L10 : Flames - Combustion & Flame, Science, Class 8 Video Lecture - Class 8 | Best Video for Class 8

hello friends this video on combustion
and came back 10 is brought to you by
example calm no more fear from exam so
we are now going to talk about flames so
everywhere we discussed about combustion
we found that the result of compassion
is either a flame or a fire so here we
are going to talk about flames and how
our claims different for different
combustible substances so what exactly
is a flame so it is a hot glowing
ignited gas during combustion now
whenever the process of combustion
happens that is the combustible
substance reacts with oxygen releasing a
lot of heat and light so how is this
heat and light released it is released
in the form of a flame now this claim
again divorced from one object to
another so if you look at a candle so
the first thing that comes to your mind
when you think of a flame is that of the
flame of a candle so if you look at the
flame how does it look it looks somewhat
yellowish to orange in color that's how
it normally looks when you see it from
far so this is the visible gas use part
it is actually gas so do you think that
plane is a solid or a liquid no it is
all gas so it is the ignited gas which
becomes visible during combustion so
that is called flame now if you look at
the flames from different objects that
has perfect candle flame or the LPG
flame or even the Bunsen burner flame so
all of them they look quite different
from each other so if you look at the
Bunsen burner thing it is more bluish in
color look you look at the candle flame
it is more yellowish or orange in color
you look at the LPG flame again there
also
your gas oven the flame there also is
little bluish in color so that type or
the structure of the flame the
color of the flame it varies from one
object to another but the question is do
all substance
produce claims during burning now we
know that combustion doesn't happen for
all substances but it happens for all
combustible substances now is it
necessary that all combustible
substances will produce claim when they
undergo the process of combustion let us
take two examples the first example is
that of a candle so in case of candle
when you light the candle when you bring
a matchstick near the panel it catches
fire and you see flames so when do you
see flames during combustion so that
means candle produce pains during
burning now let us take another example
of say charcoal so what is charcoal
charcoal is the object which is obtained
by heating wood in absence of oxygen so
if you heat good what you get is many
put charcoal charcoal also acts as a
fuel now when you burn charcoal what
happens
do you see flames now in the picture you
see it clearly shows that there is no
flame as such all you can see is a
reddish glow but there is no claim as
such so that means not all combustible
substance produced claims but in this
case heat is produced right so heat is
being produced that means this process
which is taking place in this combustion
but there are no flames so that means
not all substances produce flames during
combustion so the question is when
substances produce games substances
which vaporized during burning produce
flames now what do we mean by vaporize
that means those substances which get
converted into their papers during
burning only they produce flames now
again let's go back to the example of
the candle so in candle what do you
think is getting vaporized when it is
being burned it is the wax so the time
have you ever observed where the candle
is burning the wax is actually being
melting so that means the wax is
actually getting to those wax melts are
actually getting converted into vapors
and due to the formation of
peppers we are able to see the flame
because claim is nothing but the ignited
vapors their furs are really being
visible as flames but in case of
charcoal no vaporization is happening
nothing is nope no part of the substance
is actually getting converted into
vapors since there are no vapors
therefore there are no flames
so not only candle let us take other
examples also so if you take the example
of the gas burners so there also what
does if that is getting converted into
vapors it is nothing but the LPG the LPG
gas which is stored inside the cylinders
so LPG is stored in cylinders with most
of it being in liquid form and then
upper layer being gaseous so what what
does LPG do in order to vaporize so LPG
takes heat from the surrounding
environment and naturally reverts to a
gaseous state so in order to vaporize
what we need to do in order to vaporize
npg all that is needed is just take a
matchstick or a gas lighter in front of
it and that's all so the LBG gets
vaporized and due to the formation of
these vapors we see the flames that is
why you would have observed that if your
gas burner this area if it was weight so
if it is wet in that case even if you
bring a matchstick near it and switch it
on but it doesn't catch fire easily why
because of the presence of water so
water will lower its ignition
temperature and therefore it will not
allow it to catch fire so here also
something is getting vaporized that is
why we see flames so even if you talk
about the Bunsen burner so they are also
you see in in a Bunsen burner if you if
you have a Bunsen burner in your
chemistry lab please have a look at it
you will see that there is a pipe which
is nothing but a gas pipe this gas pipe
is connected to the bug zapper
this gas gets converted into vapors and
those vapors have seen as flames so
variable there is vaporization taking
place you will see flames and when there
is no vaporization taking place you will
not see things so it is not necessary
that their combustion is always
accompanied by formation of flames thank
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