1
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

An infinitely long current carrying wire and a small current carrying loop are in the plane of the paper as shown. The radius of the loop is a and distance of its centre from the wire is d (d > > a). If the loop a applies a force F on the wire then :

A
$$F = 0$$
B
$$F \propto \left( {{a \over d}} \right)$$
C
$$F \propto \left( {{{{a^2}} \over {{d^3}}}} \right)$$
D
$$F \propto {\left( {{a \over d}} \right)^2}$$

Explanation

Magnetic field due to current carrying loop at distance d, is,

B = $${{{\mu _0}} \over {4\pi }} \times {{\overrightarrow M \times \overrightarrow d } \over {{d^3}}}$$

= $${{{\mu _0}} \over {4\pi }} \times {{i \times \pi {a^2} \times d \times \sin {{90}^o}} \over {{d^3}}}$$   [as  M = iA]

= $${{{\mu _0}} \over {4\pi }} \times {{i\pi {a^2}} \over {{d^2}}}$$

$$ \therefore $$   B $$ \propto $$ $${{{a^2}} \over {{d^2}}}$$

We also know,

F = Bil

$$ \therefore $$   F $$ \propto $$ B

So, F $$ \propto $$ $${{{a^2}} \over {{d^2}}}$$
2
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

A plane electromagnetic wave of frequency 50 MHz travels in free space along the positive x-direction. At a particular point in space and time, $$\overrightarrow E = 63\widehat j\,V/m.$$ The corresponding magnetic field $$\overrightarrow {B,} $$ at that point will be :
A
18.9 $$ \times $$ 10$$-$$8 $$\widehat k$$T
B
2.1 $$ \times $$ 10$$-$$8 $$\widehat k$$T
C
6.3 $$ \times $$ 10$$-$$8 $$\widehat k$$T
D
18.9 $$ \times $$ 108 $$\widehat k$$T

Explanation

Given, $$\overrightarrow E = 6.3\widehat j$$

$$ \therefore $$   $$\left| {\overrightarrow E } \right| = \sqrt {{{\left( {6.3} \right)}^2}} = 6.3$$

$$ \therefore $$   $$\left| {\overrightarrow B } \right| = {{\left| {\overrightarrow E } \right|} \over C}$$

$$ = {{6.3} \over {3 \times {{10}^8}}}$$

$$ = 2.1 \times {10^{ - 8}}\,$$ T

Now we have to find the direction of $$\overrightarrow B $$.

We know, $$\widehat E \times \widehat B = \widehat C$$ and given $$\overrightarrow E $$ is in y-direction and wave moving in positive x-direction.

$$ \therefore $$   $$\widehat J \times \widehat B = \widehat i$$

$$ \Rightarrow $$   $$\widehat B = \widehat K$$

$$ \therefore $$   $$\overrightarrow B = \left| {\overrightarrow B } \right|\widehat B$$

$$ = 2.1 \times {10^{ - 8}}\,\widehat K\,T$$
3
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Morning Slot

A bar magnet is demagnetized by inserting it inside a solenoid of length 0.2 m, 100 turns, and carrying a current of 5.2 m, 100 turns, and carrying a current of 5.2 A. The corecivity of the bar magnet is :
A
285 A/m
B
2600 A/m
C
520 A/m
D
1200 A/m

Explanation

Coercivity, H = $${B \over {{\mu _0}}}$$

Inside solenoid the magnetic field,

B = $$\mu $$0ni

$$ \therefore $$   H = $${{{\mu _0}ni} \over {{\mu _0}}}$$

= ni

= $${N \over \ell } \times i$$

= $${{100} \over {0.2}} \times 5.2$$

= 2600 A/m
4
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Evening Slot

The energy associated with electric field is (UE) and with magnetic field is (UB) for an electromagnetic wave in free space. Then :
A
$${U_E} = {{{U_B}} \over 2}$$
B
$${U_E} > {U_B}$$
C
$${U_E} < {U_B}$$
D
$${U_E} = {U_B}$$

Explanation

Energy density of magnetic field (UB) = $${{{B^2}} \over {2{\mu _0}}}$$

Also,

Energy density of electric field

UE = $${1 \over 2}$$ $$\varepsilon $$0E2

= $${1 \over 2}$$ $$\varepsilon $$0 B2 C2     [as   $${E \over B}$$ = C ]

