MA$N%T' %%'T '*++%NT
(A) Permanent (atural ! Artificial magnets) (") Temporary (#lectromagnets) (A) Permanent (Natural & Artificial magnets) Natural magnets
Definition : Pieces of naturally occurring iron
ore lode$s lode$sto tone ne or magne magnetic tic or blac% blac% iron iron o&ide ('e*), are called natural magnets.
Thesee have have foll follow owin ing g two two Prope operti rties : Thes properties.
(i) Attrac Attracti tive ve proper property+ ty+ They They attra attract ct small small iron iron pieces towards them. them. (ii) irectiv irectivee property+ property+ -hen suspended suspended freely freely,, their ends would point in geographical north$ sout south h dir directi ectio on. 'or 'or thi this reaso eason, n, the susp suspen ende ded d piec piecee is call called ed lode lode ston stonee or leading stone.
Disadant Disadantage age : These These have following following two
demerits + (i) They have have irregu irregular lar shape. shape. (ii) They are wea%.
These magne magnets ts are made made of Description : These thes thesee magn magnet etss have have many many smal smalll !atomic" magnets. rdinarily they are all oriented in
called magnetism.
random directions ('ig.). Then the substance
The substance having property of magnetism,
is unmagnetised.
is called magnet.
Types of Magnets CAREER POINT #
Artificial Magnets
hard steel or special alloys. The substances of
Magne Magnetis tism m : The property due to which a
substance attracts iron pieces towards it, is
(a) nmagnetised
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The streng strength th of a perma permanen nentt 0treng 0tr engt t : The magnet cannot be changed. (b) agnetised. -hen -hen such such a piece piece is put in orth orth$;o $;outh uth
direction and hammered, the atomic magnets
are dipped in iron filings, the filings stic% to
align themselves in the direction of the earth
its ends only and not to its sides. t means that
field fig. They retain this alignment and the piece becomes a magnet with orth () and
in magnets, centres of attraction are located
(;) pole near near ends. ends. This magne magnett with with two
near ends only. only. These These centres centres of attractio attraction n
poles, is called a magnetic dipole.
Poles Poles of a magnet : -hen ends of a magnet
near the ends of a magnet are called poles.
Adan Adantag tagee : Thes Thesee have have foll follow owin ing g two two
-hen this magnet magnet is freely freely suspended, suspended, the
merits
two ends point in north$south direction. The
(a) They may be given desired desired regular shape. shape.
pole near the end pointing towards orth
(b) They are are strong. strong.
(north$see%ing end) is called orth pole. The (-) (-) %lec %lectr trom omag agne nett
pole near the end pointing towards ;outh
#lectrom #lectromagne agnets ts are based based on the magnetic magnetic
(south$see%ing end) is called ;outh pole.
effect of electric current. An electromagnet is
usually prepared by placing a soft iron core in a solenoid, or by winding a large number of turn turnss of an insu insula late ted d wire wire (gen (gener eral ally ly the the
nteracti nteraction on et/een et/een poles poles : The magnetic
poles e&ert forces on each other. other. 2i3e pole repel eac oter# oter# i.e., i.e., one north north pole pole will will
insulated copper wire) on a cylindrical soft
repe repell anot anothe herr nort north h pole pole or unli unli%e %e pole poless
iron core. An electromagnet electromagnet shows magnetic properties only as long as the electric current
attract each other i.e., north pole attract south
flows
pole.
through
the
solenoid.
Thus,
electromagnets electromagnets are temporary magnets.
Diffe Differe rence nce et/ et/een een
elect electrom romagn agnet et
and
permanent magnet
2ines 2ines of Magne Magnetic tic field field (Magne (Magnetic tic lines lines of
%lectromagnet :
force)
Natu ature of magn magnet etiism : Temporary. emporary. An
electromagnet shows magnetism only as long
as current flows through it.
Definition : A magnetic line of force, is a line
straight or curved, in the magnetic field of a
Polar Polarity ity : The polarity of an electromagnet
magnetic pole of magnetic dipole, such that
can be changed by reversing the direction of the current.
the tangent at any point of this line gives the
0trengt : The strength of an electromagnet
direction of the magnetic field at that point.
can be increased or decreased by increasing or decreasing the current.
Properties of Magnetic 2ines of orce These have following properties +
Permanent magnet (or -ar magnet) : Nature Nature of magnetism magnetism : Permanent (or bar)
magnets show permanent magnetism.
They are always nearly normal to the surface of magnet at every point.
