Properties of electric charge - Electric Charges & Fields Video Lecture - Class 12

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let us talk about properties of electric
charge in properties we will basically
talk about additivity of charge I will
discuss each of them one by one
we discuss about conservation of charge
and finally we will talk about
quantization of charge so let us start
with additivity of charge so what is
additivity of charge additivity what do
you think about it knowing additivity
additivity has come from the term and it
talks about a property of addition of
charges if you have a system which has
multiple charges let us suppose if I
have a system which has charges Q 1 Q 2
Q 3 Q 4 then what does the total charge
of the system it is nothing but simple
addition of all the charges so the total
charge on the system will be Q 1 plus Q
2 plus Q 3 plus Q 4 so this property see
is that the total charge on a body is
the algebraic sum that is addition from
very good additivity it is the algebraic
sum of all the charges located anywhere
on the body right for example there is
some object I can draw it in any way I
like there is some charge Q 1 some
charge Q 2 some charge Q 3 on this body
so if somebody asks you what is the
total charge on this body then the total
charge Q will be equal to Q 1 plus Q 2
plus Q 3 doesn't matter where are these
charges located inside the body it is
the algebraic sum of all the charges now
let us suppose that we have aboard we
have an object which which is charges
for example again we have another body
which has charges Q 1 minus Q 2 plus Q 3
minus Q 4 so what is the total charge on
this body in this
case the total charge will be equal to Q
1 minus Q 2 plus Q 3 minus Q 4 it is
very important that proper signs are
taken into consideration if I have a
negative charge that negative sign has
to be taken care while summing the
charges it is not that you will just sum
P 1 plus Q 2 plus Q 3 plus Q 4 then you
will get an incorrect result so if you
are you have a negative charge that
minus sign needs to be incorporated
while calculating the algebraic sum now
let us look at the second property that
is conservation of charge you all must
have understood waters conservation of
charge because you have under you have
learned about conservation of energy
conservation of momentum so everything
is the same thing conservation of charge
also cease so conservation of charge
tells the same thing that charge can
neither be created nor destroyed
so in an isolated system the total
charge remains constant all the time so
total charge is constant what is
isolated system a system which is not
interacting with any other system so in
isolated system the total charge will
remain constant so let us take the
example which we took before the example
of the call now if you look at it before
the comb was rubbed with your hair
before that the comb was not
electrically charged right so at that
time the net charge on the system that
the system here consists of the comb
plus your hair so initially both of them
were uncharged as such right so when the
quam was rubbed with your head the comp
acquired some charges right so the total
charge before before this rubbing took
place the total charge of the comb plus
here is equal to the total charge after
the logging took place because after
rubbing the chalk the comb becomes
negatively charged so the hair becomes
positively charged so the net charge
again becomes
so before charging and after charging
the total charge remains the same so
that means the total charge before is
equal to the total charge after so
before what after what after the process
the process here is rubbing so before
rubbing also the total charge was zero
total excess charge was zero after
rubbing also the comb becomes negatively
charged at the same time your hair
becomes positively charged so after
charging also the total charge remains
the same now let us look at the third
property that is quantization of charge
he is understanding this very carefully
because this will help you as you go
ahead with this chapter what is
quantization of charge quantization
states that charge on a body can only be
an integral multiple of charge on an
electron that means any object which you
see around yourself any object let it be
anything let it be your bend let it be
your pencil let it be your house
whatever it is any object can have a
charge that charge can only be an
integral multiple of the charge on an
electron so what is the charge on an
electron the charge on an electron is
generally denoted by E and the value is
1.6 into 10 to the power minus 19
Coulomb this is the charge on one
electron and this is considered as the
fundamental unit of charge why is it
considered fundamental unit of charge
because any other charge is defined in
terms of this charge that's what this
quantization says it sees that any
object will have a charge on any object
say Q will always be it has to be an
integral multiple of electronic charge
that means that the other object cannot
have any other values other than these
values where n is
equal to 1 2 3 and so on so that means a
charge which can exist in this universe
has to be an integral multiple of this
