L14 : Sound wave: frequency & time period - Sound, Physics, Science, Class 8 Video Lecture

hello friends this video on sound part
14 is brought to you by exam for calm no
more fear from exam so the next
characteristic that we are going to
discuss is frequency so let us now talk
about the frequency of wave
what does frequency it is the number of
oscillations per unit time so what do we
mean by that let us suppose when you
ring the bell so what happens this ball
the metal ball let me consider it like
that it keeps oscillating so how many
times it oscillated over a particular
period of time that denotes frequency
for example let us suppose if it is
moving very slow so maybe it will go
like this it will come back it'll go
like this and it will come back so the
number of oscillations now how do we
define one oscillation one oscillation
would be starting from here going to
here coming back going to here again
coming back to the main position so this
is this entire thing is one oscillation
right so now if it is moving very slow
then maybe it will cover two
oscillations in say one second if it is
moving very fast then it might cover 20
oscillations in one second so how many
oscillations it is covering in a
particular period of time that is called
frequency so let us look at this so the
same pendulum so how many times it
covered how many oscillations in a
particular time so let us look at this
picture so this is the wave so here one
oscillation starts from here it
completes at here so this is one
oscillation so till here is one
oscillation from here till here is
second oscillation from here here is
third oscillation so how many
oscillations it is covering in a
particular period of time it is denoted
by nu
and the SI unit of frequency is Hertz so
Hertz is named after the popular
scientist so frequency is measured in
Hertz now what is time period it is the
time taken to complete one oscillation
so just now I was telling you that what
is one oscillation it is it's if you
come if you start counting from here so
from here till here is one oscillation
so whatever time is taken to complete
one oscillation that is called time
period so this time would be called time
period now obviously since it measures
time therefore the SI unit is seconds
and there is a very close relationship
between time period and frequency
because if you look at it they are very
closely related so let us try to find
out the relationship between frequency
and time together so frequency is equal
to 1 by T so frequency is equal to 1 by
time period Y so let us see why it isn't
so so what is capital T it is the time
period that is standing taken to
complete one oscillation correct so that
is capital T and what is frequency
frequency is nothing but the number of
oscillations over a particular period of
time so that is frequency okay so if you
see here in capital time capital T that
is a time period t how many oscillations
are done one so how many oscillations
will be done in a particular period of
time say small T so how many
oscillations will be done this will be 1
by T so so in over a period of capital T
one oscillation is done so over a period
of one second so in in one unit of time
what will be the odd number of
oscillation that will be 1 by P
and what is frequency frequency is the
number of oscillations in unit time so
this is unit time so this one denotes
nothing but unit time that is one unit
of time so in unit time the number of
oscillations is 1 by T so and this is
nothing but frequency this is the
definition of frequency number of
oscillations in unit time so that is y
equals E is equal to 1 by T thank you
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