Pola Polari rity ty : Polarity Polarity of a permanent permanent magnet
cannot be changed. CAREER POINT #
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They They start from from a nort nort (positive) pole and end at a sout (negative) pole.
inters rsec ectt each Two line liness of forc force do not not inte other. contractt longitud longitudinal inally ly They tend to contrac (longitudinal contraction). They tend to e6pand e6pand later laterall ally y (late (lateral ral repulsion) so as to e&ert lateral pressure on neighboring lines. (The above two properties are similar to that of a stretched rubber band). The The numb number er of magn magnet etic ic line liness of forc forcee
passing normally per unit area about a point, gives the intensity of the magnetic field at the point.
straiight ght wir wire A" is Arran rangem gement ent : A stra
%art Magnetism : #arth behaves as a huge
connected to a battery = and %ey 2. The wire
magnet (or a giant solenoid). The source of
is held hori>ontally over a magnetic needle.
this huge magnetism is given as the molten charged metallic fluid giving rise to a current flowing inside the core of the earth. This core has a radius of about 755 3m (earth
0ome Associated Terms
1. 0out 0out Magne Magneti ticc Pole Pole (0) : t is near north
geographical pole . 4. Nort Nort Magn Magneti eticc Pole Pole (N) : t is near south
geographical pole ;.
;or3ing : -hen %ey is closed, current flows
in the the wire wire in the the dire direct ctio ion n as show shown. n. The The needle deflects one side. -hen %ey is ta%en out and and curre current nt in wire wire beco become mess >ero >ero,, need needle le returns bac% to its initial position (; $ ). This shows that a magnetic field is associated with an electric current. -hen direction of current in wire is reversed, dire direct ctio ion n of defl deflec ecti tion on of need needle le is also also CAREER POINT #
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reversed. f direction of current be %ept same A9#T/ #''#/T ' /00#T 45
and wire be put under the needle, direction of
The rule states + /url the four fingers of the right hand on the palm, %eeping the thumb thumb stretched out at right angles. The thumb is straight and the fingers are circular. n case 1. thumb represents the direction of the current in the straight wire and curling of fingers represents the direction of the circular magnetic lines of force (fig.).
deflection of needle again becomes reversed.
(A) 0traigt /ire :
t means means that when the curre current nt flows flows in a straight wire, the magnetic field produced has circular lines of force surrounding the wire, having their centres at the wire as shown in fig.
The
plane
of
circular
lines
is
perpendicular perpendicular to the length of the wire. Their direction is mar%ed by arrows. curled d finger fingerss repres represent entss the n case ase 4# curle direction of the current in circular wire and thumb represents the direction of the straight magnetic lines of force. ('ig.)
ig. (a) /urren /urrentt straig straight, ht, magne magnetic tic field field circular (-) 'ircular coil :
0igh 0ightt hand hand thum thumb b rule rule for for dire direct ctio ion n of magnetic field. (') 0olenoid :
Defini Definitio tion n
:
A sol solenoi noid
is a
str straigh aightt
cylindrical core on which a large number of turns of a insulated copper wire are wrapped. t is shown in fig.
fig# () /urrent circular, magnetic field straight t means means that when the curre current nt flows flows in a circ circul ular ar wire wire (coi (coil) l),, the the magn magnet etic ic fiel field d produced has straight lines of force near the centre of the coil, as shown in figure. The parallel lines are in a plane perpendicular perpendicular to the the plan planee of the the coil coil.. Thei Theirr dire direct ctio ion n is mar%ed by the arrows. +ule : The direction of the magnetic lines of forc forcee is rela relate ted d with with the the dire direct ctio ion n of the the current by the rigt and tum rule. CAREER POINT #
;olenoid carrying a current and polarity of its face
Magnetic ield :
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orce orce on a 'urr 'urren entt 'arry 'arryin ing g ;ire ;ire due due to
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ntroduction : A current carrying conductor
produces a magnetic field around it. -hen it A9#T/ #''#/T ' /00#T 41
is plac placed ed in a magn magnet etic ic fiel field, d, the the two two
The directio direction n of the force e&perienc e&perienced ed by a
magnetic fields interact. A force acts on the
positive positive charg chargee is the same same as that on the the curr current ent
conductor.
and is given by 'leming
f is the char harge pass passeed thro hrough ugh the conductor in time t, we can write ?
%6pression : t is found by calculation that if the the cond conduc ucto torr of, of, leng length th be carry carryin ing g a curre current nt lying lying inside inside a magne magneti ticc field field of intensity " and ma%ing an angle with it, the force acting on it is given by ' ? " sin
A t
The above above relati relations onshi hips, ps, when when combi combined ned give, '?
