Magnetic Effect of Electric Current & Mechanical Effct of Electric Current
FSG_10_Magnetic Effect of Electric Current With Sol
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VERMA CLASSES, A-2/108; Mayur Apartments Sector-9; Rohn; !e" #e$h-11008%;&h' 011-2(%)9222; 9818988*(%+
Magnetic Effect of Electric Current
Electromagnetic Effect
Similar to other effects; electric current also producesmagnetic effect. The magnetic effect of electric current isknown as electromagnetic effect.It is observed that when a compass is brought near acurrent carrying conductor the needle of compass gets
deflected because of flow of electricity. This shows thatelectric current produces a magnetic effect.Properties of magnet:
A free suspended magnet always point towards
north and south direction.
The pole of a magnet which points toward northdirection is called north pole or north seeking.
The pole of a magnet which points toward south
direction is called south pole or south seeking.
Like poles of magnets repel each other while
unlike poles of magnets attract each other.
Magnetic field and Field Lines
The influence of force surrounding a magnet is calledmagnetic field. In the magnetic field, the force eerted bya magnet can be detected using a compass or any othermagnet.The imaginary lines of magnetic field around a magnet arecalled field line or field line of magnet. !hen iron fillings
are allowed to settle around a bar magnet, they getarranged in a pattern which mimicks the magnetic fieldlines. "ield line of a magnet can also be detected using acompass. #agnetic field is a vector $uantity, i.e. it hasboth direction and magnitude.%irection of "ield Line&' (utside the magnet, the direction
of magnetic field line is taken from north pole to South)ole. Inside the magnet, the direction of magnetic fieldline is taken from south pole to north pole.Strength of magnetic field& The closeness of field linesshows the relative strength of magnetic field, i.e. closerlines show stronger magnetic field and vice'versa.
*rowded field lines near the poles of magnet show more
strength.Magnetic field Due to a Current Carrying Conductor:
Magnetic field due to current through a straight
conductor:-
A current carrying straight conductor has magnetic field in
the form of concentric circles; around it. #agnetic field ofcurrent carrying straight conductor can be shown bymagnetic field lines.The direction of magnetic field through a current carryingconductor depends upon the direction of flow of electriccurrent. The direction of magnetic field gets reversed in
case of a change in the direction of electric current.Let a current carrying conductor be suspended vertically
and the electric current is flowing from south to north. Inthis case, the direction of magnetic field will be
anticlockwise. If the current is flowing from north tosouth, the direction of magnetic field will be clockwise.Right Hand Thum Rule: The direction of magneticfield; in relation to direction of electric current through astraight conductor can be depicted by using the +ightand Thumb +ule. It is also known as Ma!"ell#sCor$scre" Rule%
If a current carrying conductor is held by right hand;keeping the thumb straight and if the direction of electriccurrent is in the direction of thumb, then the direction ofwrapping of other fingers will show the direction ofmagnetic field.
As per #awell-s corkscrew rule, if the direction offorward movement of screw shows the direction ofcurrent, then the direction of rotation of screw shows thedirection of magnetic field.)roperties of #agnetic "ield&The magnitude; of magnetic field increases with increase
in electric current and decreases with decrease in electriccurrent.The magnitude of magnetic field; produced by electriccurrent; decreases with increase in distance and vice'versa.The sie of concentric circles of magnetic field linesincreases with distance from the conductor, which shows
that magnetic field decreases with distance.#agnetic field lines are always parallel to each other./o two field lines cross each other.#agnetic field due to current through a circular loop&In case of a circular current carrying conductor, themagnetic field is produced in the same manner as it is in
case of a straight current carrying conductor.In case of a circular current carrying conductor, themagnetic field lines would be in the form of concentriccircles around every part of the periphery of the conductor.Since, magnetic field lines tend to remain closer whennear the conductor, so the magnetic field would be
stronger near the periphery of the loop. (n the other hand,the magnetic field lines would be distant from each otherwhen we move towards the centre of the current carryingloop. "inally; at the centre, the arcs of big circles wouldappear as a straight lines.The direction of magnetic field can be identified using
+ight and Thumb-s +ule. Let us assume that the currentis moving in anti'clockwise direction in the loop. In thatcase, the magnetic field would be in clockwise direction;at the top of the loop. #oreover, it would be inanticlockwise direction at the bottom of the loop.
