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Electrostatics lab - part 3 of 4 — Transcript

by Michael Young · 5,153 words · 915 segments · language en · Watch on YouTube

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0:00stopper with the metal can
0:04but the metal piece goes through and
0:07then
0:08becomes a flat kind of thick
0:11this is the fixed leaf that's that
0:14stainless steel one
0:16and then the metal piece comes down and
0:18then
0:19soldered on it
0:23is
0:27a piece of foil now
0:30when the negative
0:34strip was brought near you saw that leaf
0:37move out and that's what they're asking
0:39here in in 17. describe the movement of
0:41electrons
0:42when the negatively strip is brought
0:44near and one of the things they want to
0:46emphasize is air is not a conductor
0:48so in other words there is air right
0:51here
0:53meaning did any of the electrons on
0:57the vinyl strip
1:00flow through the air onto the knob
1:05no it's an insulator insulator means the
1:07electrons can't flow
1:09so the electrons did not
1:12move from the strip however
1:16remember negatives are repelled each
1:18other through that electric field so
1:19even though they don't actually touch
1:22and remember this electroscope
1:25was neutral i would say
1:29that i had a bunch of positives and a
1:33bunch of
1:34negatives up here in the knob an equal
1:37number of them before
1:38i brought the strip near it when i
1:41brought it near
1:42what happened is these negatives went
1:45rushing down
1:46they were pushed away remember they can
1:48flow that was the key the electroscope
1:51is a conductor
1:52the air is not a conductor so the
1:55electrons did not
1:56flow from the vinyl onto the knob
2:00but what did happen is the electrons
2:03that were in
2:04the knob were then flowing
2:07down to not only the fixed leaf
2:11but also the movable leaf in other words
2:15remember that pit ball
2:16that was neutral and we talked about
2:18when it got close to it they separated
2:20and become polarized that's what
2:21happened
2:22here this electroscope became polarized
2:25the whole electroscope is still neutral
2:28in fact i think i'm getting
2:29to the next question in 18.
2:32but what happened is there was a
2:35response and that response was that the
2:38movable leaf moved away from the fixed
2:41leaf because both of these leaves are
2:42negative and the reason both of these
2:44leaves are negative
2:45is because they came down from the
2:49the knob that is positive
2:53and so i think i probably went farther
2:57than i needed to just for 17 but let me
2:59just backtrack to
3:00answer 17. it says here describe the
3:02movement of the electrons when the
3:04negative strip is brought near it i
3:06would say the movement of the electrons
3:07is that they moved from the knob down to
3:10the leads
3:11they really want you to get to the idea
3:13that it did not
3:15move from the strip to
3:18the vinyl ship to the electroscope okay
3:22but they moved within the electroscope
3:23because the electroscope is a conductor
3:26now i think i've also answered 18 here
3:29it says
3:30when the negatively charged strip near
3:32the electroscope
3:33what charge what is the charge of the
3:38fixed leaf
3:41and of course negative the negatives
3:44went down they went on to the fixed
3:46leaves and then it says what is the
3:48charge of the
3:49movable leaf well again
3:52the movable leaf is also negative it
3:55went they went down
3:56in fact i didn't say it but maybe i
3:58should say the obvious the reason that
4:00it moved out is because both of these
4:01are negative and we know like charges
4:03repel each other
4:06and so that's really what we saw
4:11still working on 18. what is the charge
4:15on
4:15the knob well again back to this picture
4:19the knob is positive
4:23why does the leaf move
4:27and now we just say like charges repel
4:29right the
4:30the movable leaf is negative the fixed
4:32leaf is negative they're right next to
4:34each other
4:34they're each negative and one can move
4:36so they they push apart
4:38now here's a fun one what is the charge
4:41on the whole electroscope
4:44and i would say the whole electroscope
4:46is still neutral
4:47right this is like that neutral pit ball
4:49we did in back in step
4:51uh 13. right the
4:55it is polarized if you were to add up
4:58all the positives and all the negatives
5:00in this electroscope you would get
5:02a net charge of zero but they are
5:05separated we got positives up here
5:07and i should say lack negatives up here
5:10and then we've got those lacking
5:12negatives moving down to
5:13here and so there's our our negatives
5:17so that's what is the idea of 18.