"A t
? "v
where v is the velocity of the charged particle perpendicular perpendicular to the direction direction of the field
leming"s 2eft<=and +ule :
ntrodu ntroduction ction : -henev -henever er magne magneti ticc flu& flu&
lin%ed with a closed loop changes, an electric current is produced in the loop (a
'leming
galvanom galvanometer eter connecte connected d with closed closed loop,
the direction of motion of a current$carrying
shows a deflection). The current lasts only so
conductor when placed in a magnetic field.
long as the flu& is changing.
This rule states as follows.
This phenomen phenomenon on is called called electrom electromagne agnetic tic
;tretch out the thumb, the forefinger, and the second (middle) finger of the left hand so that
induction induction.. The electric electric current produced, produced, is call called ed induced The e.m.f. e.m.f. which which induced curre current. nt. The
these are at right angles to each other. f the
produces this current, current, is called induced e.m.f.
forefinger gives the direction of the magnetic field ( to ;), ;), the second (middle) (middle) finger the direction of current (@ to $), then the thumb gives the direction of the force acting on the
(A) Principl Principlee : t wor%s wor%s on the princi principle ple of
conductor. ;inc ;incee the conduc nducttor will will move ove in the
motion of a current carrying conductor in a magnetic field, according to 'leming
direction of the force acting on it hence the
Cand 0ule.
thumb gives the direction of motion of the
t is a device which converts electrical energy
conductor.
into mechanical energy of rotation.
orce on a moing carge
(-)Diagram :
A current$ current$carry carrying ing conducto conductorr (e.g., (e.g., a wire) e&pe e&peri rieences nces a forc orce whe when pla placed ced in a magn magnet etic ic fiel field. d. The The curr curren entt repr repres esen ents ts a colle collecti ction on of charg charged ed parti particle cless in motion motion.. Therefore, each moving charged particle in a magnetic field will also e&perience a force, called 2oren> force .
CAREER POINT #
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/urren /urrentt become becomess revers reversee in the the arms arms but couple acts in same direction as before. The coil continues rotating the shaft on which it is wrap wrappe ped. d. Thus Thus,, rota rotato tory ry moti motion on (mot (motor or action) becomes available. The rotation is not smooth with single coil. t is made smooth by increasing number of coils (multiphase motor) or preferably by having a continuous /inding.
The The elec electr tric ic curr curren entt whic which h chan change gess its its directio direction n (or polarity) polarity) after a certain certain fi&ed fi&ed interval of time is called alternating current or A/. Thus, in A/, the polarity (@ or $) is not fi&ed. fi&ed. The electricity electricity supplied supplied to our homes homes and indust industry ry in our countr country y is altern alternati ating ng current (A/). Adantages of te alternating current (A') :
igure : D' Motor
has four mains mains parts, parts, (')'onst (')'onstruct ruction ion : t ha named below. A field field magnet magnet having having concave concave magneti magneticc poles $;, which provides a strong magnetic field. An armature# which is moving part of the motor. t has two parts + (i) Bami Baminat nated ed sha shaft ft D$E D$E.. (ii) /opper /opper coil A"/ wrappe wrapped d on end D of the shaft inside the field. A pair pair of metal metallic lic split split rings rings 0 1 and 0
(commutator). A pair of metallic caron ruses "1 and ".
". -hen current passes through the coil, it flow flowss in arms arms /" and and A in a dire direct ctio ion n perpendicular perpendicular to the magnetic field. #Fual and opposite forces act on these arms (in a directio direction n accordin according g to 'leming< 'leming
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A' $enerator
(D);or3ing : A direct current (./.) source is connected between metallic brushes " 1 and
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The alte alterrnat nating curre urrent nt (A/) (A/) has has the following advantages. The alt alterna ernati tin ng curre urrent nt (A/) (A/) can be transmitted over long distances without much loss of energy and at low rate of transmission. The The alte altern rnat atin ing g curr curren entt (A/) (A/) oper operat ated ed machines such as electric fan, electric motor etc., etc., are more more durabl durablee and conven convenie ient nt as compared to those operated on direct current (/). Alternating current (A/) can be controlled by a cho%e coil at very low energy loss. n the othe otherr hand hand,, dire direct ct curr curren entt (/) (/) can can be cont contro roll lled ed only only by ohmi ohmicc resi resist stan ance cess at relatively much higher energy loss.
'onstruction of an ac generator : t consists of a rectangular coil of insulated copper wire. This This coil coil is plac placed ed in a magn magnet etic ic fiel field d between the poles of a strong permanent horseshoe magnet. This magnet is %nown as the field magnet. n actual practice, a large number of turns of the insulated copper wire are suitably suitably wound wound on an iron iron core core called called armature.