*lock "ace +ule&A current carrying loop works like a discmagnet. The polarity of this magnet can be easilyunderstood with the help of clock face rule. If the current
is flowing in anti'clockwise direction, then the face of theloop shows north pole. (n the other hand, if the current isflowing in clockwise direction, then the face of the loop
shows south pole.
G_10_General SciencePage 1
&ame: ''''''''''''''''' Class ( )u: '''''''''''''''Date: '''''' Remar$: '''''''
PR*CT+CE *))+,&ME&T
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#agnetic field and number of turns of coil&
#agnitude of magnetic field gets summed up withincrease in the number of turns of coil. If there are 0n-turns of coil, magnitude of magnetic field will be 0n- timesof magnetic field in case of a single turn of coil.#agnetic "ield due to a current in a Solenoid&
Solenoid is the coil with many circular turns of insulatedcopper wire wrapped closely in the shape of cylinder.A current carrying solenoid produces similar pattern ofmagnetic field as a bar magnet. (ne end of solenoidbehaves as the north pole and another end behaves as thesouth pole. #agnetic field lines are parallel inside thesolenoid; similar to a bar magnet; which shows that
magnetic field is same at all points inside the solenoid.1y producing a strong magnetic field inside the solenoid,magnetic materials can be magnetied. #agnet formed byproducing magnetic field inside a solenoid is calledelectromagnet.
Force on a current carrying conductor in a magnetic
field:A current carrying conductor eerts a force when a magnetis placed in its vicinity. Similarly, a magnet also eertse$ual and opposite force on the current carryingconductor. This was suggested by #arie Ampere, a "rench)hysicist and considered as founder of science of
electromagnetism.The direction of force over the conductor gets reversedwith the change in direction of flow of electric current. Itis observed that the magnitude of force is highest when thedirection of current is at right angles to the magnetic field.
Fleming#s Left Hand Rule:-
If direction of electric current is perpendicular to the
magnetic field, the direction of force is also perpendicularto both of them. The "leming-s Left and +ule states thatif the left hand is stretched in a way that the inde finger,the middle finger and the thumb are in mutuallyperpendicular directions; then the inde finger and middle
finger of a stretched left hand show the direction ofmagnetic field and direction of electric currentrespectively and the thumb shows the direction of motionor force acting on the conductor. The directions of electriccurrent, magnetic field and force are similar to threemutually perpendicular aes, i.e. , y and aes.
#any devices, such as electric motor, electric generator,loudspeaker, etc. works on the "leming-s left and +ule.
Electric Motor:-2lectrical energy is converted into mechanical energy byusing an electric motor. 2lectric motor works on the basisof rule suggested by #arie Ampere and "leming-s Left
and +ule.In an electric motor, a rectangular coil is suspendedbetween the two poles of a magnetic field. The electricsupply to the coil is connected with a commutator.*ommutator is a device which reverses the direction offlow of electric current through a circuit.
!hen electric current is supplied to the coil of electricmotor, it gets deflected because of magnetic field. As itreaches the half way, the split ring which acts as
commutator reverses the direction of flow of electriccurrent. +eversal of direction of current reverses the
direction of forces acting on the coil. The change in
direction of force pushes the coil; and it moves anotherhalf turn. Thus, the coil completes one rotation around theale. *ontinuation of this process keeps the motor inrotation.In commercial motor, electromagnet; instead of permanent
magnet; and armature is used. Armature is a soft iron corewith large number of conducting wire turns over it. Largenumber of turns of conducting wire enhances the magneticfield produced by armature.2lectromagnetic Induction#ichael "araday, an 2nglish )hysicist is supposed to havestudied the generation of electric current using magnetic
field and a conductor.!hen a conductor is set to move inside a magnetic field ora magnetic field is set to be changing around a conductor,electric current is induced in the conductor. This is 3ustopposite to the eertion of force by a current carryingconductor inside a magnetic field. In other words, when a
conductor is brought in relative motion vis'4'vis amagnetic field, a potential difference is induced in it. Thisis known as electromagnetic induction.2lectromagnetic induction can be eplained with the helpof "leming-s +ight and +ule. If the right hand isstretched in a way that the inde finger, middle finger and
thumb are in mutually perpendicular directions, then thethumb shows the direction of movement of the conductor,inde finger shows the direction of magnetic field and themiddle finger shows the direction of induced current in theconductor. The directions of movement of conductor,magnetic field and induced current can be compared to
three mutually perpendicular aes, i.e. , y and aes.
