L14 Questions - Combustion & Flame, Science, Class 8 Video Lecture

hello friends this video on combustion
and flame part 14 is brought to you by
exam for your calm no more fear from
exam so with this we have reached
towards the end of this lesson so let us
quickly look at some of the questions
question number one list conditions
under which combustion can take place
now as I have mentioned before also that
there are three things which are
absolutely necessary for combustion to
take place first is a few other
substance you need something to burn
right otherwise there will be no
combustion so in this case the paper is
the combustible substance or the fuel
here because combustion happens in
presence of oxygen combustion is nothing
but reaction of the substance with
oxygen to release lot of heat that is
combustion and the third requirement is
heat so this heat will increase the
temperature of the substance so that it
can reach its ignition temperature
ignition temperature values for each
substance and it is that minimum
temperature at which a substance catches
fire so these are the three things which
are extremely necessary for combustion
to happen question number two fill in
the blanks burning of wood and coal
causes dash of air so when we burn food
or coal what happens they release a lot
of poisonous gases they release a lot of
smoke
so all these causes pollution of air a
liquid fuel used in homes is so one
example of a liquid fuel which is used
in home may be to light lamps yes it
could be Karason because normally you
have other fuels like petrol diesel but
we do not really use them at home fuel
must be heated to its - before it starts
burning so the minimum temperature where
it starts burning that is the ignition
temperature so any fuel has to be heated
till there ignition temperature fire
produced by oil cannot be controlled by
now how do we control fire we have
different ways we can make use of
we can make use of carbon dioxide now
water cannot be used to control fire in
some cases one such example is the
electrical equipments the other examples
is oil because oil and water they really
do not mix with each other now when they
do not mix with each other then water
will not be able to reduce the overall
temperature because water controls fire
by reducing the temperature of the
substance but in this case water doesn't
mix with oil so it will not be able to
reduce the temperature so fire caused by
oil will not be controlled by water
question number three
explain how use of CNG in automobiles
has reduced pollution in our cities CNG
is nothing but compressed nashit natural
gas so CNG is comparatively a cleaner
fuels when compared to petrol or diesel
so it is a cleaner fuel in terms of it
is very efficient because it leaves very
less residue when it is completely
burned so it completely burn the fuel if
a lot of residue is left behind so that
ICU is again going to cause trouble to
the environment right that also proves
that the fuse was not efficient enough
most of it remained there as residue so
obviously only a small part of the fuel
was actually able to produce energy but
when there is less energy residue so
that means first of all the fuel was
efficient most of the few will got
converted into energy secondly we have
less waste material present for the
environment so that is also an advantage
so that is it is very much environment
friendly and it also produced less
harmful gases when it is burned like in
case of coal anymore
cool a lot of smoke is produced lot of
harmful gases which if breathed in
causes a lot of problems in chewing
things but here comparatively the gases
which are produced they are also less
harmful so overall we can say that CNG
is
environment-friendly and that is why use
of CNG is preferred over petrol or
diesel question number four compare mpg
and good as fuels so here also if you
compare both of them you will see that
LPG is more environment friendly when
compared to hood because when both of
them are burned in mpg snow slope is
produced it is very less but input a lot
of smoke is produced which again is
hazardous for help in LPG carbon
monoxide is not produced that carbon
monoxide is a harmful gas it causes
environmental pollution it results in
acid rain so it is it is not a good gas
but in East when you born good carbon
monoxide is produced so LPG cause less
air pollution because no smoke no carbon
dioxide no harmful gases various good
causes a lot of air pollution if you
compare the calorific value you will see
that LPG has a higher calorific value
calorific value means the amount of heat
energy that is produced by burning one
kg of the fuel so that means it produces
more heat through the producing more
heat is again a characteristic of a good
fuel so that means also LPG is a better
fuel when compared to wood so you can
actually match their calorific values so
NPD's is quite higher and compared to
good question number 5 give reasons
water is not used to control fires
involving electrical equipments now when
I say water and we normally do not mean
distilled water it is not pure water so
this water contains dissolved salts and
minerals in it so this water is a good
conductor of electricity now since it
can conduct electricity so when we put
water over electrical equipments the
chances of getting electric shock
increases therefore water is not used
wherever electrical equipment is
involved instead what is used carbon
is used LPG is better domestic fuel than
good again because LPG is environment
Frankie less smoke is produced less air
pollution higher calorific value people
by itself catches fire easily whereas a
piece of paper wrapped around an
aluminium pipe does not know how easily
an object will catch fire that
completely depends on the ignition
temperature
so those substances which have very low
ignition temperature they will catch
fire very easily so the same thing
happens here ignition temperature of
paper is very less so it catches fire
very easily but the ignition temperature
of aluminium is quite higher so when you
have the same piece of paper but it is
wrapped around and Romanian so so the
overall ignition temperature increases
and that is why they do not catch fire
that easily
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