5:21well let's go on to 19. 19 says
5:24touch the negatively charged strip
5:30to the knob of the electroscope and see
5:33what happens
5:34okay so this time
5:38instead of just bringing it close and
5:41then pulling it away i'm going to
5:42actually touch it
5:43all right so remember this is negative
5:45this is vinyl so i'm going to rub it
5:47it's going to transfer electrons from
5:48the wool onto the
5:50vinyl okay and now i'm going to bring it
5:54close
5:56and not just close but touch
6:03and then pull away
6:07and hopefully what you can see on the
6:09video is now
6:11the leaf stays out it does not actually
6:14then
6:15collapse back down when i pull it away
6:20so touch
6:23the naked 19 touch the negatively
6:26charged strip to the knob of the
6:27electroscope
6:28what happens all right well i guess at
6:31this point you can just say the the leaf
6:33goes out okay but then it says
6:36remove the charge strip okay so i did
6:38that what happens
6:40and then i would say the movable leaf
6:43stays
6:44out
6:47now watch this bring the negatively
6:50charged strip
6:52near the negatively charged electroscope
6:55and see what happens
6:58all right so let me try that all right
7:00so
7:01remember i already touched it and so you
7:03can see the the movable leaf is already
7:05out
7:06does anything happen when i get closer
7:11do you see it sticks out a little bit
7:13more
7:14now when i pull it away it claps back
7:16down
7:19but there is a little bit of interaction
7:21there
7:23it it it does stick out a little bit
7:26more when i get close
7:27and then collapses back down a little
7:29bit but still remains out when i'm
7:32far from it okay and then that's what
7:35you
7:35they want you to see and so what happens
7:40then it goes on to say why do the leaves
7:43move
7:43further out well let's talk about this
7:47all right let's come back to this
7:48picture
7:49now let me change my drawing a little
7:56bit
7:58because what's different here is now
7:59i've actually touched the electroscope
8:02and so i'm going to get rid of this word
8:04air and say okay now i bring the
8:06negative
8:06all the way near and now
8:11because they touch like we did with the
8:13pitbull and i guess that was step four
8:14way back then
8:15some of the negatives can actually come
8:17off of the vinyl
8:19onto the knob
8:24so i'll put a bunch there but here's the
8:27other neat thing remember the
8:28electroscope is a conductor
8:31so when you have a bunch of negatives
8:33all packed on the knob
8:35they don't like each other they repel so
8:36they move away
8:38and so some of these and i'll just kind
8:40of erase a few of the negatives from up
8:41here
8:42we'll go down and some of them will go
8:45on to the fixed leaf
8:47and some of them will go on to the
8:49movable leaf
8:50so it's not a surprise that we saw when
8:52i touched it the leaf moved out
8:58but what is more interesting then is
9:00when i take then
9:01the negatively charged strip away
9:07those negatives are still on there
9:11and that's why the leaf remains sticking
9:13out
9:16and so that is the answer why do the
9:19well
9:19i'm sorry i haven't gotten that far yet
9:21um okay
9:23so i've only showed you that the leaf
9:25would remain out
9:27so then what would happen this is the
9:30question when i bring the negative
9:32back near it don't touch it but just
9:35bring it back near it
9:38these negatives that are in the knob are
9:41going to be chased
9:42down maybe not all of them so i'll leave
9:44one more up there
9:46but more negatives go down and that's
9:48going to make them repel even
9:50more so it goes out a little bit and
9:52when i take this strip
9:54away a few of these not all of them will
9:58go back
9:58up to here
10:01and so this negative strip as i bring it
10:05close and far
10:06is chasing electrons down and then they
10:08go back up when i pull it away but there
10:10still is an overall
10:11net negative on it because i originally
10:14touched it and so
10:15again that's what you'll you'll see here
10:16where's my my vinyl i'll show you
10:18show you again here so i bring it close
10:22and it moves out and i bring down it
10:24collapse back a little bit
10:26so it always remained out a little bit
10:27because there's the net negative on here
10:29i originally touched it
10:30but i could make more negative go down
10:32by just bringing it close to the to the
10:34knob
10:35so did you notice that the whole idea
10:38that these are conductors is really
10:39important
10:41and did you notice also that the things
10:43that are moving are these negatives i
10:44keep talking about those
10:46all right so back to this part of 19 i'm
10:49trying to answer
10:50why do the leaves move further apart