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current so produced is ta%en out through the two slip rings, and and the carbon brushes. brushes. After half the rotation (after rotating through 184G), the arms of the coil interchange their positionH the arm A" becomes the right arm and the arm / becomes the left arm. Then, the arm / starts moving downwards and the arm A" upwards. upwards. uring uring this half$rot half$rotatio ation, n, the induced current flows from / to in the arm /, and from A to " in the arm A". The two slip rings also rotate with the coil. As a result, their polarities (@ and $ poles) %eep changing at every half$rotation. half$rotation. The current which changes its polarity after regular intervals of time is called alternating curre current nt (A/). (A/). ;o, this this elect electric ric gener generato ator r produces alternating alternating current (A/). (A/).
re? re?ue uenc ncy y of te te altern alternati ating ng curr curren entt :
Alternating current (A/) so produced has a definite freFuency. This freFuency is eFual to half the number of times the polarity changes in one second. n our country, the freFuency of the the altern alternati ating ng curren currentt suppli supplied ed by the power generation units is I4 cycles per second (or C>). This means, the alternating current (A/) produced in our country changes polarity 144times 144times in one second. The two free ends of the coil are connected to the two two sli slip ring ringss 0 1 and 0 . /urr /urren entt
generated in the coil is ta%en out through the
A / genera generator tor stands stands for direc directt curre current nt
two carbon brushes " 1 and " pressed lightly
electric generator. A / generator produces direct current. A / generator is also called
against the slip rings.
D' generator
/ dynamo. A simple / generator is shown
;or3ing of an A' generator : Bet the coil
in fig.
A"/ be initially in the hori>ontal position, and is rotated in the anticloc%wise direction. -hen the coil is rotated anticloc%wise, the arm A" moves downwards and the arm / move oves
upwa upwarrds. ds.
The
coil oil
duri during ng
this his
movement cuts the magnetic lines of force, and produces induced current in the coil. According to to the 'leming< 'leming
CAREER POINT #
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The two half$split rings (0 1 and 0 ) rotate with with the the coil coil and and touc touch h the the two two carb carbon on brushed ("1, ") one by one. As a result, each carbon carbon brush brush conti continue nuess to have have the same same polarity, polarity, (@ or $). The brush " always remains positive (@) terminal, and the brush "1 remains negative ($) terminal. The current so produced is called direct current (/).
D'
generator
differ
from
an
A'
'onstruction 'onstruction of a D' generator generator : A simple
generator : The basic design of A/ and /
/ generator consists of a coil of insulated
genera generator torss is simila similarr. The The two genera generator torss
copper wire. The coil is placed between the two poles of a strong horseshoe magnet. n
differ only in the design of slip rings at the ends of the coil wire. An A/ generator use
actual practice, a large number of turns of the
two full rings called slip rings, one at each
insulated copper wire are wound on a soft
end of the coil wire, while an / generator
iron core.
has two half$rings (called split rings) of a
The two ends of the coil are connected to the
commutator.
two two halv halves es of a spli splitt ring ring (0 1, 0 called commut commutato ator). r). Two carbo carbon n brushe brushess press press against the two half$rings lightly. lightly. The current
(A) Main oard :
is ta%en out through the brushes " 1 and ".
t is provided outside the building under a
;or3ing of a D' generator : Bet the coil
cove covere red d plac placee (var (varan anda dah h or poar poarch ch). ). t
A"/ be initially in the hori>ontal position,
contains contains the meter meter (energy (energy$met $meter) er) and the
and be rotated anticloc%wise. -hen the coil is rotat rotated ed anticl anticloc oc%wi %wise, se, the arm A" moves moves
main switch. 'rom the street electric pole a thic% rubber
downwards and the arm / moves upwards.
insula insulate ted d cord cord reache reachess the the main main board. board. t
The coil during this motion cuts the magnetic
cont contai ains ns two two thic thic% % copp copper er or alum alumin iniu ium m
line liness of forc forcee and and an indu induce ced d curr curren entt is
wires, wires, one covered covered with red and the other other
produced in the coil. According to 'leming
cove covere red d
with with blac blac% %
(or (or
brow brown) n) plas plasti ticc
right hand rule, during the downward motion of the arm A", the induced induced current current flows flows from " to A in the arm A", and from to / in the arm /. The current so produced is ta%en out through the two half$split rings, and the carbon brushes. After half the rotation (rotation through 184G), the the arms arms of the the coil coil inte interc rcha hang nged ed thei their r positionsH the arm A" comes to right and the arm / to the left. Then the arm / starts movi oving upwa upward rds. s.
dow downwa nwards, rds, uri uring ng
and
this this
the
arm arm
A"
half half$r $rot otat atio ion, n,
the the
induced current flows from / to in the arm /, and from A to " in the arm A". CAREER POINT #
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covering.
