Introduction to Current Electricity Video Lecture - JEE

hello friends this video on current
electricity part 1 is brought to you by
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topics which we'll cover in this lesson
our electric current electric current in
conductors Ohm's law resistance and
resistivity and combination of resistors
so let us see what exactly we will gain
after going through this entire lesson
you would have observed such phenomenon
around June for example when you switch
on when you switch on the switch your
bulb glows right when it is switched off
it again dips or it could have happened
with you that you accidentally touched
the open electric socket at your home
and then you get an electric shock right
so what do you think all these are
caused so these are all nothing but what
we say in our layman terms that electric
current right so current is something
which we are going to study in this
lesson so you can take many more
examples where these things play a role
for example your battery which you use
in your in many of your electronic
devices as well as you would have seen
inverters in your home right so those
batteries are also an application of
this current flow or charge flow the
computer your desktops the electric fans
your television mobile everything which
you see around yourself all electronic
and electrical items which we see around
you I am nothing but applications of
what we are going to study now so this
lesson in the previous two lessons we
studied about charges what is an
electric charge what are the different
properties of charge so we studied about
static charges that is the chuck when
the charges the scenarios where the
charges were at rest now we will look at
the scenarios are different nominal
which take place when charges move so
what happens when charges move it gives
rise to electric current current is a
word which we normally use in our
day-to-day life right so in this lesson
we will study electric current in detail
you will see different properties of
electric current what gives rise to
electric current and many other things
so at the end of the lesson we will also
solve some problems based on the same so
let us start the lesson with what is
electric current as I just told electric
current comes into picture when I talk
about charges in motion you already know
what electric charge is right so when as
long as we imagine that my charge is at
rest it is not going anywhere so we've
talked about electrostatics
that is the charges the branch which
deals with the study of charges at rest
the moment I talk about charges moving
when the charges start moving we no more
talk about statics we talk about
dynamics now the flow of charges
constitute electric current so electric
current is nothing but when charges flow
electric current is setup very simple
right so how do we basically measure
electric current how do I know how much
electric current is flowing through a
particular wire I mean I know that all
of you are aware of what a current is or
in what context we use current we often
say right say for example let us suppose
your mobile for charge if you have
plugged in to the switchboard you say
that now when your mobile is getting
charged you see that current is flowing
through this wire right so that means
there has to be something there has to
be some parameter which will measure
current I mean how will I measure
current so current is basically measured
as the rate of flow of charge so what do
I mean by
the flow of charge that means how much
charge is flowing with respect to time
so let us suppose if I say how much
amount of charge if I say let us say 10
coulombs of charge had flown in 1 second
so we say what is my current my current
is nothing but 10 Coulomb per second so
that is my current so electric current
is basically measured as the flow of
charge per unit time right so we can
write this as let us suppose if I denote
electric current with I so electric
current is nothing but time
rate of change of electric charge so we
can write it as DQ by DT right it is
generally denoted by capital I the SI
unit of current is amperes which is
denoted by capital a like the way we
have SI unit for charge as Coulomb
similarly we have the SI unit of
electric current as ampere so how do we
define ampere and from where does this
word ampere King come we will study
about that in the next slide so let us
take the simple example this is a simple
circuit which is drawn here normally
just - since we are just at the first
slide of the chapter let let me tell you
few very small things whenever you see
an electric circuit which is drawn for
you this represents nothing but the
source of voltage this is basically the
source of the current from this will
give rise to current so this is nothing
but your battery this battery is
represented in your electric circuit
with two lines I lack a smaller line and
along the line so the longer line
generally denotes the positive terminal
and the shorter line generally denotes
the negative terminal so this is your
battery which is the source of your
current right what is this this
kind of symbol generally denotes the key
key on which you can say as a switch if
the key is in this position that means
the switch is right now off that means
there is no current flowing through the
circuit for example this bulb is
attached in this circuit when will the
bulb glow when you switch it on when you
switch on the circuit then the current
will flow right right now the switch is
open so there is no current flow in the
set now as soon as the key is pressed as
you just saw the key is pressed so your
subject becomes a closed circuit so the
current flows through the circuit and
the bulb closed right this is what
basically I mean this what happens in a
basic circuit you switch on the key I
just told you how we represent a key how
we represent a battery source so that
you don't have issues when you go ahead
but because as we go ahead we will draw
a more complicated circuits all right
so till now what did I study I basically
studied that electric current is nothing
but moving charges constituted whenever
charges move electric current is
produced it is denoted by a capital I
the SI unit is impaired we measured it
as time rate of change of charge flowing
right that is rate of flow of charge now
what about the direction of current now
let me clarify a very important thing
right away
however I am talking about the direction
of current but that doesn't mean that
current has a specific direction this
direction of current basically talks
about from where will the current origin
originate and where will it terminate
right so normally what happens is if you
look at this circuit what will happen
normally this is the negative electrode
right of the cell so this negative
electrode will give rise to
many electrodes so your electrons when I
talk about electric charge electric
charge is nothing but your electrons so
the electrons will flow in this
direction this is how the electron will
flow so this is the direction of
electronic current so electronic current
is basically the current which is in the
direction of flow of electrons now if
the electrons are moving in this
direction where will the positive
charges move the positive charges will
move in this direction right so that
current is known as conventional current
so the current constituted by the
electrons is known as electronic current
and the current constituted by the
positive charges that is opposite to the
electronic current is the conventional
current now when I say current what do I
mean is it electronic current or
conventional current because at one time
you can assume it to be either
electronic or conventional current right
let us suppose if I say that okay what
we will do we will always consider that
current will start from negative and it
will end in positive or we will assume
that current will always start from
positive and it will end in negative but
in no case you can ask you both things
right so basically what convention we
followed is the direction of current is
opposite to the direction of flow of
electrons that means the direction of
current is opposite to electronic
current that is why this other current
is known as conventional current because
according to convention this direction
of current is considered as the
direction of current so in any circuit
current is always assumed to flow from
positive towards negative right so
conventional current or in general
electric current always the direction of
electric current is always opposite to
the flow of
electrons now please don't ask why is it
so because there is no precise answer to
this this was what was devised by the
physicists at that time they decided
that okay let us follow this convention
and since that time this convention has
has been followed so it is nothing but a
matter of convention that we consider
that the direction of current is
opposite to the direction of flow of
electrons here so you are clear with the
electronic current and conventional
current part ok thank you please visit
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