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Magnetic field lines due to current - class-XI

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In a circular current-carrying conductor, if the current flows in the clockwise direction, the magnetic field direction is __________.

  1. Parallel to the coil towards the observer

  2. Perpendicular to the plane of the coil away from the observer

  3. Perpendicular to the plane of the coil towards the observer

  4. Parallel to the plane of the coil away from the observer


Correct Option: B
Explanation:

The magnetic field are concentric circle at point of a current carrying circular conductor direction of the magnetic field of every section of the circular loop can be found by using the right hand thumb rule .if you curl your right hand fingers in direction of magnetic field your thumb will point in the direction of the current flow.

Consider an experiment where Electric current is flowing in a wire. It is observed that clockwise magnetic field is produced around the wire. A teacher decides to reverse the direction of source battery which results in reversal of electrical current. What will be the effect on magnetic field?

  1. Magnetic field disappears

  2. Direction of field lines reverse

  3. Field lines changes direction to parallel to wire

  4. None of the above


Correct Option: B
Explanation:

Using Right Hand thumb rule, as current direction reverses, you need to reverse the hand and direction of magnetic field reverses.

Axis of a solid cylinder of infinite length and radius $R$ lies along $y$-axis. It carries a uniformly distributed corrent I along +$y$ direction. Magnetic field at a point $(R/2,y,R/2)$ is 

  1. $\cfrac{\mu _{0}I}{4\pi R}\left(\hat{i}-\hat{k}\right)$

  2. $\cfrac{\mu _{0}I}{2\pi R}\left(\hat{j}-\hat{k}\right)$

  3. $\cfrac{\mu _{0}I}{4\pi R}\hat{j}$

  4. $\cfrac{\mu _{0}I}{4\pi R}\left(\hat{j}+\hat{k}\right)$


Correct Option: A

A current carrying circular loop of radius R is placed in the x-y plane with centre at the origin. Half of the loop with x > 0 is now bent so that it now lies in the $y-z$ plane.

  1. The magnitude of magnetic moment now diminishes.

  2. The magnetic moment does not change.

  3. The magnitude of $\bar B$ at $(0,0, z), z$>>R increases.

  4. The magnitude of $\bar B$ at $(0, 0, z), z$>>R is unchanged.


Correct Option: A
Explanation:

For a circular loop of radius R carrying current, I placed in $x-y$ plane, the magnetic moment $M= I\,\,\pi R^2$. It acts perpendicular to the loop i.e., along with the z-direction. When half of the current loop is bent in y-z plane, the magnetic moment due to half current loop in x-y plane,$ M _1 = I \left (\dfrac {\pi R^2}{2} \right )$ acting along z-direction.
Magnetic moment due to half current loop in y-z plane,$ M _2 = I \left (\dfrac {\pi R^2}{2} \right )$ along x-direction.
Effective magnetic moment due to entire bent current loop,
$M'$ =$\sqrt{{M _{1}^{2}}+ {M _{2}^{2}}} $=$\sqrt {{\left (\dfrac{I \pi R^2}{2} \right )^2}+{\left (\dfrac{I \pi R^2}{2} \right )^2}}$
$M'=\dfrac{I\pi R^2}{2}\sqrt2 <M$
i.e., magnetic moment diminishes.

Why does toroid have a higher magnetic field than a solenoid?

  1. It is magnetically efficient.

  2. It is a straight core.

  3. It has an open loop core.

  4. It has a closed loop core.


Correct Option: D
Explanation:
Due to the symmetry and being closed loop core.
Totoid has higher magnetic field and thus higher inductor and Q-facator

Which among the following is not an electronic component used in constructing a toroid?

  1. copper wires

  2. laminated iron

  3. ferrite core

  4. aluminium powder


Correct Option: D
Explanation:
Toroids are inductors and transformers which use magnetic cores.
These cores are of ferromagnetic material such as
Laminated iron, iron powder or ferrite.

The leakage flux of a toroid is less because

  1. It is asymmetrical.

  2. It has an open-loop core.

  3. It is symmetrical.

  4. It has a straight core.


Correct Option: C
Explanation:
Toroidal is a surface of revolution with hole in middle.
This is a solid body used for toroid production.
The advantage of this shape is that, due to its symmetry amount of magnetic flux that escapes outside is low.

