Types of Charges and their Interaction Video Lecture - Class 8

hi it's mr. Andersen and this is ap
physics essentials double-oh-seven
positive and negative charges imagine I
take a balloon that doesn't have a
charge and I rub it on my head I'm now
giving it a charge so I can move it up
to something neutral like a wall and if
I let it go it'll just stay there now
imagine if I take another balloon and I
charge that in a similar manner it
should have the same charge as the
balloon and so if I hold it up next to
it and let it go what's going to happen
it'll actually be repelled by that
object and so scientists speculated
there are two types of charges and we
call those positive and negative charges
and so an electric charge can be
positive or negative if we have a
neutral object it's going to have an
equal amount of each of those different
charges but if it's a charged object
like a balloon then it's going to have
differences in the number of electric
charges that it has if it's a negatively
charged object it's going to have more
of the negative charges and if it's a
positively charged object it's going to
have more of the positives now let's say
I bring two objects next to each other
that have different charges what's going
to happen there will be an attractive
force between the two but if we take two
objects that have the same charge and
bring them next to each other that could
be both positive or both negative
they're going to repel each other now
why did the balloon stick to the wall if
the wall didn't have a charge I hadn't
done anything to it well if you move a
charge up to a neutral object what it
can do is it can polarize that object it
can move some of the charges to one end
and what it does is create a somewhat
charged object so an electric charge can
either be positive or negative and so if
we're looking at a neutral object how
many of those charges are we going to
have in that object an equal amount of
each now let's say we take a charged
object a charged object like that
balloon what are we going to have we're
going to have more of a positive charge
if it's a positively charged object or
if it's a negatively charged object
we're going to have more of the negative
charges inside it now let's say we take
two neutral objects so two balloons that
we haven't charged and we move them
right next to each other what's going to
happen if we let them go nothing's going
to happen there's going to be no
attraction between the two because the
charges are equally distributed let's
say we take two objects that have
opposite charge so the one on the left
has a negative charge one on the right
is going to have a positive charge if I
let these go what's going to happen
there'll be an attractive force between
the two opposites attract let's say we
take two objects have the same charge
and move them next to each other in this
case they both have negative charges
what will happen when I let go they're
going to push away from each other same
thing if they're both positive if I let
them go they're going to move away from
each other now let's say we take a
charged object so that's the one on the
left and then we have a neutral object
that's going to be the one on the right
watch carefully what happens as these
two come together so as I move the
charged object towards the neutral
object what it's doing is it's
polarizing those charges it's moving the
negative charges farther away why
because they're being repelled by these
negative charges the positive charges
are moving towards it and so now there's
an attraction between this polarized
what used to be neutral object and so
Phe T makes a wonderful simulation that
kind of walks you through that so what
we've got here's the address down below
and I'll put a link in the video
description as well so what I'm going to
do is take a balloon and I can move that
balloon around and if I let it go it
just stays where it is but let's say I
want to charge it what I can do is I can
rub it on a sweater like this and now
I'm going to apply in a charge to that
balloon so when I let it go it's going
to go right over to the sweater and so
if we move it next to the wall and let
it go it'll stay there but if I get it
close to the sweater then it's going to
be attracted and so let's reset this
whole thing and look at the charges now
so you can see that all these objects
are now neutral they have equal amounts
of charge but as I rub it on the sweater
what I'm really doing is I'm pulling
those negative charges off the sweater
and now they're on the balloon so now
that balloon is a negatively charged
object and the sweater is a positively
charged object so if I let it go moves
right next to it now watch what happens
when I move it next to the wall you can
see it's polarizing this neutral object
of the wall so I'm not transferring
charges but if I move it next to it it's
attracted let's get two balloons now and
remove the wall so let me add negative
charges on this green balloon right here
and now let me add more negative charges
on this yellow balloon what's going to
happen well as I move
that balloon next to the other balloon
these are leg charges and so you can see
that they're repelling each other and it
eventually would like to go back to that
sweater okay so did you learn the
following to explain a to charge model
of electric charge again if it's a
neutral object we're going to have equal
amounts of each of those two different
charges did you learn that the
distribution of those charges tells us
if the object is going to be positively
charged or negatively you can see this
would be a negatively charged object
here and then finally did you learn to
explain how the polarization of electric
charge or separation of that charge in a
neutral object can lead to an attraction
so we have an attractive force here
between a charged balloon and what used
to be a neutral wall I hope so and I
hope that was helpful