What is Resistivity? Video Lecture | Physics for JEE Main & Advanced

hi it's mr. Andersen and this is ap
physics essentials video 17 it's on
resistivity which is the property of
material that opposes flow of charge and
so if we were to break apart a
flashlight like this you could see that
it's not glowing that means that there's
no flow of charge in this circuit and if
we were to just test different materials
so let's take a little bit of gold and
we were to slide it into that circuit we
would see that it lights up so we know
there is flow of charge and so we would
say Gold has a really low resistivity
it's allowing that flow to move through
it if we're to try a different material
like glass in our circuit we would see
that it's not lighting up so it would
have high resistivity and if we were to
take something in the middle a
semiconductor like Silicon we would find
that some flow occurs and so we would
say this has resistivity that's going to
be somewhere in the middle and so if we
define it what is it it's essentially a
property of material that opposes
electric flow or flow of charge and so
what determines that is the structure of
the material itself it's how the atoms
and the molecules are arranged and it's
an eighth in the material each material
is going to have a different resistivity
now how could we change that well the
amount of material would be one way but
another way to change it is temperature
and so material since they're their
resistivity is based on their atomic
structure as we change temperature then
we can change the resistivity as well
and so the tendency is to confuse this
with resistance and so let's briefly
talk about what a resistor is and how it
resists flow of current in a circuit and
so if we diagram a resistor like this
what are the major parts well you're
going to have conductors on either side
you're then going to have the cross
sectional area of the resistor you're
going to have the length of the resistor
and then you're finally going to have
this resistivity which is measured in
own meters and that's going to be an
eighth in the material itself and so all
three of these lengths cross sectional
area and resistivity contribute to the
overall resistance of the resistor and
so why is that again it's the material
and how the
our range on the inside and so you can
measure this for any material but you're
also going to have to calculate cross
sectional area and the length and so we
could look at a table of different
materials and look at their resistivity
and so copper and aluminum you could
imagine are going to have really low
resistivity they don't oppose flow of
that electric charge and so if we look
at copper it's one point six eight times
ten to the negative eight it's a really
really small number but we would say
it's slightly smaller than aluminum and
so copper is going to be a better
conductor of electricity if we look at
silicon it's going to have a value
that's somewhere between that and a
insulator like glass an insulator is
going to have a really high resistivity
it's opposing almost all of that flow
and so the other thing that you should
always look for in a table like this is
the temperature and so it's going to
show us what the temperature is and
that's because the resistivity of
materials will change radically as the
temperature changes and so for material
that are metals as we increase the
temperature we're also going to increase
that resistivity in other words the best
conducting metals are going to have the
lowest temperature but if we look at a
semiconductor we find the opposite as we
increase temperature its resistivity is
actually going to go down and so you
could take certain metals
superconducting metals and they're going
to have really essentially no
resistivity and that's what we see here
a magnet hovering on top of this
superconducting metal and so did you
learn to choose the correct amount of
data you would need to measure
resistivity in the material and so you
using something not like a light bulb
but you would use a more precise
measuring device to measure the
resistance of a resistor you would then
look at the cross sectional area and the
length and then we could simply solve
for resistivity and so do you know what
it is it's an eight in all material it's
based on their structure and it opposes
flow and I hope that was helpful