The mutually perpendicular directions also point to animportant fact that the when the magnetic field andmovement of conductor are perpendicular, the magnitudeof induced current would be maimum.2lectromagnetic induction is used in the conversion of
kinetic energy into electrical energy.2lectric generator&The structure of electric generator is similar to that of anelectric motor. In case of an electric generator arectangular armature is placed within the magnetic field ofa permanent magnet. The armature is attached to wire and
is positioned in way that it can move around an ale.!hen the armature moves within the magnetic field an
electric current is induced. The direction of inducedcurrent changes, when the armature crosses the halfwaymark of its rotation. Thus, the direction of current changesonce in every rotation. %ue to this, the electric generator
usually produces alternate current, i.e. A*. To convert anA* generator into a %* generator, a split ring commutatoris used. This helps in producing direct current.A* and %* current&A* 5 Alternate current&' *urrent in which direction ischanged periodically is called Alternate *urrent. In India,
most of the power stations generate alternate current. Thedirection of current changes after every 67688 second inIndia, i.e. the fre$uency of A* in India is 98 . A* is
transmitted upto a long distance without much loss ofenergy is advantage of A* over %*.
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%* 5 %irect current&'*urrent that flows in one direction
only is called %irect current. 2lectrochemical cellsproduce direct current.
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NCERT Solutions
)olution of +n Te!t uestions - part - .
:uestion& 6 ' !hy does a compass needle get deflected when
brought near a bar magnet
Answer& !hen a compass needle is brought near a bar magnet,the compass needle eperiences a deflection. This happens
because of interaction of magnetic fields of the compass needle
and the bar magnet.
:uestion& < ' %raw magnetic field lines around a bar magnet.
Answer&
:uestion& = &' List the properties of magnetic lines of force.
Answer& )roperties of magnetic field lines&
a. #agnetic field lines follow the direction from the north
pole to the south pole.
b. #agnetic field lines always show concentric pattern.
c. #agnetic field lines do not cross one another.
d. *loser the field lines; stronger is the magnetic field and
vice'versa is also true.
e. #agnetic field lines are closer near the poles; which
shows greater strength of magnetic field near the poles.
:uestion& > &' !hy don-t two magnetic lines of force intersect
each other
Answer& The direction of magnetic field lines is always from the
north pole to the south pole. If the field lines would cross each
other then the direction of field line would change at the point of
crossing which is practically impossible. ence, two magneticfield lines never intersect each other.
:uestion& 9 &' *onsider a circular loop of wire lying in the plane
of the table. Let the current pass through the loop clockwise.
Apply the right hand rule to find out the direction of the
magnetic field inside and outside the loop.
Answer& As the given figure shows; current is flowing clockwisethrough a circular loop. The direction of magnetic field around
the conductor can be known by using the right hand thumb rule.
As the figure shows, the magnetic field would be towards the
plane of the paper when it is inside the loop. (n the other hand,
the magnetic field would be away from the paper when it is
outside the loop.
:uestion& ? &' The magnetic field in a given region is uniform.
%raw a diagram to represent it.
Answer&
:uestion& @ &' *hoose the correct option.
The magnetic field inside a long straight solenoid'carrying
current
a. Is ero.
b. %ecreases as we move towards its end.
c. Increases as we move towards its end.
d. Is the same at all points.