= $${1 \over 2}$$ $$\varepsilon $$0 B2 $$ \times $$ $$\left( {{1 \over {{\varepsilon _0}{\mu _0}}}} \right)$$    [as   C2 = $${{1 \over {{\varepsilon _0}{\mu _0}}}}$$]

= $${{{B^2}} \over {2{\mu _0}}}$$

$$ \therefore $$  UB = UE

Questions Asked from Magnetics

On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Name Indicates No of Questions
AIEEE 2002 (4)
keyboard_arrow_right
AIEEE 2003 (5)
keyboard_arrow_right
AIEEE 2004 (7)
keyboard_arrow_right
AIEEE 2005 (5)
keyboard_arrow_right
AIEEE 2006 (3)
keyboard_arrow_right
AIEEE 2007 (5)
keyboard_arrow_right
AIEEE 2008 (2)
keyboard_arrow_right
AIEEE 2009 (2)
keyboard_arrow_right
AIEEE 2010 (1)
keyboard_arrow_right
AIEEE 2011 (1)
keyboard_arrow_right
AIEEE 2012 (2)
keyboard_arrow_right
JEE Main 2013 (Offline) (1)
keyboard_arrow_right
JEE Main 2014 (Offline) (2)
keyboard_arrow_right
JEE Main 2015 (Offline) (2)
keyboard_arrow_right
JEE Main 2016 (Offline) (3)
keyboard_arrow_right
JEE Main 2016 (Online) 9th April Morning Slot (3)
keyboard_arrow_right
JEE Main 2016 (Online) 10th April Morning Slot (3)
keyboard_arrow_right
JEE Main 2017 (Offline) (2)
keyboard_arrow_right
JEE Main 2017 (Online) 8th April Morning Slot (3)
keyboard_arrow_right
JEE Main 2017 (Online) 9th April Morning Slot (2)
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 (1)
keyboard_arrow_right
JEE Main 2018 (Online) 16th April Morning Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 9th January Morning Slot (5)
keyboard_arrow_right
JEE Main 2019 (Online) 9th January Evening Slot (3)
keyboard_arrow_right
JEE Main 2019 (Online) 10th January Morning Slot (3)
keyboard_arrow_right
JEE Main 2019 (Online) 10th January Evening Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 11th January Morning Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 11th January Evening Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 12th January Morning Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 12th January Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 8th April Morning Slot (3)
keyboard_arrow_right
JEE Main 2019 (Online) 8th April Evening Slot (3)
keyboard_arrow_right
JEE Main 2019 (Online) 9th April Morning Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 9th April Evening Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 10th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 10th April Evening Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 12th April Morning Slot (4)
keyboard_arrow_right
JEE Main 2019 (Online) 12th April Evening Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 7th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2020 (Online) 7th January Evening Slot (4)
keyboard_arrow_right
JEE Main 2020 (Online) 8th January Morning Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 8th January Evening Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 9th January Morning Slot (3)
keyboard_arrow_right
JEE Main 2020 (Online) 9th January Evening Slot (2)
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 (2)
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 (2)
keyboard_arrow_right
JEE Main 2020 (Online) 5th September Evening Slot (4)
keyboard_arrow_right
JEE Main 2020 (Online) 6th September Morning Slot (2)
keyboard_arrow_right
JEE Main 2020 (Online) 6th September Evening Slot (3)
keyboard_arrow_right
JEE Main 2021 (Online) 24th February Evening Slot (1)
keyboard_arrow_right
JEE Main 2021 (Online) 25th February Morning Slot (2)
keyboard_arrow_right
JEE Main 2021 (Online) 25th February Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 26th February Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 16th March Morning Shift (4)
keyboard_arrow_right
JEE Main 2021 (Online) 16th March Evening Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 17th March Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 17th March Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 18th March Morning Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 18th March Evening Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 20th July Morning Shift (2)
keyboard_arrow_right
JEE Main 2021 (Online) 20th July Evening Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 22th July Evening Shift (3)
keyboard_arrow_right
JEE Main 2021 (Online) 25th July Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 25th July Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 27th July Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 26th August Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 26th August Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 27th August Morning Shift (2)
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
JEE Main 2021 (Online) 31st August Evening Shift (3)
keyboard_arrow_right

EXAM MAP

Joint Entrance Examination

JEE Advanced JEE Main

Medical

NEET

Graduate Aptitude Test in Engineering

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