10:53then i would just say because we're
10:55chasing negatives down
10:57to the then it says check with your
11:00instructor
11:01because the atmosphere blah blah blah
11:04okay well
11:04i'm your instructor so it's working
11:06perfect all right so we don't need to
11:08check anything and i think we've kind of
11:10answered all
11:11number 20 here too it says with the
11:14negatively charged strip
11:16touching the electroscope what is the
11:18charge on the leaf
11:20so when i brought it close when i
11:22actually touched it
11:24and negative transferred onto the knob
11:26and then conducted down to the leaves
11:28those were negatives and so that first
11:30part of 20 is which ones were on the
11:32least the
11:33negative and then it says also in 20
11:36what is the charge on the whole
11:38electroscope and so in this case
11:41unlike what we did earlier when we
11:42didn't touch the electroscope this time
11:44when we touched the electrical
11:45i would say it is actually negative the
11:47whole electroscope is negative we
11:49actually transfer charge on there
11:50whereas the other one remember we just
11:51polarized the electroscope
11:52this was this one we actually touched it
11:54so the electroscope is actually negative
11:56and then of course why do the leaves
11:57remain separate separated
12:00when the strip is removed well i hope
12:01you caught that when when i pulled this
12:03away
12:03they remain separated because there
12:05still is negative there's negative on
12:06the whole electroscope
12:08the knob is negative the fixed leaf is
12:09negative the movable leaf is negative
12:11they're they're negative
12:13so like charges repel each other
12:16yeah and then the last part of 20
12:20uh why do the leaves tend to partially
12:23collapse
12:24when the strip is removed
12:27so again when the strip is close
12:32some of these negatives will be forced
12:33down to here so when it removes
12:36some negatives go up to here not all of
12:37them so this still remains up
12:39but that's why it partially collapsed it
12:41partially collapses when this
12:43strip is removed because some negatives
12:47leave the leaves and go up to the knob
12:52so a lot of interesting stuff going
12:54going on here
12:56and so hopefully you're you're catching
12:57this this whole idea because it is this
13:00fundamental concept that really
13:04sets the base for under fully
13:07understanding the electricity and
13:08magnetism stuff that's about to come
13:10throughout the
13:11the rest of the semester all right well
13:14let's keep let's keep going here number
13:1621.
13:18the electroscope is still charged
13:22negatively from the previous experiment
13:23so let me just double check yeah the
13:25leaf has still
13:25moved out charge now the acetate all
13:29right so let me come over here with the
13:30with the acetate
13:31so charge the acetate with the wool
13:35and bring it near the electroscope
13:38as you approach the electroscope what
13:40happens
13:41explain what happens as you approach the
13:43electroscope something
13:45very different could happen
13:48this is going to be hard to see so we'll
13:51hopefully see it we'll
13:52we'll see what happens here but let me
13:54just begin
13:55by getting as much charge on here i
13:57don't hear it crackling so i don't
13:59have much but we'll see what happens so
14:00if i bring it close
14:02close close close close are you seeing
14:05the leaf go down
14:08but watch this what if i get even closer
14:11closer
14:11closer closer closer oh do you see the
14:14leaf go up
14:21oh let's watch that again
14:26and fortunately the answer is pretty
14:28easy
14:31but it's kind of weird looking let's
14:32watch it again so here's the acetate now
14:34remember the acetate's positive and
14:35remember the electroscope we charge
14:36negative
14:38okay so close
14:41close close at least going down closer
14:44at least going down
14:45closer at least going down closer closer
14:48closer
14:49closer closer leaps all the way down
14:52closer still and leaf goes up
14:58why
15:02well i'll hold off on answering why
15:04because i think that's the next question
15:06here and so
15:07let's see if we can just answer 21 21
15:10the first part of it says
15:12as you approach the electroscope what
15:14happened so i would just say the the
15:15leaf begins to collapse
15:18oh then explain what
15:22is happening okay so
15:25remember these are negative let me
15:28clean up my picture a little bit so
15:31we've got negative negative negative
15:32negative negative negative negative
15:34negative negatives up here
15:36and i have this time the acetate
15:39positive getting close now
15:42remember positives attract the
15:46negatives so what would be happening