As shown in fig. connection to low power devices li%e bulb " and fan ' are made with lines and B only, putting switch in line B. 'or devices of more power and with whom the body body remain remainss in conta contact ct (li%e (li%e elect electric ric press or refrigerator), we use connections through a * pin plug$soc%et (show in fig. b) system. A three pin plug P and three pin soc%et ; are They from the lie line wire (B) and neutral
shown shown in diagra diagram. m. The The three three points points of the
line line wire wire () respec respecti tivel vely y. Bive Bive line line has a
soc%et soc%et are are connec connecte ted d to the three lines as
potential of 4= whereas the neutral wire
shown in diagram. (fig. b) A fuse ' is also
has >ero potential (with respect to the earth). They enter the main board and are connected
introduced to avoid damage to the appliance.
to the meter.
The three pin plug uses a three wire cord which has three plastic wires inside a single
-iring ahead is provided by the house owner
rubber insulating cover. The wire are coloured
himself. These wires are also red and blac%
red, blac% and green to serve an e&tension of
plastic covered. 'rom the meter the wires
live, neutral and earth wires for the appliance.
enter the main switch. n the main switch, a
The three wires are connected to the three
fuse ' is provided in the live wire. A third wire is a thic% bare wire of copper,
holes holes in the the soc%et soc%et as shown shown in diagra diagram. m. -hen -hen the the plug plug is inse insert rted ed in the the soc% soc%et et,, proper lines become connected to the
call called ed eart wire #. t is connected to an earth earth connecti connection on which which consists consists of a thic% thic%
appliance.
copper plate P buried deep inside the moist
(') unction of eart /ire :
earth.
ue to long use some covered wires inside
(-)nside te uilding :
the applia appliance nce may may becom becomee bare bare and ma%e ma%e
t is a well %nown fact that inside the house, connec connecti tions ons to all all the devices devices are made in
contact with metallic body of the appliance.
parallel, each having independent switch and
n such a case the appliance gives a soc3 if not not eart earthe hed. d. The The eart earth h wire wire %eep %eepss the the
fuse fuse (if necess necessary ary). ). Thus, Thus, whenev whenever er some some
potential of the appliance >ero and shoc% is
fault occurs in circuit of one particular device
avoided.
in one room, devices in other rooms do not suffer.
%arting
Definition : /onnecting the metallic body of
a high high powere powered d electr electric ical al applia applianc ncee (e.g. (e.g. electric electric iron, refrigera refrigerator tor,, oven, oven, etc.) etc.) to the CAREER POINT #
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eart earth h wire wire of dome domest stic ic circ circui uit, t, is call called ed
and the neutral wires may become bare at
Kearthing<.
some points and come in direct contact. ue to >ero resistance, a large current is produced and a huge spar%ing is caused at the point of contact. t may cause damages and fire. This situation is called short$circuiting.
n tree pin plug# has three pins forming a
triangle. The upper pin is thic%er than the two
%lectric use
lower lower pins. pins. (fig.) (fig.) The pins pins are are connec connecte ted d
ntroduction : t is a small, simple and cheap
but very useful electric appliance used in
insi inside de the the body body of the the plug plug to the the thre threee
domestic electric circuits.
differ different ent colour coloured ed wires wires of a three three$co $cored red,,
wire wire cabl cablee L'ig L'ig.M .M.. The The colour code of the
;or3ing : -henever there is sudden voltage
rise in mains mains or Nover$loadin Nover$loadingO gO or short$
wire wiress is gree green n (#ar (#arth th$# $#), ), 0ed 0ed (Biv (Bive$ e$B) B),,
circuiting< in domestic electric circuits, the
"lac% or "rown (eutral$).
curre current nt become becomess very very large large and e&ceed e&ceedss
-enefits : ue to wear and tear with long
current current toleranc tolerancee of the electri electricc applianc appliance, e,
use, use, the the live live wire wire insi inside de the the appl applia ianc ncee
the fuse becomes hot and melts to brea% the
becomes bare (uncovered) and touches the
circui circuit. t. The applia appliance nce is saved saved from from the
body of the applicance. applicance. This contact contact raises the
damage to be caused by the large current.
potential of the body to the huge potential of the live live wire. wire. f we opera operate te that that appli applianc ancee with bare foot, we will be getting a severe shoc%.
f the appliance is earthed, its body potential
north$south.
remains >ero due to contact with the earth.
othing is felt when such an appliance is
magnetic field.
-e may may conclu conclude de that that we save save oursel ourselves ves
from severe electric shoc%s, by earthing our
er<2oading and 0ort<'ircuiting
at the point.
situations.
