1) what is electricity ?
ANS :
Electricity
is a general term used for all phenomena caused by charge whether static or in
motion .
2) what are the types of electricity ?
ANS :
There
are two types , 1) static electricity and 2) current electricity
3) what is static electricity ?
ANS :
Static
electricity means electricity at rest in contradistinction to dynamic or
current electricity the effects of which are purely due to the electrostatic
field produced by the charge . as it is obtained by rubbing two substances such
as glass and silk it is also called frictional electricity .
4) what is current electricity ?
ANS :
Current
electricity means the electricity in motion the effects of which due to the
flow of electrons in a conductor
5) what are the types of current electricity ?
ANS :
There
are two types : 1) direct current and, 2) alternating current .
6) what are the different methods of producing electricity ?
give examples .
ANS :
The
methods are –
i)
By means of
frictions- static electricity is produced
ii)
By means of
chemical action in cells and batteries
iii) By means of mechanical driving – generator
produces electricity in two dissimilar methods .
iv) By means of heat – thermal electricity is
produced.
v)
By means of
lighting effect – electricity is produced in photo electric cell.
7) what are the sources of electricity ?
ANS :
i)
battery ii) generator , iii) thermocouple.
8) what are the applications of electricity ?
ANS :
Heating
, lighting , welding , running of motors , battery charging , electroplating ,
relays , telephones , electric equipment , etc.
9) what are the effects of electricity ?
ANS :
i)
Physiological
effect ( electric shock ),
ii)
Heating effect
( lamp , heater , fuse ) ,
iii) Magnetic effect ( fan , motor , electric bell ),
iv) Chemical effect ( battery charging and
electroplating ) and ,
v)
X- Ray effect
(X –Rays ).
10) what are A.C and D.C ?
ANS :
A.C
is the abbreviation of an alternating current which flows to and fro in a
circuit in alternating direction periodically with the variation of its
magnitude in regular manner that after reaching a maximum in one direction
decreases to zero , finally reversing and reaching a maximum in the opposite direction decreases
to zero again the cycle of pulsation being repeated continuously .
D.C
is the abbreviation of a direct current which flows in one direction only and
which does not have any appreciable pulsation in its magnitude
11) where is D.C used ?
ANS :
i)
Battery
charging
ii)
Electroplating
iii) Electrolysis,
iv) Relays,
v)
Traction
motors,
vi) Cinema projector ,
12) where is A.C used ?
ANS :
i)
House hold
appliances ,
ii)
Fan ,
iii) Refrigerators ,
iv) Power driving motors ,
v)
Radio and T.V
sets etc.
13) how will you judge whether a supply is A.C or D.C in a
premises ?
ANS :
By
seeing fan and tube connection the
nature of supply can be judged . In D.C extra resistance is used in tube light
connection and the ceiling fan’s armature only rotates whereas in A.C no
resistance is used for tube light connection and whole outer body of a fan
rotates .
14) how will you judge whether the given machine is D.C
machine or A.C machine ?
ANS :
By
seeing the enclosure the type of motor can be judged . A.C machines are always
closed type on both the sides whereas D.C machines are opened to one end for
providing brush connection from commutator fitted on projected armature shaft .
15) what are conductors ?
ANS :
Conductors
are those metallic substances which have large number of free electrons and
offer a little resistance to the flow of electricity through them
16) what are insulators ?
ANS :
Insulators
are those nonmetallic substances which have comparatively very few free
electrons and offer enormous resistance that do not practically allow
electricity to flow through them .
17) what materials are generally used as conductors ?
ANS :
Copper
. aluminium , brass , iron , phosphor bronze , silver , zinc , tungsten ,
nickel , etc.
18) what materials are generally used as insulators ?
ANS :
Mica
, oil impregnated paper , vulcanized rubber , glass , Bakelite , porcelain ,
varnished cotton , wood etc.
19) what term is used for comparing the insulation materials ?
ANS :
Dielectric
strength .
20 ) what is dielectric strength ?
ANS :
Dielectric
strength is the maximum kilovolts per millimeter which an insulating medium can
withstand without breakdown .
21) what are the factors on which the dielectric strength
depends ?
ANS :
The
dielectric strength depends on the following factors –
i)
Thickness of
the specimen,
ii)
Size and shape
of electrodes used in applying stress,
iii) Form or distribution of the field of electric
stress in the material ,
iv) Frequency of the applied voltage ,
v)
Rate and
duration of voltage application ,
vi) Fatigue with repeated voltage application ,
vii) Temperature ,
viii) Moisture content and ,
ix) Possible chemical changes under stress.
22) what is the effect of heat on insulator ?
ANS :
Insulation
resistance of moist solid dielectric with the possible exception of mica and
asbestos is decreased with the rise in temperature and increased when cooled .
23) what is the effect of moisture and impurities on insulating
materials ?
ANS :
Moisture
and impurities held in the combined form on the insulating material reduce its resistivity , increase the absorption and
dielectric loss and finally reduce the dielectric strength .
24) why is porcelain glazed for use as outdoor insulators ?
ANS :
Outdoor
porcelain insulator is glazed to prevent the surface leakage owing to
accumulation of dirts and absorption of moisture , the insulation resistance is
also increased by glazing .
25) 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 wit temperature ,
iii) Good mechanical strength ,
iv) Less specific weight,
v)
High
resistance to corrosion and ,
vi) High ductility
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