Which of the following is true for a toroid?

  1. low inductance and Q factor

  2. high inductance and Q factor

  3. high inductance and low Q-factor

  4. low inductance and high Q-factor


Correct Option: B
Explanation:

Due to the symmetry and being closed loop core.
Toroid has higher magnetic field and thus higher inductor and Q-factor

A toroid is                  solenoid

  1. a finite

  2. an endless

  3. straight

  4. either A or B


Correct Option: B
Explanation:

A Toroid is a solenoid which is bent in the form of a ring with its both the ends joined together.  Since both the ends are merged, it appears endless.

A solenoid of length 0.4 m, having 500 turns and 3A current flows through it. A coil of radius 0.01 m and have 10 turns and carries current of 0.4 A has to placed such that its axis is perpendicular to the axis of solenoid ,then torque on coil will be

  1. $5.92\times 10^{-7} N.m$

  2. $5.92\times 10^{-5} N.m$

  3. $5.92\times 10^{-4} N.m$

  4. $5.92\times 10^{-3} N.m$


Correct Option: A
Explanation:
Magnetic field due to larges solenoid
$B=\dfrac {\mu _{0} NI}{l}=\dfrac {4\times 10^{-7}\times 500 \times 3}{0.4}$
$N=500$ 
$I=3$
$l=0.4$
Torque $M$ solenoid $I\times $ Area of corn section $\times B$
$=0.4\times \pi 0.01^{2}\times 4\pi \times \dfrac{10^{-7}\times 500 \times 3}{0.4}$
 orque $=\pi.0.01^{2} \times 4\pi \times 10^{-7}\times 500 \times 3$
Torque $=5.92\times 10^{-7}N-m$

Which of the following entities are closely associated to each other

  1. Gravitation and nuclear fusion

  2. Electricity and magnetism

  3. Chemical Bonding and Planetary motion

  4. None


Correct Option: B
Explanation:

Electric current and magnetism are very closely related phenomenon and both can be generated using the other.

Define Electromagnetism

  1. The study of attraction or repulsion between two magnets is called electromagnetism

  2. The study of electric effects due to magnetic interaction is called electromagnetism

  3. The study of magnetic effects produced due to electric current is called electromagnetism

  4. The study of magnetic effects produced due to electric charge is called electromagnetism


Correct Option: C
Explanation:

Electromagnetism is study of various phenomenon related to electricity and magnetism. 

Which of the following phenomenon can be related to electric current 

  1. Magentism

  2. Gravitation

  3. Nuclear Fission

  4. Chemical Bonding


Correct Option: A
Explanation:

Electric current and magnetism are very closely related phenomenon and both can be generated using the other.

The Magnetic effect of current was discovered by:

  1. John Ambrose Fleming

  2. Hans Christian Oersted

  3. Michael Faraday

  4. André-Marie Ampère


Correct Option: B
Explanation:
The magnetic effect of an electric current was discovered by Hans Christian Oersted in 1820. He demonstrated the effect by plotting compass close to a long straight wire which is carrying current and noting it's deflection. And the by reversing the direction of the current, the compass needle was deflected in the opposite sense.

How can you determine direction of magnetic field lines around a current carrying conductor

  1. Left hand Thumb Rule

  2. Right Hand Thumb Rule

  3. By rotating the conductor

  4. Using sonometer


Correct Option: B
Explanation:

Direction of magnetic field lines around a current carrying conductor can be found by RIght Hand Thumb Rule.

One metal wire is kept in east-west direction.  $I$  is the current flow due west. Then, due to magnetic field  $\vec { { B } }$  of the earth on the wire is in the........ Direction.

  1. downward

  2. Upward

  3. north

  4. south


Correct Option: C
Explanation:
according to left hand rule. if current is in west direction then magnetic field will be north direction, if force is in north west direction

The shape of a magnetic field lines around a straight current carrying conductor is.......

  1. Circular

  2. Straight line

  3. Curved

  4. Parabolic


Correct Option: A
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