1)
which materials are called elements ?
ANS :
Elements are those
materials which can neither be broken into other substances nor be created such
as gold , silver , copper , aluminium etc.
2) What
are the types of electrical materials ?
ANS :
Electrical materials
are as follows :--
i)
Conductor materials,
ii)
resistor materials,
iii)
insulating materials,
iv)
dielectric materials,
v)
semiconductor materials,
vi)
magnetic materials,
vii)
refractory materials,
viii)
structural materials,
3) what
is called resistivity or specific resistance of a material ? what is its unit ?
ANS :
The resistivity of a
specific resistance of a conductor is the resistance offered by unit meter-cube
of the material of the conductor .
4) what
is temperature coefficient of resistance ?
ANS :
Temperature
coefficient of resistance is defined as the change of resistance per degree
change of temperature per ohm of resistance .
5) what
are the classifications of electrical materials based on temperature effect ?
ANS :
electrical materials
are classified into groups e.g.
i)
positive temperature co-efficient
materials , the resistance of which increases with the rise in temperature like
copper , aluminium , gold etc.
ii)
negative temperature co-efficient
materials , the resistance of which decreases with the rise in temperature like
carbon , insulator , electrolyte etc.
6) what
are the properties of a good conductor ?
ANS :
A good conductor must
have the following properties :-
i)
low resistivity,
ii)
less variation in resistance with
temperature,
iii)
good mechanical strength,
iv)
less specific weight,
v)
high resistance to corrosion and ,
vi)
high ductility.
7) what
do you mean by superconductor ?
ANS
:
When the electrical
resistivity of many metals , alloys and chemical compounds vanishes at the
temperatures near absolute zero then they are said to be superconductor .
iridium ,lead , mercury , niobium , tin , tantalum , vanadium etc. are capable
of exhibiting superconductivity . these superconducting materials are also
known as cryogenic conductor .
8) name
some commonly used conductor materials ?
ANS :
Silver , copper ,
aluminium , mercury , brass , bronze , zinc , lead etc.
9) what
are the properties of copper ?
ANS :
i)
copper is radish brown colour,
ii)
it is malleable and ductile ,
iii)
it is specific gravity is 8.9
iv)
its melting point is 10840
c
v)
its electrical resistivity is 1.682
micro-ohm-cm.
vi)
it is one of the best conductors of
electricity,
vii)
it can be welded at red heat
viii)
it is highly resistant to corrosion,
ix)
its tensile strength varies from 3 to
4.7 tonnes/cm2
x)
it can form important alloys like
brass , bronze , gunmetal etc.
10)
what are the uses of copper ?
ANS :
Copper is used in
wired , cables , windings of generators
and transformers , overhead conductors , bus-bars etc.
11)
what is hard copper conductor and where is it used ?
ANS :
When copper conductor
is obtained by drawing cold copper bars into conductor length having
considerable mechanical strength then it is said to be hard copper conductor ,
its tensile strength is 40 kg/mm2
It is used for mainly
busbars , earthing conductor , O.H. line conductor etc. low resistivity hard
copper is used in power cables , windings , coils of insulated conductor etc.
12)
when is a conductor is identified as hard drawn ? what are its effects ?
ANS :
A conductor drawn in
cold working stage is identified as hard drawn .
Cold working distorts
the crystal structure of the metal , hardens the material , increases its
tensile strength and resistivity .
13) how
the electrical conductivity of a hard drawn conductor is restored ?
ANS :
The electrical
conductivity of a hard drawn conductor is restored by annealing under a heat treatment process
through which the regularity in crystal structure is established .
14)
what is annealed copper conductor ?
ANS :
Annealed copper
conductor is mechanically weak soft copper with tensile strength 20 kg/mm2
which can be easily shaped into any form .
15)
what is the comparison of conductivities of hard drawn copper and annealed
copper ?
ANS :
The conductivity of
annealed copper is about 4% greater than that of hard drawn copper .
16)
where is hard drawn copper conductor used and why ?
ANS :
Hard drawn copper
conductor is used in overhead line conductor due to its high tensile strength .
17)
where is annealed copper conductor used and why ?
ANS :
Annealed copper
conductors are used in wiring conductor
and winding wires of electrical machines and ttransformers due to its
flexibility and higher conductivity .
18) what are the properties of aluminium ?
ANS :
i)
pure aluminium is silvery in colour
ii)
it is ductile an malleable
iii)
its specific gravity is 2.7
iv)
its melting point is 658 0c
v)
its electrical resistivity is 2.669
micro-ohms-cm at 200c
vi)
it offers high resistance to corrosion
vii)
it is a good conductor of electricity
and heat
viii)
its electrical conductivity is next to
that of conductor
ix)
it can not be soldered or welded
easily
x)
it can form useful alloys with iron ,
copper , zinc and other materials
19)
what are the uses of aluminium ?
ANS :
Aluminium is used in
busbars , overhead line conductors like AAC
& ACSR , electrical fittings
etc.
20) why
aluminium conductors are difficult to solder ?
ANS :
When aluminium is
exposed to atmosphere an oxide layer is formed on its surface which behaves
like an insulation , therefor aluminium conductors are difficult to solder due
to the insulating property of aluminium oxide .
21) why
the contact resistance of aluminium conductors becomes very high ?
ANS :
The contact
resistance of aluminium conductors becomes very high due to the insulating
property of aluminium oxide.
22)
what are the practical uses of steel in electrical materials ?
ANS :
As the resistivity of
steel is 8-9 times higher than of copper it is not generally used as conductor
materials . galvanized steel wires are used as overhead telephone wires and
earth wires as well , due to its good mechanical properties steel is used in
ACSR conductors to increase their tensile strength .
23)
what are the composition of brass ? what are the properties of brass ?
ANS :
Brass is an alloy of
60 % copper and 40 % zinc .
Properties :
i)
brass has high tensile strength
ii)
its specific gravity is 3.3
iii)
it has high melting point of 8900c
iv)
it can be drawn into wires easily
v)
it has high resistance to corrosion
vi)
it can be soldered and welded easily
vii)
due to its higher resistivity of 7.5
micro-ohm-cm it has a lower conductivity
viii)
it is cheaper than copper
24)
what are the uses of brass in electrical field ?
ANS :
Brass is used in lamp
holders , switches, knife switches, plug points , socket outlets , sliding
contacts for starters and rheostat , etc.
25)
what are the basic composition of bronze ? how are bronzes named in different forms ?
ANS :
Bronze in its
simplest form is a binary alloy of 90 % copper and 10 % tin , it is hard and
brittle . its corrosion resistance is better than brass .
Modern bronzes are frequently
ternary alloys contacting third constituent as phosphorus , silicon , manganese
, zinc , aluminium or cadmium , the
third element is given in the name of the alloy as phosphor bronze , silicon
bronze , cadmium bronze etc.
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