Answer& dB Is the same at all points.
:uestion& C &' !hich of the following property of a proton can
change while it moves freely in a magnetic field There may be
more than one correct answerB
a. #assb. Speed
c. Delocity
d. #omentum
Answer& cB and dB, i.e. velocity and mass of proton changewhen it enters a magnetic field. !hen a proton enters a magnetic
field it starts moving on a circular path. 1ecause of its movement
along a circular path it attains angular momentum. !e know that
momentum is a product of mass and velocity.
:uestion& E ' In Activity 6=.@, how do we think the displacement
of rod A1 will be affected if iB current in rod A1 is increased;
iiB a stronger horse'shoe magnet is used; and iiiB length of therod A1 is increased
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Answer& In this case, the displacement would vary directly as the
strength of current, strength of magnetic field and length of theconductor. %ue to this, the displacement of conductor would be
increased in all the three cases.
NCERT Solutions
)olution of +n Te!t uestions - part - /
:uestion& 68 ' A positively'charged particle alpha'particleB
pro3ected towards west is deflected towards north by a magnetic
field. The direction of magnetic field is
a. Towards south
b. Towards east
c. %ownward
d. Fpward
Answer&' This $uestion can be solved by using "leming-s Left
and +ule. !e know that the direction of current is opposite to
the direction of electron-s movement and hence it would be sameas the direction of proton-s movement. So, the direction of
current is towards west. As per "leming-s Left and +ule; the
middle finger shows the direction of current, the forefinger
shows the direction of magnetic field and the thumb shows the
direction of motion. ere, the deflection is towards north, i.e. in
north westerly direction and hence, the direction of magneticfield would be towards north, i.e. upward.
:uestion& 66 &' State "leming-s Left and +ule.
Answer& "leming-s Left and +ule states that if the left hand isstretched in a way that the inde finger, the middle finger and the
thumb are in mutually perpendicular directions; then the inde
finger and middle finger of a stretched left hand show the
direction of magnetic field and direction of electric currentrespectively and the thumb shows the direction of motion or
force acting on the conductor. The directions of electric current,
magnetic field and force are similar to three mutually
perpendicular aes, i.e. , y and aes.
:uestion& 6< &' !hat is the principle of an electric motor
Answer& )rinciple of 2lectric #otor& The electric motor works
on the principle of "leming-s Left and +ule. !hen arectangular coil is placed within a magnetic field and current is
passed through the coil, there is deflection in the coil. The
deflection changes into rotation of coil because of split ring
commutator in the motor.
:uestion& 6= &' !hat is the role of a split ring in an electric
motor
Answer& In an electric motor, after every half rotation the
direction of coil gets reversed due to change in orientation of themagnetic field. To ensure a continuous rotation; a split ring is
attached to the coil so that the polarity of the coil changes after
every half rotation. This changes the direction of current and thus
the armature keeps on rotating continuously.
:uestion& 6> ' 2plain different ways to induce current in a coil.
Answer& "or electromagnetic induction; the coil and the magnet
should be in relative motion. This can be ensured by any of thefollowing two ways&
a. The coil should be moved within a magnetic field.b. The magnet should be moved and coil can be kept
static.
:uestion& 69 ' State the principle of an electric generator.
Answer& 2lectric Generator works on the principle of
electromagnetic induction which obeys "leming-s +ight and
+ule. !hen coil is moved inside a magnetic field a current isinduced in the coil. The electric current is thus 0generated- by
electric generator.
:uestion& 6? ' /ame some sources of direct current.
Answer& 2lectrochemical cell, %* generator, photovoltaic cell,
etc.
:uestion& 6@ ' !hich sources produce alternating current
Answer& A* generator
:uestion& 6C ' *hoose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field.
The direction of the induced current changes once in each
a. two revolutionsb. one revolution
c. half revolution
d. one'fourth revolution
Answer& cB alf revolution
:uestion& 6E ' /ame two safety measures commonly used inelectric circuits and appliances.
Answer& 2arth wire and electric fuse
:uestion&
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ere, the oven is drawing E.8E ampere of current from a 9
ampere source.
