged ring of radius R, the electric field on its axis has the largest magnitude at a distance h from its center. Then value of h is :
A
$${R \over {\sqrt 5 }}$$
B
$${R \over {\sqrt 2 }}$$
C
R
D
R$$\sqrt 2 $$

Explanation



Electric field on the axis of the ring,

$$E = {{KQh} \over {{{\left( {{R^2} + {h^2}} \right)}^{{3 \over 2}}}}}$$

For maximum electric field,

$${{dE} \over {dh}} = 0$$

$$ \Rightarrow $$   $$h = {R \over {\sqrt 2 }}$$
3
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

Drift speed of electrons, when 1.5 A of current flows in a copper wire of cross section 5 mm2, is $$\upsilon $$. If the electron density in copper is 9 $$ \times $$ 1028/m3 the value of $$\upsilon $$. in mm/s is close to (Take charge of electron to be = 1.6 $$ \times $$ 10$$-$$19C)
A
0.02
B
3
C
2
D
0.2

Explanation

We know,

I = neAVd

$$ \therefore $$   Vd = $${{\rm I} \over {neA}}$$

=   $${{1.5} \over {9 \times {{10}^{28}} \times 1.6{ \times ^{ - 19}} \times 5 \times {{10}^{ - 6}}}}$$

=   0.02 m/s
4
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

A parallel plate capacitor is made of two square plates of side 'a', separated by a distance d (d < < a). The lower triangular portion is filled with a dielectric of dielectric constant K, as shown in the figure. Capacitance of this capacitor is :

A
$${{K{ \in _0}{a^2}} \over {2d(K + 1)}}$$
B
$${{K{ \in _0}{a^2}} \over {d(K - 1)}}\ln K$$
C
$${{K{ \in _0}{a^2}} \over d}\ln K$$
D
$${1 \over 2}{{K{ \in _0}{a^2}} \over d}$$

Explanation





Let the capacitance of the upper part of the strip of length dx is dC1 and lower part of the strip is dC2

$$ \therefore $$   dC1 = $${{{\varepsilon _0}\,adx} \over {d - y}}$$

and dC2 = $${{K{\varepsilon _0}\,adx} \over y}$$

Here dC1 and dC2 are in series.

So, equivalent capacitance,

$${1 \over {dC}}$$ = $${1 \over {d{C_1}}} + {1 \over {d{C_2}}}$$

$$ \Rightarrow $$    $${1 \over {dC}}$$ = $${{d - y} \over {{\varepsilon _0}a\,dx}} + {y \over {{\varepsilon _0}K\,adx}}$$

$$ \Rightarrow $$   $${1 \over {dC}}$$ = $${1 \over {{\varepsilon _0}\,adx}}$$ ( d $$-$$ y + $${y \over K}$$)

$$ \Rightarrow $$   dC = $${{{\varepsilon _0}\,adx} \over {\left( {d - y} \right) + {y \over K}}}$$

We can divide entire parallel plate capacitor into similar part like the strip of length dx and all the strips will have common end A and B. So they are in parallel.

So equivalent capacitance is the sum of all the strips capacitance.

$$ \therefore $$   $$\int {dC} $$ = $$\int\limits_0^a {{{{\varepsilon _0}\,adx} \over {\left( {d - y} \right) + {y \over K}}}} $$

$$ \Rightarrow $$   C = $$\int\limits_0^a {{{{\varepsilon _0}\,a\,dx} \over {\left( {d - y} \right) + {y \over K}}}} $$

From above diagram you can find this $$ \to $$



tan$$\theta $$ = $${y \over x}$$

Also tan$$\theta $$ = $${d \over a}$$

$$ \therefore $$   $${y \over x}$$ = $${d \over a}$$

$$ \Rightarrow $$   y = $${d \over a}$$ x

By putting this value of y in the integration we get,

C = $$\int\limits_0^a {{{{\varepsilon _0}\,a\,dx} \over {d - {d \over a}x + {d \over {Ka}}x}}} $$

= $$\int\limits_0^a {{{{\varepsilon _0}\,a\,dx} \over {d + \left( {{1 \over K} - 1} \right){d \over a}x}}} $$

= $$\int\limits_0^a {{{{\varepsilon _0}\,{a^2}\,dx} \over {da + \left( {{{1 - K} \over K}} \right)xd}}} $$

= $$\int\limits_0^a {{{K{\varepsilon _0}\,{a^2}\,dx} \over {Kda + \left( {1 - K} \right)xd}}} $$

= $${{K{\varepsilon _0}{a^2}} \over {d\left( {1 - k} \right)}}\left[ {\ln \left( {\left( {1 - K} \right)x + Ka} \right)} \right]_0^a$$

