L6 : Nuclear force - Nuclie, Physics, Class 12 Video Lecture

hello friends this video on UTI part six
is brought to you by exam few calm no
move your prom exam please make sure
that you have watched all the videos and
part five before going ahead with part
six to start with let us consider the
lighter nuclei that means the first part
of this graph so in this portion the
mass number is less and also the binding
energy is also less so what does what
happens when the binding energy is less
I just I told you some time back that if
your binding energy per nucleon is less
that means lesser amount of energy is
required to separate the nucleons that
means the nucleons are not very tightly
bound inside the nucleons that in turn
means that the nuclei is less stable so
we can say that these such lighter
nuclei and relatively unstable so what
happens so whenever something is
unstable what happens it is a normal
tendency that everything wants to be
stable if something is unstable it tries
to become stable by some means so in
this case what happens the lighter
nuclei combine with each other and form
a heavy nuclei so two lighter nuclei
combine with each other to form a heavy
nuclei so now the binding energy for the
lighter nuclei let us represent it as
BBN and the binding energy of this heavy
nuclei heavy means it is heavier than
these lighter nuclei so this binding
energy let us represent it represent it
as EB n - right so what happens this is
unstable why it is unstable that you
know because the binding energy is less
so this nuclei that means from unstable
it combines and it forms a heavier
nuclei to become relatively stable so it
is stable compared to this right so that
means E
be and - is greater than ebn I mean
binding energy more means more stable
binding energy less means less stable so
what does this mean this means that this
energy is more than this energy so what
does that mean that means there is some
extra energy here
what is that extra energy that extra
energy is nothing but the energy which
is released in this process so that
means when two lighter nuclei combine
together to form a heavier nucleus
energy is released in this process and
this process is known as nuclear fusion
so we will talk about nuclear fusion in
towards the end of this lesson so this
is just the introduction that why two
lighter nuclei combine to form a heavy
nucleus because the lighter nuclei have
lesser binding energy so they are less
stable so they want to become stable
therefore they combine together to form
a relatively heavier nucleus which has
got better stability now in this process
a huge amount of energy is released and
this energy is made useful for various
practical purposes so this phenomenon is
known as nuclear fusion right now let us
look at the second conclusion that is
'la now let us look at for the heavier
nuclei now if the nucleus is very heavy
that means four nuclei which has got
very high mass numbers so what happens
in four such nuclei in this case mass
numbers are very high binding energy per
nucleon again is very less so in this
case this heavy nuclei how does it try
to become stable so now in this case the
heavier nuclei tries to split into two
lighter nuclei to gain little stability
so in this case this is more unstable
and this part of the system is
relatively stable I mean this part is
stable than this part right so in this
case let us suppose this binding energy
zbn and this Porsche side binding and
is EBN - so in this case what happens
this is more stable so Evie and - is
greater than ebn let's so again this
book excite energy is more so that means
this side it has this EB n plus some
extra energy that means in this process
also energy is released so that means
and this is known as nuclear fission
that means when a heavy unstable nucleus
breaks up into two lighter nuclei to
gain little stability a lot of energy is
released then this process is known as
nuclear fission right let us now look at
the third part that is we will now talk
about the constancy of the nuclear
binding energy in the mid range of the
mass number that means in this middle
portion of the graph valtor's this value
of nuclear binding energy remains
constant that is because what is this
nuclear binding energy actually
indicating it is actually indicating how
good or how bad the nucleons
are bound to each other right that is
what it is actually depicting so this is
constant right because in this portion
what happens as your mass number
increases what is happening the number
of nucleon
is increasing but actually if you see
the force which is actually present
between the nucleons that is a short
ranged force for example let us take an
example in this way let us suppose this
is one nucleon now these are the new
RIANZ
which are present inside the nucleus
right let us suppose I consider one
particular nucleon later suppose I am
considering this nucleon now this
nucleon is tightly bound to this nucleon
tightly bound to this one this one and
this one right but as the other nucleons
are going away from it the force with
which it is bound to that nucleon also
decreases that is because the nuclear
force is your short range force that
means the strength of the nuclear force
as the distance increases so that means
of any particular nucleon is affected
only by its nearest neighbors it is not
much bothered about what is happening on
the other corner for example if you
think of your colony if your next-door
neighbor switches on his television in a
very high volume right so that noise
from his television will bother you
because he is the next-door neighbor so