15:49is this negative here would go up to
15:52there and this negative here would go up
15:54to
15:54here and the closer i get the stronger
15:58this force is
15:59and so more and more negatives keep
16:02getting
16:03pulled up and so as they get pulled
16:06up there is less
16:09negatives
16:12on the leaves down below and that's why
16:14the leafs begin to
16:16collapse that's that's the first half of
16:18this and that's why it says explain what
16:20happens and i would just say
16:22electrons are moving up from the leaves
16:24to the knob
16:26and therefore the leaf is collapsing
16:30but where it gets really interesting
16:31here it says as you approach the
16:33electroscope
16:34very closely something different happens
16:38and you saw that the leaf begins to move
16:40out
16:42it says describe this so that's
16:44describing it the leaf begins to move
16:45out when i get real close
16:47and explain this
16:50and this is a key remember when
16:53something
16:54is neutral we don't mean no charge we
16:57mean balanced
16:58because watch if you get even closer
17:01you will pull up and hear this carefully
17:06the last of the
17:09extra electrons
17:12see at this point the leaf has
17:15completely collapsed
17:17because i have pulled up all the
17:20extra electrons are there still any
17:23electrons in here
17:25yes there are lots of electrons because
17:28remember these are just now neutral
17:30so there's an equal number of positives
17:32and negatives still in here
17:40so if you get even closer what will end
17:42up happening is you will start to draw
17:45up
17:45what i'm going to call the normal
17:49electrons
17:53and if you draw up the normal electrons
17:55you're lacking the electrons down on the
17:57leaves and the leaves are now both
17:58positive
17:59and now they begin to repel so it almost
18:02looked like something weird was going on
18:04that it was collapsing leaves and all of
18:05a sudden it started spreading out and
18:06that's true that's what happened
18:08the leaves were starting to collapse
18:09because you were pulling up the extra
18:11electrons
18:12and then when you got really really
18:13close the leaves started to spread out
18:16because you're pulling up
18:17more than the extra ones you're
18:20pulling up what i'll call the normal
18:23ones
18:24and it almost looked like something
18:26different was happening and it really
18:27wasn't it was just pulling up electrons
18:28first it was pulling up the extra ones
18:30and then it started pulling up the
18:32normal ones and so when it started
18:33pulling up the normal ones they started
18:35to become positive they started
18:36repelling to each other
18:37because remember the leaves will repel
18:38each other if they're both positive or
18:40if they're both negative
18:41so they started it with both the
18:42negative and repelling each other and
18:44became less and less and less and less
18:45negative
18:46then they started becoming more and more
18:47positive and so they begin to repel each
18:49other again
18:50so that one's a little a little trickier
18:53all right well let's move on here
18:55let's try number 22 and really kind of
18:58finally coming to the end and i hope i
19:00wasn't too
19:01uh long-winded here on this on on this
19:04first one but it's a it's a really
19:05really good
19:06lap here so we've got four more
19:08questions to do but they all kind of
19:10tie together here let me clean this
19:13up a little bit
19:16because i think the first part of 22
19:20says start with a neutral electroscope
19:24let me read it here
19:25yeah it says discharge the electroscope
19:27by touching it so remember how we talked
19:28about way back
19:29with the pith ball that if you touch it
19:31you ground it so i'm going to go ahead
19:32and
19:33take my fingers and i'm going to put my
19:35finger on it
19:37and sure enough out a little too hot
19:42but like i said i i need the heat lamp
19:44here for today
19:46but that neutralize it remember all
19:47those electrons now came on me
19:49and if just for fun i'll go ahead and
19:50neutralize myself here and so i'll
19:52ground myself
19:53say okay so there they are but i now
19:56have a
19:57neutral electroscope so discharge the
19:59electroscope so in my picture
20:01i've got a neutral electroscope and of
20:03course the leaves are collapsed i won't
20:04change it in my picture but
20:06the but the leaves are are collapsed
20:10it says charge the vinyl
20:14and uh i want to feel how warm that is
20:16because this can get
20:18a little tricky because i got to touch
20:19it okay
20:22it says charge the i'm sorry
20:25discharge the electric by touching the
20:26knob now charge the vinyl just the vinyl
