Nuclear Fusion Energy Generation in Stars Video Lecture | Study Physics Class 12 - NEET | Best Video for NEET

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now talk about the nuclear fusion
reaction as mentioned before here
combination of two lighter nuclei will
give rise to a relatively heavier
nucleus and nucleus and here also a
large amount of energy will be released
huge amount of energy is released now in
this case temperature at I mean there is
neither important onset in a nuclear
fusion reaction what happens in a fusion
reaction two nuclei are combining to
form a heavier nucleus right now at the
same time I mentioned before also that
whenever we talk about a nucleus there
is a force of repulsion between the
protons right because all the protons
are positively charged so they tend to
repel each other and this repulsive
force is nothing but the coulombs
repulsive force right so when two
lighter nuclei come closer to each other
the coulombs repulsive force will
increase that means the two nuclei will
repel each other right so the coulombs
repulsive force becomes our opposition
to the fusion right so if we want
nuclear fusion to take place then it
should take place at a temperature at
which the protons would have enough
energy to overcome the Coulomb's barrier
now this much temperature so for this we
need a real high temperature are you
getting a point getting my point because
since in this case two nuclei will fuse
with each other only when they come
nearer now when the nucleus are coming
towards each other the repulsion between
the proton proton will increase so that
means this proton should have enough
energy to overcome the coulombs
repulsive force now
Coulomb's repulsive force is also known
as the barrier height because in this
case the coulombs repulsive force is
acting as a barrier to the phenomenon of
nuclear fusion so how do the protons how
can the protons get that much of energy
now if we rise raise the temperature to
a very high value at a very high
temperature the protons will have that
much energy that it can overcome the
Coulomb's barrier that is why nuclear
fusion always takes place at a very high
temperature so this is where the concept
of thermonuclear fusion comes into
picture what does thermonuclear thermo
means Heat nuki so heat plus nuclear
fusion that is called thermonuclear
fusion so increasing the temperature of
the material until the particles have
enough energy due to their thermal
motions alone to overcome the Coulomb
barrier this is known as thermonuclear
fusion because in keep on nuclear fusion
to take place temperature also plays an
important role so what do we do we
increase the temperature of the material
till the material gains enough energy
due to its thermal motion when it has
enough thermal energy that we can
overcome the coulombs repulsive force
then nuclear fusion can take place so
therefore this is known as thermonuclear
fusion
so for thermonuclear fusion extreme
conditions of temperature and pressure
are required application or example of
thermonuclear fusion is energy
generation in starch in stars the
temperature is extremely high and in the
in stars huge amount of energy is
generated for example take the best
example of the star that is the Sun from
Sun we get the sunlight we get such a
huge amount of energy and the cause or
the reason behind this huge amount of
jitter behind this huge generation of
energy is nuclear fusion because since
the temperature inside the Sun is very
I this fusion reaction takes place and
huge amount of energy gets released so
now we will talk about the energy
generation in Sun exactly what happens
inside the Sun energy generation in Sun
is a multi-step process that means it
occurs in different steps so there are a
total of four steps involved in the
energy generation inside Sun it is also
known as the proton proton cycle because
this process starts with protons now
what happens here let us look at that so
let us look at the first step in the
first step what happens two protons
combine together to form a do Tron which
is also known as heavy hydrogen
sometimes so this is up when two protons
combine to form this Neutron a positron
is emitted along with a neutrino and an
amount of energy is released which is
0.4 Omega electron volts now what
happens the positron which is emitted
here this positron combines with an
electron and gamma reels are formed plus
one point zero two mega electron volt of
energy is released now this Neutron
which is formed here this two train
combines with another proton and this
forms helium-3 plus gamma rays plus five
point four nine mega electron volts now
this helium nucleus which is formed here
or this hidrogen then again combine with
each other to form helium nucleus plus
this proton plus twelve point eight six
mega electron volts now the first three
steps this is step one step two step
three and step four
so the first three steps which you see
here all these steps occur twice inside
the Sun and the last step occurs only
once right so now if you combine all
these four reactions so what is the net
reaction which tells us how much total
energy is released in set by the net
fusion reactions taking place inside the
Sun for that you have to add all these
reactions all these equations so what do
you get so now if you add these four
reactions together you see that a total
of some twenty six point seven mega
electron volts of energy is released
that is four hydrogen atoms combine to
form a helium atom with a release of
twenty six point seven mega electron
volts of energy so if you want to see
how four hydrogen atoms combine to form
a helium atom with a release of twenty
six point seven mega electron volts of
energy for that you multiply this
equation by two this equation by two
this equation by two and then you add
all the four equations because these are
the processes that take place inside the
Sun now if you add them all so what do
you get so this is 2 H + 1 this is also
2 H 1 1 so you will get 4 H 1 1
Plus right now I am only considering the
left hand side okay so the left hand
side will become 2 positron plus 2
electron plus 2 H 1 2 plus 2 H 3 2 plus
2 H 1 1 so let me add it in this so this
will become 6 H 1 1 right so in this we
are not multiplying it by 2 so this is
my entire left hand side now is equal to
let us focus on the right hand side so
on the right hand side where do we have
H 1 2 that is 2 H 1 2 plus 2 positron
plus how many gamma you have 1 2 3 so
that means it will become 6 gamma plus 2
helium - 3 plus
two hydrogen plus helium nucleus plus
two neutrino right so if you see this
two positron to positron will cancel on
both sides
similarly this two hydrogen will cancel
and this will become so here two
hydrogen was there so this will become
four right because they have six
hydrogen was there so minus two hydrogen
on this side so this would become four
hydrogen
what else will cancel also here if you
see you have I am sorry this is not
hydrogen this is helium because this
helium which is formed here will again
combine with another helium to form this
so here you will have this as helium
right so this two helium here also you
have two helium so these two will cancel
out so what do I get
so the final expression which I get is
four hydrogen plus two electron again
this will also cancel out to H 1 2 to H
1 T so this will be 4 hydrogen plus 2
electron when you give helium nucleus
plus 6 gamma plus 2 nu Plus how much
energy zero point four two plus one
point zero two plus five point four nine
plus twelve point eight six so these
things will also get multiplied by two
this into two this into to this entry 2
Plus this so this comes out to be twenty
six point seven mega electron volts so
this is the final
reaction or the final nuclear fusion
reaction which takes place inside the
Sun which shows that four hydrogen atoms
combine to form an helium nucleus and
with a release of twenty six point seven
mega electron volts of energy right so
this was the reaction which has been
diagram matically mentioned when I was
talking about when I was defining
nuclear fusion so if you look at that
diagram if you go back and look at that
diagram you can see the same thing which
is represented in the form of diagrams
so this I would conclude this lesson on
nuclei so what did we study here we
studied about the structure of a nucleus
composition of a nucleus and size of the
nucleus the property of radioactivity
which is shown by certain heavy unstable
nuclei some of the terminologies related
to radioactive related to a radioactive
sample like half-life average life and
activity of a radioactive sample besides
that we talked about a very important
thing that is the nuclear energy how do
we get nuclear energy out of nucleus
what are the two processes of getting
nuclear energy that is nuclear fusion
and nuclear fusion and their
applications so now I think we are good
to go to go ahead with some of the prop
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