that noise is audible to your house but
let us suppose that the tenth house in
your colony which is almost say half a
kilometers away from your home if they
switch on their television in a loud
mode that will not bother you much so
you are most affected by your nearest
neighbors the neighbors which are
staying just beside your home similarly
in this case also a nucleon is affected
the most by its nearest neighbors so in
this mid range what happens is that as
the mass number keeps increasing the
number of nucleons keep increasing but
one particular nucleon is mut not much
bothered about the those increasing
nucleons because it is I mean it is not
getting much affected so as the mass
number increases however more nucleons
are getting added but the nearest
neighbors remain the same so the binding
energy per nucleon also remain the same
right so that is what was observed for
this range but when the number of
nucleons increases too much that means
when there are too many nucleons then
the River starts happening because when
there are too many nucleons then we see
that the binding energy per nucleon
suddenly decreases right as we saw in a
previous length that is what is
happening here at the higher end when it
increases too much
then again the binding energy starts
decreasing because the heavier nuclei
starts becoming
so when they start becoming unstable the
binding energy decreases and they start
splitting up into lighter nuclei right
so I hope you are able to understand the
concept of nuclear binding energy and
also nuclear binding energy per nucleon
so what was the significance of nuclear
binding energy it tells us how stable
and nucleuses right why did we talk
about nuclear binding energy per nucleon
because this binding energy per nucleon
gave us the initial concept of fission
and fusion that why fission and fusion
would take place at all right so it gave
us a basic framework what happens as the
mass number of elements keep increasing
so this plot of binding energy per
nucleon versus mass number moved out to
be extremely useful right so now we will
talk about nuclear force just now I
mentioned about the stuff like nuclear
force till now we have been telling that
it is because of the nuclear binding
energy that the nucleons are bound to
each other but there has to be some
force between the nucleons and that
force is known as the nuclear force so
let us quickly look at some of the
properties of the nuclear force it is a
strong attractive force that binds the
nucleons together it is the strongest
force so when you compare it with the
other forces of nature be it's the
gravitational force be it the coulombs
force be it the weak forces so this
nuclear force is the strongest of all
forces in fact this and it when you talk
when you think of your nucleus you have
got protons and neutrons right so inside
the nucleus you have protons and
neutrons now we are saying that they are
bound to each other because of this
attractive force but don't you think
that when protons are all positively
charged these positively charged protons
should repel each other
and they actually do repel each other
and the force of repulsion between these
protons is given by the Coulomb force of
repulsion so this nuclear force actually
fights with the Coulomb force of
repulsion and wins over it because
nuclear force is stronger than the
Coulomb force so the Coulomb force of
repulsion is defeated by the nuclear
force of attraction and that is why the
neutrons and protons are held together
inside the nucleus otherwise the protons
would have repelled each other and they
would have moved away from each other
right okay the third point is it is a
short range force that means that is
what we saw in the previous slide right
let us suppose if you have two nucleons
nearby then the nuclear force between
them is the strongest
now if the neutrons are moved away from
each other
the nuclear force decreases now if the
new cleon's are taken even further away
from each other that nuclear force star
decreases all the more so that means the
nuclear force is effective only for
short distances as the distance keeps
increasing the magnitude of nuclear
force keeps decreasing it is independent
of electric charge that means it does
not matter whether a nucleon is
positively charged negatively charged or
neutral that means the magnitude of
nuclear force is same between proton
proton proton Neutron or Neutron Neutron
so it is that is why it is said that it
is independent of electric charge there
is no simple mathematical form of
nuclear force like as you have seen for
gravitational force you have a
mathematical form to express or to
define gravitational force how do you
define gravitational force you say F is
equal to G m1 m2 by r square right that
is that F is not nothing but the
gravitational force similarly you have a
mathematical form of coulombs force that
is F is equal to 1 by 4 PI epsilon
naught
human q2 by r-square this determines the
force between two charged particles of
charges q1 and q2 but for nuclear force
you do not have any such mathematical
form to express it so nuclear force are
we just to know the existence of nuclear
force as we know that it is a short
range force it decreases with increasing
distance but there is no mathematical
form as such so this was all about this
was all the basic information about the
nucleus thank you please visit exam fee
or comm to watch free educational videos
try free online tests get the best
quality study materials study from the
best tutors and mentors and much more
thank you once again