20:29yeah it's got a little
20:30blue to it yeah okay so
20:33charge the vinyl strip with the wool
20:36touch the knob with one finger
20:40while maintaining contact bring
20:43the charged vinyl strip near the knob
20:48now i'll i'll divide this into a couple
20:50of steps here
20:51but if you remember way back i think it
20:54was 16 we just brought it near and
20:56pulled it away right
20:57and you you can see the the leaf move
21:00out
21:01and in our picture we were saying that
21:03because when you bring the negatives
21:04near the electrons go go down
21:07and so okay but but watch this
21:10for a moment what if i were
21:13to hold it and it's kind of warm
21:17oops i don't want to block your view
21:23what if i were to touch it
21:27maybe move it a little bit away maybe if
21:29i get the shadow side it won't be
21:30that's still pretty warm
21:41my apology i got it a little too warm
21:44for me to
21:46physically touch i wonder if i could
21:48touch it with
21:49something metal like
21:53that i can touch it with
21:58let me just see
22:02this set of staplers would work
22:10ah
22:15um not sure if this is gonna
22:19cut it maybe let's see if i can do this
22:29okay now
22:43[Music]
22:54oh that's hot okay well this was the
22:57bad side about what i just did
23:02all right maybe now i can't get push
23:05that metal real well
23:10let's see what happens here all right
23:15oh thank you all right
23:18now i'm going to mess this one up
23:23too much but
23:27if i touch it and bring it close
23:30hopefully the leaf won't go out
23:33if i don't touch it and bring it close
23:35now i got too much moisture dang it
23:41[Music]
23:45okay hang on what if i bring
23:51another one into the picture that's i
23:54haven't messed up yet
23:58let's see if i do this
24:05[Music]
24:09and it's probably got still too much
24:12moisture
24:13in it
24:20[Music]
24:27now we'll try
24:30a different one
24:32[Music]
24:39this one
24:47okay
24:53and so can i bring it close
25:04well we might have tough luck with this
25:07one because
25:08i got to get them dry for today and then
25:10i get it too hot to touch
25:19that was a little bit but i'd like for
25:22you to see it
25:24[Music]
25:26more
25:32yeah now we need to dry out so i've
25:34ruined that one for a couple of hours
25:40all right so let's see
25:44just barely moves
25:48yeah maybe but i already ruined that one
25:51by putting moisture on it all right so
25:56all right so this one is starting to dry
25:58out enough
26:00that maybe i'm at a good position where
26:03it'll be dry
26:05but not hot yet so what if i touch it
26:10bring it close pull my finger
26:13ah and pull it away good
26:17all right and you can see it losing its
26:21charge right away so it's still quite a
26:23bit of moisture inside of there that's
26:24what the
26:25the water does here but i'm not sure how
26:28well this is going to come out so
26:30let me see if i can show you a second
26:31time uh hopefully you saw it there the
26:33the first time and i guess maybe that's
26:35the
26:35good thing about a video you could see
26:37it a second time if you want
26:38but did you see it it actually moved out
26:41after
26:42i pulled the strip away see watch if i
26:45don't have my finger here and i bring it
26:46close
26:47the strip moves out and goes back
26:50nothing surprising about that that's
26:51just chasing the negatives down
26:54but my finger comes into play here
26:58when i touch it oops
27:02when i touch it instead of the electrons
27:05going
27:06down to the leaf
27:09they actually go on my finger
27:13and so if i trap them on and pull away
27:18and that barely moved out i will get
27:20positives
27:22on there and that's what they're they're
27:25trying
27:26to say uh let's read it here it says
27:29discharge the electroscope
27:31charge the vinyl strip with the wool
27:34touch the knob with one finger while
27:36maintaining contact bring the charge
27:38vinyl strip near the knob
27:40remove the finger from the knob first
27:43then remove the strip bring the charge
27:47strip of vinyl back near the knob
27:50what happens what must be
27:53the sign of the charge on
27:56the leaves all right so let me try that
28:00i'm going to neutralize it and
28:01neutralize myself
28:04i'm gonna bring it close
28:10pull my finger and then pull away and
28:13the leaf goes out
28:15and then if i bring it close notice the
28:18leaf goes down
28:20that's a sign that the leaves are
28:22positive
28:24because remember this negative strip
28:25chases the negatives down
28:30so if those leafs were already negative
28:32they would move out as they did earlier
28:34but this is a sign that by me touching
28:37it somehow i've made those leaves
28:38positive