(ii) (ii) shor shortt$cir $circu cuit itin ing g
The number of lines of force passing through a unit area represents the strength of the field.
They are discussed ahead.
f the lines of force are closer, the magnetic
er<2oading er<2oading : -hen high powered electric
field is stronger.
applianc appliances es li%e refrigerat refrigerator or,, aircondit airconditione ioner r and
electric
iron
are
switched
on
The magnetic field lines around a current$ carrying carrying straight straight conducto conductorr are concentr concentric ic
simultan simultaneousl eously y, total total current current through through main
circle around the conductor.
wire may e&ceed the tolerance limit causing
The tangent at any point of a magnetic field line represents the direction of magnetic field
The curre current nt e&ceed e&ceedss the the limit limit under under two two
agnetic agnetic field field is represen represented ted by magnetic magnetic field lines.
electrical appliances.
(i) (i) over over$l $loa oadi ding ng
The region region around around a magne magnett in which which its magnetic force can be detected is called the
operated.
A freel freely y suspen suspende ded d magne magnett alway alwayss stays stays
The The dire direct ctio ion n of magn magnet etic ic fiel field d due due to a
damage and fire. This situation causes over$
current$ca current$carryin rrying g straight straight conducto conductorr is given given
loading.
by 'leming
0ort<'ircuitin 0ort<'ircuiting g : ue to long use wear and
tear or defective insulating material, the live CAREER POINT #
solenoid is similar to that of a bar magnet.
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The magnetic field due to a current$carrying
4@
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The magnetic field inside a solenoid is nearly
unif unifor orm m and and is para parall llel el to the the a&is a&is of the the
electr electrom omagn agneti eticc field, field, with with a conti continuo nuous us
solenoid.
chan change ge in flu& flu& due due to whic which h an emf emf is
A magnet formed due to the magnetic field of
induced.
a curr curren entt is call called ed an elec electr trom omag agne net. t. An
Power is transmitted from the power station
electrom electromagnet agnet essentially essentially consists of a soft
to cities at high voltage and low current to
iron core wrapped around with an insulated
minimi>e power loss.
copper wire coil.
9ene 9enera rato torr is base based d on the the prin princi cipl plee of
An electric motor is a device that converts
A fuse is a wire of high resistance and made up of a material of low melting point.
electrical energy into mechanical energy. t is based on the principle that + -hen a current carrying coil is placed in a magnetic field, a torFue acts on it.
-hen a conductor moves perpendicular to a magnetic field, an emf is induced across its ends. ends. The The direct direction ion of induc induced ed emf or the induc nduceed
curr urrent ent
is
det determ ermined ned
by
the
'leming
CAREER POINT #
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EXERCISE - 1
.1
-hat will be the effect on the magnitude of induced induced current current if the magnet moves faster faster
.1
-hen can an electric charge give rise to a magnetic field
.4
n what what princi principle ple does does an elect electri ricc motor motor wor%
.19
n what what prin princi cipl plee does does the the wor% wor%in ing g of a
ame the law which determines the direction of magnetic magnetic field round round a current$c current$carryi arrying ng solenoid.
.
.1
raw a diagram showing the magnetic field lines due to a current$carrying straight wire.
.7
towards the coil
generator depend .1@
an electric motor
ame the rule by which the direction of a magne magnetic tic field field inside inside a curre current$ nt$car carryi rying ng
.18
raw a diagram of an electromagnet. Cow is the polarity of the ends determined by the
.1,
;tate two characteristics of a fuse wire.
.45
oes a fuse wire have low resistance or high resistance
diagram .9
;tate two ways by which the strength of an
.41
ifferentiate between an electromagnet and a permanent magnet. magnet.
'use wire should be made up to a material of low melting point. -hy
electromagnet electromagnet can be increased. .@
-hat type of energy conversion ta%es place in a generator
solenoid is determined. .
-hat type of energy conversion ta%es place in
.44
-hy is a fuse wire fitted in a porcelain case
.47
A fuse wire is connected to a live$wire or a neutral wire
.8
-hich law determines the direction of force
.4
-hy are the switches put in the live wire
.4
-hich of the cables$rated IA and the other$
on a current$carrying conductor placed in a magnetic field
1I A$will be thic%er .,
Cow will the direction of force be changed, if the current is reversed in the conductor placed
.49
in a magnetic field
ame the place on earth where a freely suspended magnetic needle will stay (i) hori>ontal
.15
9ive the unit of intensity of magnetic field.