This means there would be an overload on the circuit. This canresult in accidental fire in the circuit.
:uestion&
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between different poles of two magnets. If the north pole of the
bar magnet gets repulsed by a particular pole of theelectromagnet solenoidB then it gets confirmed that the bar
magnet was brought near the north pole of the electromagnet.
:uestion& E ' !hen is the force eperienced by a current5
carrying conductor placed in a magnetic field largest
Answer& "rom "leming-s Left and +ule, it is clear that when
the direction of current and magnetic field are in mutually
perpendicular directions, the deflection in conductor is the
maimum. This shows that when magnetic field and direction ofcurrent are perpendicular to each other, the force eperienced by
the conductor is the largest.
:uestion& 68 ' Imagine that you are sitting in a chamber with
your back to one wall. An electron beam, moving horiontally
from back wall towards the front wall, is deflected by a strong
magnetic field to your right side. !hat is the direction ofmagnetic field
Answer& ere, the electron beam is moving towards the viewer,
i.e. out of the plane of the page. This means that the direction of
current is towards the page. This shows the direction in which
the forefinger is pointing. The thumb is pointing towards right
which is same as the direction of deflection. The middle finger is
pointing downwards; which shows the direction of the magneticfield.
:uestion& 66 ' %raw a labelled diagram of an electric motor.
2plain its principle and working. !hat is the function of a split
ring in an electric motor
Answer&'
.
!orking of 2lectric #otor&
2lectrical energy is converted into mechanical energy by using
an electric motor. 2lectric motor works on the basis of rule
suggested by #arie Ampere and "leming-s Left and +ule.
In an electric motor, a rectangular coil is suspended between the
two poles of a magnetic field. The electric supply to the coil isconnected with a commutator. *ommutator is a device which
reverses the direction of flow of electric current through a circuit.
!hen electric current is supplied to the coil of electric motor, it
gets deflected because of magnetic field. As it reaches the half
way, the split ring which acts as commutator reverses the
direction of flow of electric current. +eversal of direction of
current reverses the direction of forces acting on the coil. Thechange in direction of force pushes the coil; and it moves another
half turn. Thus, the coil completes one rotation around the ale.
*ontinuation of this process keeps the motor in rotation.
In commercial motor, electromagnet; instead of permanent
magnet; and armature is used. Armature is a soft iron core withlarge number of conducting wire turns over it. Large number ofturns of conducting wire enhances the magnetic field produced
by armature.
:uestion& 6< &' /ame some devices in which electric motors are
used.
Answer& 2lectric fan, mier grinder, tape recorder, *% player,
hard disk drive, washing machine, cooler, toy car, vacuum
cleaner, etc. are some devices in which electric motor is used.
:uestion& 6= &' A coil of insulated copper wire is connected to a
galvanometer. !hat will happen if a bar magnet is iB pushedinto the coil, iiB withdrawn from inside the coil, iiiB held
stationary inside the coil
Answer& !hen the bar magnet is pushed into the coil or
withdrawn from the coil; the galvanometer needle would show
deflection. !hen the bar magnet is kept stationary inside the
coil; the galvanometer needle would show no deflection.
:uestion& 6> &' Two circular coils A and 1 are placed close toeach other. If the current in the coil A is changed, will some
current be induced in the coil 1 Give reason.
Answer& !hen two circular coils A and 1 are placed close to
each other and the current in coil A is changed, it leads to
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induction of current in coil 1. This happens because of change in
magnetic field of coil A; because of change in current in this coil.
:uestion& 69 &' State the rule to determine the direction of a iBmagnetic field produced around a straight conductor'carrying
current, iiB force eperienced by a current'carrying straight
conductor placed in a magnetic field which is perpendicular to it,and iiiB current induced in a coil due to its rotation in a magnetic
field.