value otherwise it can that charge
cannot exist right so this is the charge
which electron has similarly what is the
charge on a proton proton also has the
same value just that with opposite sign
because electron has negative charge the
proton has positive charge ok so I hope
it is clear to you what this
quantization quantization see is that
any charge that exists in this universe
has to be an integral multiple of charge
on an electron no other values can exist
now when I talk of quantization there
are two ways of looking at quantization
we can look at it from a macroscopic
level we can look at it from a
microscopic level let so when I talk
about macroscopic level and microscopic
level
what difference arises let us look at
that just now we saw that there are
certain values of charges which can
exist in this universe no other values
can exist other than that right so let
us suppose here and I am giving you a
practical example which happens in our
day-to-day life what do you see on the
screen you see a set of eight cars
standing in a row one after the other
right you can see that there are eight
cars very clearly standing one after the
other in a queue now let us suppose
instead of you seeing these cars so
closely let us suppose that you are
seeing it from very far off imagine that
you are sitting on an aeroplane so you
are at a very great height from the road
so if you are seeing the same thing from
such a great height
what do you see are you able to
distinguish that okay there are these
many cars or are you even able to
distinguish that these are cars no what
do you see here right now
it just appears to you as if there is a
line it just looks like a line you don't
even distinguish whether it is a card or
how many cards are there
you cannot clearly say that okay there
are eight cards if you go even more far
off it will become difficult for you to
count as well it will look exactly look
like a line so what do we learn from
this if we look at something very
closely or from a microscopic level in
that case we can see the discrete values
let us suppose with this example what I
try to explain was just now I told you
that any charge can have only these
particular values so that means
quantization talks about discrete nature
of charge that means a charge can only
take these these these discrete values
nothing else so let us suppose that each
of this card represents a discrete value
these are the values which an electron
can pay now this is true at microscopic
level because in microscopic level you
are observing microscopic levels and the
smaller level at the constituents level
so at that level you are observing
electrons very closely so you can say
that okay this value and this value it
can only take it cannot take any value
in between but when you are observing
the same thing from a macroscopic level
that is from a higher level at that time
the difference between those two charges
that is one E and two E and three E the
difference between them is very small if
you see if you look at the values if you
look at the value of E that is
electronic charge it is the various I'm
gonna do 1 point 6 into 10 to the power
minus 19 so it is a small value so the
difference between 1 e 2 e and 3 e it
doesn't appear to be huge when you look
at it from a macroscopic level right so
what do we see we see that at
macroscopic level the discrete nature of
charge is lost and it appears to be
continuous see the fact is that the
charge is discrete in nature charge can
only acts
cept values which are integral multiples
of electronic charge but when we look at
it at macroscopic level the difference
between those two acceptable values are
very small for example look at this
example this is the best example to
understand this so in this case the
discrete nature of each of the cars or
each of the values is lost it appears to
be continuous continuous means right now
those eight cars doesn't look like eight
cars it just looks like one line right
so the discrete nature of each of the
cars is lost similarly in case of
quantization the quantization concept is
lost when we look at it at a macroscopic
level so we can the quantization concept
and not be I'm sorry in at macroscopic
level the concept of quantization can be
ignored because in microscopic level
we're dealing with large values of
charges right so there are those small
values of 10 to the power minus 19 and
all day it doesn't make much difference
to it so we say that at macroscopic
level charge appears to be continuous
and quantization can be ignored whereas
when you talk about microscopic level
charge retains its discrete nature
because in microscopic level we deal
with charges which are very very small
so when we are dealing with very small
values of charges there even 10 to the
power minus 19 makes much difference
right so in this case quantization
cannot be ignored right so I hope I am
able to explain you what is quantization
and how to look at it look at
quantization from macroscopic level as
well as microscopic level so this was
all about properties of electric now we
will go ahead and study about electric
force I I already told you right that
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