Introduction to Waves (Part -1) - Physics, Class 11 Video Lecture

hello friends this video on waves part 1
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in this lesson our introduction
transverse and longitudinal waves
displacement relation in a progressive
wave speed of a travelling wave the
principle of superposition of waves
reflection of waves beads and Doppler
effect the first question that should
strike your mind is why should we study
waves I mean why do we even have a
lesson on waves in our physics well
before I start with what is a wave what
are the different types of waves and all
the different effects related to waves I
would like to introduce the chapter with
certain applications of leaves there are
certain things which you see around
yourself every day every now and then
you use them every now and then you see
them so now we will see that even all
those things are nothing but application
of waves they are all related to waves
so I will just give you certain pictures
of the daily of the day-to-day use
examples in your own life which you see
which you come across every day so let
us look at certain such things now just
imagine you holding this this little boy
holding a thread which is tied at one
end to the wall as you see here this
thread is tied to the wall now a general
observation just imagine the situation
with yourself what happens if you just
move this light spring up and down you
see that this entire string moves in
this form and the form of a wave so that
is a wave right similarly when you see a
boat or a ship sailing over the
see or the tides what is that even that
is nothing but an example of green it is
the the boat is able to move because of
the waves I mean the boat moves up and
down the waves the ripples formed in a
lake if you drop a stone into water what
happens you see these kind of ripples
right so what are they nothing but means
again the horrible or the terrifying
earthquake which happens even that is a
consequence of earth grades that is also
because of a kind of waves under the
surface of the earth which results in
earthquake the pleasant music of a
guitar so even the strings of the guitar
when you play them what happens what is
behind that sweet or the pleasant music
which you hear nothing but waves again
your music system with beautiful songs
nothing but sound waves two persons
talking to each other you speaking with
your friend you're speaking with your
mom whatever it is whatever you speak
the other person is able to hear because
of the sound waves see you speak
something how does it reach the other
person it travels in the form of sound
waves so if you see such things are
something which you know which you
already see around your cells but maybe
they never noon that waves are an
integral part of all these things right
and even if we knew that we never
bothered to know in detail about what
waves are so that is what we will do
today so these are some of the examples
of waves and show you more and more
examples so that I can develop an
interest in you to go through this
chapter another set of examples which I
will tell you is your television remote
the remote of your TV right you sit on
your sofa and just switch on the TV
with the help of the remote you change
the channels you change the volume so
when things are so easy right so even in
that case waves play an integral part
the satellite systems through which you
get all your channels and all your
mobile phones which have become an
integral part or an unavoidable part of
our life these days the music systems at
your home the light bulb the traffic
signals the Sun this is mr. Sun Sun
gives us sunlight so even that travels
in the form of light waves the micro
beam which you generally see in your
kitchen so even there you have your
micro beams which are nothing but
electromagnetic waves I am NOT going to
detail of what kind of waves are there
in each of them right now I am just
showing the examples as I go ahead with
the chapter I will tell you about the
different types of waves how do they
propagate and what gives rise to waves
and everything else once I finish this
chapter it is your it is on your
interest that you come back to these
first three slides and try to see what
all waves are what are the kind of waves
involved in each of these examples and
that time you will find it really
interesting because by that time you
will be knowing what are the different
kinds of waves not only that even you
you would have gone to doctors when they
would have told that I want to get an
x-ray done when you get a fracture
somewhere they ask you to get an x-ray
done so even in those x-rays those
x-rays are nothing but they are also
waves similarly there are other set of
waves so I gave you an example of one
set of waves where you need a medium for
the wave to travel from one place to
another a medium is required the second
set of examples show the kind of waves
where you really don't need a medium to
propagate so the wave can propagate or
it can travel from one point to another
even without a medium and now the third
set of examples is
the waves which are related to matter
which are related to object that means
in a sense everything we see around us
is mattered right even we ourselves are
matter and there are a set of waves
which keep going or there aren't waves
inside the matter as well so when I talk
of matter you can think of just anything
which you see around yourself so in fact
you can even think of the entire
universe right so they all you can fall
under this category of examples so now
that we have seen so many applications
of waves so it is not only interesting
but it is also very very important for
us to know what a wave is so now we will
start with what is a week how do we
define wave in physics wave is a
disturbance the most important term when
you start studying wave it is a
