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around it.
The first discovery of the connection between electricity and magnetism was made
by H. C. Oersted.
The region around a magnet in which the force of attraction and repulsion exists
is called as magnetic field and it is represented by magnetic lines of force or
magnetic field lines.
Magnetic lines of force are crowded where the magnetic field is strong and far
from each other where the field is weak.
Magnitude of the field produced at a given point is directly proportional to the
magnitude of the current passing in the conductor.
Direction of the magnetic field due to current carrying conductor is specified by
Right hand thumb rule.
A coil of many turns of insulated copper wire wrapped in the shape of a cylinder is
called a solenoid.
A solenoid has all the properties of the field produced by a bar magnet.
With the help of a solenoid we can magnetise a piece of rod of a given material. If
the rod is hard steel and if the magnetic field is strong enough, a permanent
magnet can be produced.
French scientist Ampere demonstrated that a current carrying conductor placed
in a magnetic field will experience a force and the direction of this force will be
given by Fleming's left hand rule.
Electric motor works on the principle that a current carrying conductor placed in
a magnetic field experiences a force.
Michael Faraday made an important discovery that motion of a magnet with respect
to a coil or a changing magnetic field can induce an e.m.f. and produce an induced
current in the circuit. This is known as electromagnetic induction and the direction
of the induced current is given by Fleming's right hand rule.
Electric generator works on the principle of electromagnetic induction.
AC generator produces alternating current and a DC generator or dynamo produces
direct current.
In our houses we receive AC electric power of 220 V – 250 V with a frequency of
50 Hz.
One of the wires in the domestic electric circuit is live wire with red insulation
and the other is neutral wire with black insulation. The third is the earth wire
with green insulation which is connected to a copper plate and buried deep inside
the earth.
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• When electric current is passed through a conductor, it produces magnetic field
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•
• Earthing is used as a safety measure to ensure that any leakage of current to a
metallic body does not give any severe shock to a user.
• An electric fuse is a safety device used for protecting the circuits and electrical
appliances due to short circuiting or over loading.
SCIENCE & TECHNOLOGY - S.S.C.
89
MULTIPLE CHOICE QUESTIONS (MCQ's)
(Each question carries one mark)
MCQ's BASED ON CHAPTER
Moderate Level
1.
Magnetic lines of force is the path along which the unit :
a south pole moves in a magnetic field
b north pole moves in a magnetic field
R
c south pole moves away from the magnetic field
d north and south poles move in a magnetic field
s
b attract each other
c neither attract nor repel
d repel and then attract
The relation between electricity and magnetism was first established by :
a Joule
4.
5.
b Ohm
b Fleming's left hand rule
c right hand thumb rule
d none of these
What is the frequency of AC in India?
9.
12.
b solenoid
c insulator
d toroid
e
Which french scientist demonstrated the force on a current carrying conductor in a magnetic
field?
b Michael Faraday
c Hans Oersted
d George Ohm
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a Andre Marie Ampere
The director of force on a current carrying conductor in a magnetic field is given by :
a right hand thumb rule
b Fleming's left hand rule
c Fleming's right hand rule
d none of these
Which of the following is the alloy of aluminium, nickel and cobalt?
b nipermag
c alnico
d duralumin
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Electromagnetic induction was first studied by :
a Michael Faraday
11.
d 50 Hz
A coil of many circular turns of wire wrapped in the shape of a cylinder forms :
a steel
10.
c 1000 Hz
So
b 100 Hz
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d Fleming
a Fleming's right hand rule
a conductor
7.
c Oersted
The direction of the magnetic field around a straight conductor carrying current is given by :
a 150 Hz
6.
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a repel each other
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3.
Like magnetic poles :
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b C. V. Raman
c Hans Oersted
d Andre Ampere
The direction of induced current by the magnetic field in a conductor is given by :
a Fleming's right hand rule
b Fleming's left hand rule
c right hand thumb rule
d none of these
What is the PD in a domestic electric circuit between the live wire and neutral wire?
a 100 V – 120 V
b 150 V – 200 V
c 250 V – 300 V
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d 220 V – 250 V
90
Unique
MCQ's
Elementary Level
1.
2.
9.
10.
11.
12.
13.
14.
15.
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3.
