[Q:-01]
What is heat ?
Ans
:
Heat is the energy possessed by a
substance in the form of kinetic energy of atomic or molecular translation,
rotation or vibration which produces a sensation of hotness.
[Q:-02]
What Is temperature and how Is it measured ?
Ans
:
Temperature is the degree of hotness or
coldness of a body. It is measured by the thermometer.
[Q:-03]
What is heating effect of electric current ?
Ans
:
Heating effect of electric current means
the transformation of electrical energy into heat energy on the passage of
electric current in a circuit of electrical conductors.
[Q:-04]
What are the different units of measuring heat energy ?
Ans
:
B.Th.U (F.P.S), Calorie (C.G.S), kilo
Calorie (M.K.S) and Joule (S.1).
[Q:-05]
Define "B.Th.U", "Calorie", "kilo Calorie" and
"Joule".
Ans
:
The British Thermal Unit (B.Th.U.) is the
unit of heat energy in F.P.S. system used by British Engineering which is
defined as the amount of heat required to raise the temperature of one pound of
water through one degree Fahrenheit.
The Calorie is the unit of heat in C.G.S
system which is defined as the amount of heat required to raise the temperature
of one gramme of water through one degree centigrade.
The kilo-Calorie is the unit of heat in
M.K.S. system which is defined as the amount of heat required to raise the
temperature of one kilo-gramme of water through one degree centigrade.
Joule is the derived S.I. unit of heat
energy which is defined as the energy dissipated in one second by a current of
one ampere flowing through a resistance of one ohm.
[Q:-06]
What is Joule's law ?
Ans
:
Joule's law states that when current flows
through a conductor heat is developed in the conductor which is proportional to
the resistance of the conductor, square of the current flowing and time in
seconds for which the current is passed, So, heat produced,
H I2RT
, ∴ H = I2RT
/ J
here J is
known as Joule's constant.
[Q:-07]
What formula is used to count heat produced?
Ans
:
Heat produced = 0.24 Vlt calories or 0.24 V2/R
t calories or 0.24 I2Rt calories.
[Q:-08]
Name some appliances which work on the heating effect of current.
Ans
:
Electric heater, Electric iron, Soldering
iron, Hot water tank, Electric kettle, Toaster, Ovens, Electric furnace, Hair
dryer etc.
[Q:-09]
An electric tea kettle has two heating coils. When one of the coils is switched
on, the kettle begins to boil in 6 minutes. When the other switched on, the
boiling begins in 8 minutes. In what time will the boiling begin if both coils
are switched on simultaneously (i) in series (ii) in parallel.
Ans
:
(i) 14
minutes, (ii) 3.43 minutes.
[Q:-10]
An electric heater is marked 750W, 220V and is found to bring 1 kg of water at
20°C to boiling point in 15 minutes. What is the heat efficiency of the heater
?
Ans
:
49-8%.
[Q:-11]
(a) What is called thermal efficiency?
(b)
What will be the thermal efficiency of a 240V, 1000W electric kettle if it
brings 2 litres of water at 15°C to boiling point in 15 minutes?
Ans
:
(a) The ratio
of useful heat to the total heat produced by electricity is called as thermal efficiency.
(b) Useful
heat = m.s.t = 2 kg x l x (100 - 15) = 170 k. calories.
Heat produced
electrically V.I.t / 4.2 x 103 k. calories
= 214.2857 k.
calories 4.2x103
Thermal
efficiency =
Useful heat / Total
heat = 170 / 214.2857
= 0.7933 i.e.
79.33%
[Q:-12]
What is fuse ?
Ans :
Fuse is a simple arrangement for the
protection of an electric circuit from excessive current and is made of a thin
strip or a wire of a material having low melting point which blows out under a
fault and isolate the faulty section from the live side.
[Q:-13]
What is the necessity of a fuse ?
Ans
:
A fuse is necessary for the protection of
an electric circuit from excessive current by blowing out the fuse and disconnecting
the supply in the circuit before creating any dangerous situation when the
current exceeds the rated value of the fuse wire.
[Q:-14]
What are the functions of a fuse ?
Ans
:
The functions of a fuse are to carry the
normal working current safely without heating and to protect an electrical
circuit from excessive current.
[Q:-15]
How is heating effect of current made in the operation of fuse ?
Ans
:
In the operation of fuse when the current
increases the rate of heat generation also increases thereby increasing the
temperature of the fuse wire. With excessive current when the temperature
further increasing reaches the melting point of the fuse wire material, fuse
melts and disconnects the power supply in the circuit.
[Q:-16]
Why does not a fuse melt at normal current ?
Ans
:
Because the temperature of the heat
developed at normal current is not sufficient to reach the melting point of the
fuse.
[Q:-17]
What are the different types of fuses according to construction ?
Ans :
The different types of fuses are as
follows :-
(i) Open type
fuse
(ii) Semi
enclosed type fuse and
(iii) Totally
enclosed type fuse.
[Q:-18]
What is called open type fuse and how is it constructed ?
Ans
:
The fuse, in which the fusing element is
exposed to the atmosphere, is called the open type fuse and it is constructed
with a porcelain plate having two terminals for connecting fusing element.
[Q:-19]
Where are the open type fuses used ? Give an example.
Ans
:
The open type fuses are generally used on
the overthead poles for giving supply to the consumer through service mains and
gang operated isolators.
Aerial fuse is an example of the open type
fuse.
[Q:-20]
Is the open type fuse safe for work ?
Ans
:
No, because one terminal always remains energized
for which there is every possibility of getting shock and catching fire due to
fall of sparking from the melted elements.
[Q:-21]
What is called semi enclosed type fuse ? Give example.
Ans
:
The fuse, where the fusing element is neither
open to atmosphere nor closed, is called the semi enclosed type fuse.
Fuse cut-out and kitkat fuse are the
examples of the semi enclosed type fuse.
[Q:-22]
How is the semi enclosed type fuse constructed ?
Ans
:
The semi enclosed type fuse is constructed
with two part porcelain base and porcelain carrier in which the base contains
two female gripping contacts connected to the incoming and outgoing terminals
and the carrier contains the fusing element placed in between two male gripping
contacts.
[Q:-23]
Where are the semi enclosed type fuses used ?
Ans
:
These are used in domestic and industrial
wiring.
[Q:-24]
Is there any possibility of fire with the semi enclosed type fuse ?
Ans
:
No, because the fusing element is covered
by its carrier in such a way that the sparking may not come outside.
[Q:-25]
What is called totally enclosed type fuse ? Give example .
Ans
:
The fuse, where the fusing element is
completely enclosed in a tube of glass or porcelain is called the totally
enclosed type fuse.
Cartridge fuse and H.R.C fuse are the
examples of the totally enclosed type fuse.
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