disturbance that propagates through
space and time usually with transference
of energy so the first important term
here is disturbance the second important
term here is propagates so what this
wave it is nothing but a disturbance
what is a disturbance it is nothing but
interfering I mean how to define the
stebbins basically when something is
going that is smooth something else then
let us suppose when life is going very
smooth and in the middle of it a trouble
comes and that trouble becomes a
disturbance because it interferes with
the smoothness of your life right so
similarly V is nothing but that
disturbance which suddenly comes up and
then that disturbance propagates
propagates means I mean in in its
literal meaning properly it would mean
something which travels that will travel
or that will keep continuing with space
and time that means as time increases
with
I it it will also propagate through a
certain amount or through a certain
distance and space with transference of
energy that means energy will get
transferred from one point to another so
let us look at this example so that you
can very clearly understand wave let us
suppose this is a music which is coming
up or say this is the sound of a horn
and this is your ear so this sound
reaches your ear how does it reach your
ear because with because of these sound
waves so the sound waves travel somewhat
like this now you must be thinking in
your mind why is the sound wave looking
so dirty and yucky
we will discuss in detail about how a
sound wave travels but as of now just
keep in mind that this is I mean this is
house on what the wave will travel
basically what will happen transfer of
energy will take place from one point to
another so the initial point from where
transfer of energy starts taking place
is this this is the initial point this
is the source of the wave and this is
the final destination where the wave has
to reach so what happens the energy
transfers from this initial to this
final position with the help of the
particles in the medium but the
particles of the medium does not move
from one point to another that means
later suppose just understand this is
simply in this way let us suppose this
is your position one this is your
position - one boy is standing at
position one another boy is standing at
position two now in order to transfer
something either this boy can just walk
off with that particular thing to going
at 0.2 the other way is you transfer
this object to this point again this
point transfers the object to this point
again this point transfer the object to
this point and so on and this keeps
continuing until the object reaches
point two so in this case what happens
this point
I'm not moving right these points
actually are not moving they are all
stationary it is just that the object is
getting passed through each of these
points and gradually it is reaching from
the initial point to the final
destination
right so something like that happens
even in case of a wave if you see
observe very carefully as I denote a
point let us suppose if you observe a
particular point say this point what
happens to this point you just observe
this red dot this black particle just
move keeps moving like this if you see
like this levels like this X so it just
keeps moving in this way so basically
this particle is not going somewhere the
particle itself is not moving from
initial to final position it is just
that all particles are leaving a bit in
its own position but the energy is
getting transferred from that particle
to the next particle again from the next
particle to the next particle and so on
and thus that energy is reaching from
initial to the final position so what
what is our disturbance a disturbance is
something which causes this propagation
which initiates this movement so this
movement is initiated by a disturbance
now and then this disturbance gets
propagated that it cactus it is
transferred from one point to another
through space and time
that means time as time increases the
movement in the space also increases
with transference of energy and the next
important point is energy and not the
matter is transferred from one point to
another
please remember this very carefully if
you see here it is only the energy which
is getting transferred from one particle
to another the particles of the medium
they are not moving as such I mean they
are just move showing some movement
about their positions about their mean
position but they are not moving from
one point to another point as a whole I
mean the opposite that all the particles
are at their respective positions they
are not moving from initial position to
final position only the energy
is getting transferred from initial to
final position so that means from this
we can see that when a source of energy
causes a vibration to travel through the
medium a wave is created so here the
source of energy is nothing but this one
so when this force of energy causes of
vibration or small vibration and then it
keeps going from one to another and so
on so that vibration keeps traveling
throughout the medium then we see that a
wave is generated so not only this if we
take the next example here you can see
that it is a kind of water wave here we
can see so even here if you observe you
can see the particle see here we have
marked the particle with a red dot if
you see so that particle is not moving
with the wave the particle is just
moving in its own position it is
somewhat moving in the same way as it
was moving in the above diagram so this
red particle is just moving about its
mean position but it is not moving along
with the wave it is not getting
transferred to a complete another
location so the particles are just
moving about their mean position but the
wave as such is generated due to
transfer of energy from one point to
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