.11
n one one face face of a sole soleno noid id the the curr curren entt is cloc cloc%w %wis ise, e, when when loo% loo%ed ed towa toward rdss it. it. The The particular face will act as a$north pole or
.4@
;tate two factors on which the magnitude and direction of an induced emf depends.
.17
A bar magnet is moved with the north pole towards a coil. At this face of the coil the induc nduceed curren rrentt anticloc%wise anticloc%wise
CAREER POINT #
wil will
be
cloc% loc%wi wisse
.48
;tate a law which determines the direction of magne magnetic tic field field around around a curren current$ t$car carryi rying ng wire.
.4,
f a wire is bent into a circle, current flows in an anticl anticloc% oc%wis wisee direct directio ion. n. -hat -hat polari polarity ty
or
does this face of the coil e&hibit
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-hat is the shape of the magnetic field lines due to current$carrying straight conductor
south pole .14
(ii) vertical
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-hat is the direction of magnetic field at the centre of a current carrying coil if the current is in (i) anticloc%wise direction (ii) cloc%wise direction.
.71
.7
lines due to a current$carrying straight wire. .
field.
A magn magnet etic ic compa ompass ss is brou brough ghtt near near a current$carrying solenoid. -hat will be the
.
effect on the compass needle .77
Cow Cow is the the dire direct ctio ion n of magne agneti ticc fiel field d
.7
;tate any three uses of an electromagnet.
.7
;tate ;tate two advant advantage agess of an electr electroma omagne gnett
.9
escribe 'leming
.@
Cow is an electromagnet made 9ive the principle of an electromagnet. electromagnet. Cow will you
over a permanent magnet. ifferentiate between an electromagnet and a permanent magnet. magnet.
determine the polarities .8
#&plain 'leming
.,
escribe the construction and wor%ing of an electric motor with the help of a diagram.
.5
.7@
efine electromagnetic electromagnetic induction.
.78
-hat %ind of energy change ta%es place when
.7,
esc escri ribe be an e&pe e&peri rime ment nt to show show that hat a magnetic field e&erts a force on a current$ carrying conductor.
determined inside a current$carrying solenoid
.79
raw raw a diag diagra ram m to show show the the set set up of a current$ca current$carryin rrying g loop producin producing g magnetic magnetic field and show the direction of the magnetic
A freely suspended current$carrying solenoid rests along a particular direction. direction. #&plain.
.74
raw a diagram to show the magnetic field
escribe escribe with a well$lab well$labeled eled diagram, diagram, the construction and wor%ing of an A/ generator. escribe the construction and wor%ing of a
a magnet is moved towards a coil having a galvanometer galvanometer connected to its ends
.1
-hat -hat is the the use use of commu commuta tato torr in a /
.4
efine live, neutral and earth wires.
motor
.7
escribe the use of an electric fuse. Cow are
/ generator.
electric fuses of different ratings are used . .5
.1
.4
overloading Cow does an electric fuse help
-hat do you mean by a natural magnet efi efine ne a load loadst ston one. e. esc escri ribe be its its main main properties.
-hat -hat do you you mean mean by shor shortt circ circui uitt and and in both the cases
.
Eou are reFuired to ma%e an electromagnet
Ta%e a bar bar magnet magnet and a compa compass ss needl needle. e.
from a soft iron bar. raw a circuit diagram
raw a diagram for the magnetic field lines.
using a cell, an insulated copper coil and a soft iron bar.
escribe an e&periment to demonstrate that a curr curren ent$ t$ca carr rryi ying ng
cond conduc ucto torr
prod produc uces es
a
magnetic field around it.
CAREER POINT #
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EXERCISE - 2
.1
-hen a bar magnet is bro%en into two pieces7 (A) we will have a single pole on each piece (") each piece will have two unli%e poles
.4
(/) each piece piece will have two li%e poles poles
(A) up u pward
(") north
() none none of these these
(/) east
() west
.9
The magnetic field intensity produced due to a current carrying coil is ma&imum at7
bent first to form a circular circular plane coil coil of one
(A) any point
turn. The same length is now bent to give a
(") the centre of the coil
double loop of smaller radius. The magnetic field produced at the centre by the same
(/) any point lying on the a&is of the coil
current will be7
() points lying between centre of the coil
(A) a Fuarter of its first value
and its circumference circumference .7
.