Answer&
i. +ight hand thumb rule or #awell-s corkscrew rule,ii. "leming-s Left and +ule and
iii. "leming-s +ight and +ule
:uestion& 6? ' 2plain the underlying principle and working of
an electric generator by drawing a labelled diagram. !hat is the
function of brushes
Answer&
The structure of electric generator is similar to that of an electric
motor. In case of an electric generator a rectangular armature is
placed within the magnetic field of a permanent magnet. Thearmature is attached to wire and is positioned in way that it can
move around an ale. !hen the armature moves within the
magnetic field an electric current is induced.
The direction of induced current changes, when the armature
crosses the halfway mark of its rotation. Thus, the direction of
current changes once in every rotation. %ue to this, the electric
generator usually produces alternate current, i.e. A*.
To convert an A* generator into a %* generator, a split ringcommutator is used. This helps in producing direct current.
:uestion& 6@ ' !hen does an electric short circuit occur
Answer& !hen positive and negative wires touch each other, the
resistance suddenly decreases and current increases. This leads to
ecessive heating of wire which manifests in the form of sparks.
This is called short circuit.
:uestion& 6C ' !hat is the function of an earth wire !hy is it
necessary to earth metallic appliances
Answer& The earth wire transfers any leakage of electric currentto the earth. The leaked current can otherwise reach the metallic
body of an appliance and can lead to electric shock. 2arth wire
prevents from electric shock by safety transferring the leakedcurrent to the earth.
Exemplar Problem and Solution (NCERT)
E!emplar )olution - MC
:uestion& 6 &' *hoose the incorrect statement from the following
regarding magnetic lines of field
a. The direction of magnetic field at a point is taken to bethe direction in which the north pole of a magnetic
compass needle points
b. #agnetic field lines are closed curves
c. If magnetic field lines are parallel and e$uidistant, they
represent ero field strength
d. +elative strength of magnetic field is shown by the
degree of closeness of the field lines
Answer&' cB If magnetic field lines are parallel and e$uidistant,
they represent ero field strength
:uestion& < &' If the key in the arrangement "igure 6=.6B is taken
out the circuit is made openB and magnetic field lines are drawnover the horiontal plane A1*%, the lines are
a. *oncentric circlesb. 2lliptical in shape
c. Straight lines parallel to each other
d. *oncentric circles near the point ( but of ellipticalshapes as we go away from it
Answer&' aB *oncentric circles
:uestion& = ' A circular loop placed in a plane perpendicular to
the plane of paper carries a current when the key is (/. The
current as seen from points A and 1 in the plane of paper and on
the ais of the coilB is anti clockwise and clockwise respectively.
The magnetic field lines point from 1 to A. The /'pole of theresultant magnet is on the face close to
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a. A
b. 1
c. A if the current is small, and 1 if the current is large
d. 1 if the current is small and A if the current is large
Answer&' aB A
:uestion& > ' "or a current in a long straight solenoid /' and S'
poles are created at the two ends. Among the following
statements, the incorrect statement is
a. The field lines inside the solenoid are in the form of
straight lines which indicates that the magnetic field is
the same at all points inside the solenoid
b. The strong magnetic field produced inside the solenoid
can be used to magnetise a piece of magnetic material
like soft iron, when placed inside the coil
c. The pattern of the magnetic field associated with the
solenoid is different from the pattern of the magnetic
field around a bar magnet
d. The /' and S'poles echange position when thedirection of current through the solenoid is reversed
Answer& cB The pattern of the magnetic field associated with the
solenoid is different from the pattern of the magnetic field
around a bar magnet
:uestion& 9 &' *ommercial electric motors do not use
a. An electromagnet to rotate the armature
b. 2ffectively large number of turns of conducting wire in
the current carrying coil
c. A permanent magnet to rotate the armature
d. A soft iron core on which the coil is wound
Answer& cB A permanent magnet to rotate the armature
:uestion& ? &' A uniform magnetic field eists in the plane ofpaper pointing from left to right as shown in "igure 6=.=. In the
field an electron and a proton move as shown. The electron and
the proton eperience
a. "orces both pointing into the plane of paper
b. "orces both pointing out of the plane of paper
c. "orces pointing into the plane of paper and out of the
plane of paper, respectively
d. "orce pointing opposite and along the direction of the
uniform magnetic field respectively