= $${{K{\varepsilon _0}{a^2}} \over {d\left( {1 - k} \right)}}\left[ {\ln \left( a \right) - \ln \left( {Ka} \right)} \right]$$

= $${{K{\varepsilon _0}\,{a^2}} \over {d\left( {1 - k} \right)}}\ln \left( {{a \over {Ka}}} \right)$$

= $${{K{\varepsilon _0}\,{a^2}} \over {d\left( {1 - k} \right)}}\ln \left( {{1 \over K}} \right)$$

= $${{K{\varepsilon _0}\,{a^2}} \over {d\left( {1 - k} \right)}}\ln \left( K \right)$$

Questions Asked from Current Electricity

On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Name Indicates No of Questions
AIEEE 2002 (6)
keyboard_arrow_right
AIEEE 2003 (6)
keyboard_arrow_right
AIEEE 2004 (10)
keyboard_arrow_right
AIEEE 2005 (7)
keyboard_arrow_right
AIEEE 2006 (5)
keyboard_arrow_right
AIEEE 2007 (2)
keyboard_arrow_right
AIEEE 2008 (4)
keyboard_arrow_right
AIEEE 2010 (2)
keyboard_arrow_right
AIEEE 2011 (1)
keyboard_arrow_right
AIEEE 2012 (1)
keyboard_arrow_right
JEE Main 2013 (Offline) (2)
keyboard_arrow_right
JEE Main 2014 (Offline) (1)
keyboard_arrow_right
JEE Main 2015 (Offline) (2)
keyboard_arrow_right
JEE Main 2016 (Offline) (1)
keyboard_arrow_right
JEE Main 2016 (Online) 9th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2016 (Online) 10th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2017 (Offline) (3)
keyboard_arrow_right
JEE Main 2017 (Online) 8th April Morning Slot (2)
keyboard_arrow_right
JEE Main 2017 (Online) 9th April Morning Slot (3)
keyboard_arrow_right
JEE Main 2018 (Offline) (2)
keyboard_arrow_right
JEE Main 2018 (Online) 15th April Morning Slot (2)
keyboard_arrow_right
JEE Main 2018 (Online) 15th April Evening Slot (2)
keyboard_arrow_right
JEE Main 2018 (Online) 16th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 9th January Morning Slot (4)
keyboard_arrow_right
JEE Main 2019 (Online) 9th January Evening Slot (3)
keyboard_arrow_right
JEE Main 2019 (Online) 10th January Morning Slot (6)
keyboard_arrow_right
JEE Main 2019 (Online) 10th January Evening Slot (4)
keyboard_arrow_right
JEE Main 2019 (Online) 11th January Morning Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 11th January Evening Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 12th January Morning Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 12th January Evening Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 8th April Morning Slot (6)
keyboard_arrow_right
JEE Main 2019 (Online) 8th April Evening Slot (4)
keyboard_arrow_right
JEE Main 2019 (Online) 9th April Morning Slot (3)
keyboard_arrow_right
JEE Main 2019 (Online) 9th April Evening Slot (4)
keyboard_arrow_right
JEE Main 2019 (Online) 10th April Morning Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 10th April Evening Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 12th April Morning Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 12th April Evening Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 7th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2020 (Online) 7th January Evening Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 8th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2020 (Online) 8th January Evening Slot (4)
keyboard_arrow_right
JEE Main 2020 (Online) 9th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2020 (Online) 9th January Evening Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 4th September Morning Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 2nd September Morning Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 2nd September Evening Slot (4)
keyboard_arrow_right
JEE Main 2020 (Online) 3rd September Morning Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 3rd September Evening Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 4th September Evening Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 5th September Morning Slot (4)
keyboard_arrow_right
JEE Main 2020 (Online) 5th September Evening Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 6th September Morning Slot (1)
keyboard_arrow_right
JEE Main 2020 (Online) 6th September Evening Slot (4)
keyboard_arrow_right
JEE Main 2021 (Online) 24th February Morning Slot (3)
keyboard_arrow_right
JEE Main 2021 (Online) 25th February Evening Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 26th February Morning Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 26th February Evening Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 16th March Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 16th March Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 17th March Evening Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 18th March Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 20th July Morning Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 25th July Morning Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 25th July Evening Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 27th July Morning Shift (4)
keyboard_arrow_right
JEE Main 2021 (Online) 27th July Evening Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 26th August Morning Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 26th August Evening Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 27th August Morning Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 27th August Evening Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 31st August Morning Shift (1)
keyboard_arrow_right

EXAM MAP

Medical

NEET

Joint Entrance Examination

JEE Advanced JEE Main

Graduate Aptitude Test in Engineering

GATE CE GATE ECE GATE ME GATE IN GATE EE GATE CSE GATE PI