Which of the following doesn't work on electromagnetism?
a electric door bell
c microphone
b generator
d electric Oven
In a bar magnet, magnetic field lines start from :
a north pole
c centre of the magnet d both the poles
b south pole
Which of the following is an incorrect statement?
a magnetic field is strong at poles
b magnetic lines of force are closed curves
c magnetic lines of force intersect each other
d the tangent to the magnetic lines of force gives the direction of the magnetic field
The magnetic lines of force due to a straight conductor are :
a closed curves
c concentric circles
b semi circles
d straight lines
The magnetic field produced due to a current through a circular loop depends directly on :
a resistance of the wire
b radius of the loop
c current passing through it
d thickness of the wire
The magnetic field produced by a given current in the conductor decreases as the distance
from the conductor :
a increases
c doubles
b decreases
d remains same
Which of the following is a device used for producing current?
a voltmeter
c galvanometer
b ammeter
d generator
At the time of short circuit, the current in the circuit :
a increases
b increases in steps
c remain same
d decreases
The direction of current in the armature coil of electric motor is reversed by :
a brushes
c magnet
b battery
d commutator
The device used for converting electric energy to mechanical energy is :
a generator
c galvanometer
b motor
d voltmeter
The presence of current in a circuit is detected using :
a galvanometer
c voltmeter
b ammeter
d generator
On which principle does the Electric generators work?
a Joule's law
b heating effect of current
c electromagnetic induction
d force on a current carrying conductor in a magnetic field
Which are the two main organs in the human body where the magnetic field produced is
significant?
a liver and pancreas
b lungs and stomach
c kidney and intestine
d heart and brain
Which of the following doesn't belong to the group?
a direct current
c brushes
b commutator
d armature coil
Which of the following is not a safety measure in using electricity?
a electric fuse
b solenoid
c insulating material
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d rubber shoes
SCIENCE & TECHNOLOGY - S.S.C.
91
Complex Level
6.
7.
8.
9.
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2.
A compass needle gets deflected when brought near a bar magnet because:
a it has pointed ends
b it is a tiny bar magnet
c it is made of iron
d it is suspended freely
Motion of the conductor is maximum when the direction of the current is:
a at 90º to the magnetic field
b same to the magnetic field
c at 180º to the magnetic field
d just opposite to the magnetic field
The direction of induced current in an AC generator changes once in each:
a two revolutions
b one revolution
c half revolution
d one fourth revolution
The alloy of iron, nickel, aluminium and titanium;
a duralumin
c alnico
b steel
d nipermag
The technique of obtaining images of human organs using magnetism is called:
a PET scan
c USG
b MRI
d CT scan
What is required for the production of current by electromagnetic induction?
a both coil and magnet must be stationary
b coil and magnet must be in relative motion
c magnetic field should be constant
d galvanometer should be deflected
The phenomenon of electromagnetic induction is the process of :
a charging a body
b generating magnetic field
c generating electric current
d exerting force on the conductor
What is the frequency of direct current (DC)?
a 50 Hz
c 0 Hz
b 150 Hz
d 100 Hz
Which of the following is not a component of DC generator?
a armature coil
c slip rings
b strong magnets
d brushes
Phase wire is also known as :
a insulated wire
c neutral wire
b live wire
d earth wire
So
1.
1.
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Mysterious Level
Which of the following work on electromagnetism?
2.
4.
c geyser
d electric iron
During a short circuit, the resistance of the circuit becomes :
a zero
b very small
c very large
d constant
The magnetic field produced at the centre of a circular loop is inversely proportional to :
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3.
b ammeter
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a thermometer
a resistance of the wire
b magnitude of the current
c radius of the loop
d time for which the current passes
The field lines inside a solenoid are in the form of :
a parallel straight lines
b closed curves
c concentric circles
d semicircles
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92
Unique
MCQ's
5.
If there is a circular coil of 'n' turns and the magnetic field produced by a single turn is 'x',
what is the total field produced?
x
n
a
c n+x
b n×x
d
x
n
6.
An electron enters a magnetic field at right angles to it as shown in the figure. What will
be the direction of force acting on the electron?
Magnetic field
a to the right
b to the left
d into the page
R
c out of the page
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MCQ's BASED ON CHAPTER
2
6
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2
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- a
7
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Mysterious Level
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3
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9
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5
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b
6
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1
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2
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b
3
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4
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5
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6
- d
7
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Complex Level
- b
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Elementary Level
1
e
Moderate Level
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Answers
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7.
Electron
In a straight wire B, current is flowing in the vertically downward direction. What will be
the direction of magnetic field lines around it?
a upward
c clockwise
b downward
d anti–clockwise
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