A length of wire carries steady current. t is
(") a half of first value
The direction of magnetic lines of force produced by passing passing a direct current in in a conductor is7 (A) perpendicular to the conductor and coming outwards (") parallel to conductor (/) surrounding the conductor and of circular nature () perpendicular to the conductor ! coming inwards
(/) four times times its its first value value () unaltered .@
A wire as shown in figure carriers a current ampere. The semicircle has a radius r . The magnetic field at the centre / will be7
-hich of the following datermine the
(A) >ero
direction of magnetic field due to a current (")
carrying conductor (A) 'aradayQs laws of electromagnetic
(/)
induction (") 'lemingQs left7hand rule
()
(/) Ben>Qs law
14
5
r
1
r 1
r
ewtonRampere7meter ewtonRampere7meter
ewtonRampere7meter ewtonRampere7meter gauss
() a&wellQs cor% screw rule .
.8
n the figure 0 is a vertical conductor and
The intensity of a magnetic field is defined as the force e&perienced by a7
the current flows 0 to . P is point on the
(A) standard compass
hori>ontal plane and is to the south of the
(") unit positive charge
wire. The direction of the magnetic field at P
(/) unit negative charge
due to the current will be towards $
() unit north pole
CAREER POINT #
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.,
A wire carrying a current of IA is placed
(/) there are concentric lines of force around
perpendicular perpendicular to a magnetic induction of T. T.
each conductor.
The force on each centimeter of the wire is 7 (A) 1 (") 144 (/) 4.1 .15
() #ach of the conductors will move if not prevented from doing doing so.
() 14
.19
conservation of+
f a soft iron piece is buried under the surface
(A) energy
of earth in the north and south direction, then7
(") momentum
(A) it will acFuire the properties of a magnet
(/) angular momentum () charge and mass
(") its properties properties will not change change (/) it will behave li%e an insulator () canQt say with surity .11
.1@
(A) the number of turns in the coil
magnetic field " is7
.14
(") "=R
(/) Sero
() "R=
(") the resistance of the coil (/) the magnetic moment of the magnet () the speed of approach of the magnet
A proto proton n is movi moving ng with with veloc velocit ity y 146 mRs parallel to the magnetic field of intensity ;
.18
.17
(") 146
(/) 1.J 14 $1:
() Sero
(") determines the magnitude of an induced e.m.f. (/) bears no relation conservation of energy
A wire wire of lengt length h is placed in a magnetic
(/)
.1
1 "
(") ()
"
law
-hen
the
curr urrent ent
thro hrough ugh
a
sol solenoi noid
current+ (A) (A) is a cons consta tant nt and and in the the dire direct ctio ion n of
"
inducing current
The permanent permanent magnets magnets are %ept with soft
(") (") is a cons consttant ant and and is oppo opposi site te to the the direction of inducing current
(A) to magnetise the soft iron pieces
(/) increases with time and is in the direction
(") to increase the strength of the magnets
of inducing current
(/) to avoid self demagnetisation
() increases with time and is opposite to the direction of inducing current
() for physical safety of the magnets -hich of the following statement is not correct about two parallel conductors carrying
.45
A./. used in our domestic consumption has a
eFual currents in the same direction
freFuency7
(A) #ach of the conductors will e&perience a
(A) J4 C>
(/) I4 C>
(/) *4 C>
() 144 C>
force (") The two conductors will repel each other CAREER POINT #
of
incr increa ease sess at a cons consta tant nt rate rate,, the the indu induce ced d
iron pieces at ends as %eepers +
.1
the
of an induced e.m.f. .1,
1 1
to
() is useful in deciding about the direction
field ", f the current in the wire is , then ma&imum magnetic magnetic force on the wire is 7 (A) "
Ben>Qs law+ (A) is the same as the right hand palm rule
tesla. The force on the proton is 7 (A) 8 14 $1I
The induced emf produced when a magnet is inserted into a coil does not depend upon+
'orce 'orce acting acting on a stationar stationary y charg chargee in the (A)"=
Ben>Qs law is a conseFuence of the law of
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.41
A sole soleno noid id havi having ng an iron iron core core has has its its termi terminal nalss conne connecte cted d across across an ideal ideal ./. ./.
() one of the above .47
A/ is preferred because 7
source. f the iron core is removed the current
(A) it is cheap
flowing through solenoid+
(") it is easily reproducible
(A) increases
(/) it is economical in transmission
(") decreases
() it is not dangerous
(/) remains unchanged .4
() nothing can be said
A cylindrical bar magnet is %ept along the a&is of a circular coil. f the magnet is rotated
.44
/urrent is induced in a coil by
about its a&is, then.
electromagnetic induction when
(A) a current will be induced in the coil
(A) nly the coil coil moves in a magnetic field
(") no current will be induced in the coil
(") nly the magnetic is moved into a coil
(/) only emf will be induced in the coil
(/) /oil and the magnet move with respect to
() an emf and current both will be induced in the coil
each other
CAREER POINT #
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ANSWER KEY
%B%+'0% < 4
CAREER POINT #
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