Answer& cB "orces pointing into the plane of paper and out ofthe plane of paper, respectively
:uestion& @ &' In the arrangement shown in "igure 6=.> there are
two coils wound on a non'conducting cylindrical rod. Initially
the key is not inserted. Then the key is inserted and later
removed. Then
a. The deflection in the galvanometer remains ero
throughout
b. There is a momentary deflection in the galvanometer
but it dies out shortly and there is no effect when thekey is removed
c. There are momentary galvanometer deflections that die
out shortly; the deflections are in the same direction
d. There are momentary galvanometer deflections that die
out shortly; the deflections are in opposite directions
Answer& cB There are momentary galvanometer deflections that
die out shortly; the deflections are in the same direction
:uestion& C' *hoose the incorrect statement
a. "leming-s right'hand rule is a simple rule to know the
direction of induced current
b. The right'hand thumb rule is used to find the direction
of magnetic fields due to current carrying conductors
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c. The difference between the direct and alternating
currents is that the direct current always flows in onedirection, whereas the alternating current reverses its
direction periodically
d. In India, the A* changes direction after every 6798
second
Answer& dB In India, the A* changes direction after every 6798
second
:uestion& E ' A constant current flows in a horiontal wire in the
plane of the paper from east to west as shown in "igure 6=.9. The
direction of magnetic field at a point will be /orth to South
a. %irectly above the wireb. %irectly below the wire
c. At a point located in the plane of the paper, on the
north side of the wire
d. At a point located in the plane of the paper, on thesouth side of the wire
Answer& aB %irectly above the wire
:uestion& 68' The strength of magnetic field inside a long
current carrying straight solenoid is
a. #ore at the ends than at the centre
b. #inimum in the middle
c. Same at all points
d. "ound to increase from one end to the other
Answer& cB Same at all points
:uestion& 66 ' To convert an A* generator into %* generator
a. Split'ring type commutator must be used
b. Slip rings and brushes must be used
c. A stronger magnetic field has to be used
d. A rectangular wire loop has to be used
Answer& aB Split ring type commutator must be used
:uestion& 6
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:uestion& 69 &' A1 is a current carrying conductor in the plane of
the paper as shown in "igure 6=.@. !hat are the directions ofmagnetic fields produced by it at points ) and : Given r6 H r
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:uestion&
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1ased on above observations, it can be said that when a current
carrying conductor is placed within a magnetic field; theconductor eperiences deflection. "leming-s Left and +ule
eplains the direction of displacement in this case. Let us assume
that the current is moving in anti'clockwise direction in the loop.
In that case, the magnetic field would be in clockwise direction;
at the top of the loop. #oreover, it would be in anticlockwise
direction at the bottom of the loop.
:uestion&
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The structure of electric generator is similar to that of an electric
motor. In case of an electric generator a rectangular armature isplaced within the magnetic field of a permanent magnet. The
armature is attached to wire and is positioned in way that it canmove around an ale. !hen the armature moves within the
magnetic field an electric current is induced.
The direction of induced current changes, when the armature
crosses the halfway mark of its rotation. Thus, the direction of
current changes once in every rotation. %ue to this, the electricgenerator usually produces alternate current, i.e. A*.
To convert an A* generator into a %* generator, a split ring
commutator is used. This helps in producing direct current.
:uestion& =< ' %raw an appropriate schematic diagram showing
common domestic circuits and discuss the importance of fuse.!hy is it that a burnt out fuse should be replaced by another fuse
of identical rating
Answer&
Importance of "use& The electric fuse is an important device in
household wiring and also in many electrical appliances. 1y
melting, the fuse wire breaks the circuit and thus helps in saving
the wiring or the appliance from damage.
A fuse wire works because of its lower melting point which is
possible because of its respective rating. If a fuse with larger
rating is used with an appliance, the fuse wire shall not melt andhence would fail to serve the re$uired purpose. %ue to this, a
fuse with defined rating should not be replaced by one with a
larger rating.
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