28:40and so as i get it close it pulls them
28:43away
28:44and you can see it's losing charge
28:45pretty quickly so again this one's not
28:47as
28:47dry as it uh should be but it's actually
28:49good it's showing it it's not too hot so
28:51i can actually touch it
28:53and so that's this this whole idea
28:57and so to answer the the question number
28:5922
29:00number 22 says what happens well the
29:03leaves move
29:04down maybe i should backtrack the
29:06sentence it says
29:08bring the charge vinyl strip back near
29:10the knob what happens
29:12the leaves go down and then this
29:14question what
29:15must be the sign of the charge
29:18on the leaves well they must be
29:21then positive that's what i'm trying to
29:24convince you
29:26and then of course the physics and maybe
29:28i'll draw a picture here so you can kind
29:29of
29:29see the physics it says here in 23 while
29:32the finger was
29:33touching the knob well actually let me
29:34hold off with the questions let me draw
29:36a picture and explain
29:37so here's what's going on here i'm
29:40bringing
29:43the negative near it
29:48and as we already said earlier on that
29:50if my finger wasn't touching it it would
29:52chase negatives down and the
29:54leaves would repel but when my
29:57finger is touching it
30:07what happens is the negatives
30:10move instead of
30:13down that's why when my finger was
30:15touching and you brought it close you
30:17didn't see the leaves move out
30:19the negatives moved on to me so i'll
30:22just put
30:23me over here
30:30and so all these negatives are all over
30:32on
30:33on me and they're not down here on the
30:36leave
30:37now of course what that means is the
30:39knob
30:41is becoming positive as the negatives
30:44get chased onto
30:45me so
30:48the leaves don't do anything interesting
30:51then if i
30:52remove my finger
30:55what that does is it blocks the path
30:59for the negatives to come off of me to
31:01get back on that electroscope
31:06so when i remove my finger and
31:10remove this strip
31:13this knob which has now become positive
31:17then draws up electrons
31:21from the leaves neutralizing some of
31:24them up here
31:28and so the knob becomes less positive
31:32but in the process the leaves become
31:34positive
31:36and the leaves separate out and of
31:38course we saw
31:40that the proof that we knew the leaves
31:42were positive
31:44because when i brought the negative near
31:46it
31:47which the negatives would take some of
31:49the negatives that are up here
31:51and force them down neutralizing them we
31:54saw the leaves collapse so that was our
31:56evidence
31:57that the leaves must have been positive
31:59after we did this little weird mechanism
32:01of touching it
32:02and by the way this is called charge
32:04bipolar up
32:06induction charged by induction and so i
32:09induced a positive charge
32:11i always find it interesting that i used
32:13a negative object
32:16and i charge the electroscope positive
32:18because really what i did is i used the
32:20negative object to chase
32:21negatives off the electroscope and onto
32:24me
32:25thereby leaving the electroscope
32:27positive and so
32:28i like i said i always find this one the
32:30hardest one to understand the hardest
32:32one to explain
32:33and very interesting that i used a
32:35negative object to charge something
32:36positive
32:38so i'll say it again you use the
32:39negative to change chase them off onto
32:41something else that's why it's called an
32:42induced
32:43charge and so you're left with a
32:45positive on there
32:47so now i think we can answer the step
32:5023.
32:51it says here while the finger was
32:55touching the knob and the negatively
32:57charged vinyl was
32:59nearby what charges went on to your
33:02finger
33:03and so hopefully in that picture you
33:04said that what went on my finger were
33:05the negatives
33:06and i would say they went well beyond my
33:08finger the negatives went all throughout
33:10my
33:10my body what is the charge on the
33:13electroscope when the finger is removed
33:16see there's the key positive because
33:17remember you chase the negatives onto
33:18you
33:20therefore the electroscope is lacking
33:23the negatives when the finger
33:27and the vinyl strip are removed
33:30why were the leaves separated well the
33:32leaves separated because they are each
33:34positive and positives repel
33:38when the negatively charged strip was
33:40brought near the electroscope why did
33:42the leaves
33:43collapse well again i think i explained
33:46that
33:47that they collapsed because i was
33:48chasing negatives down
33:50to the leaves that were positive i was
33:52neutralizing them and then they had
33:54less of a repulsion and so they
33:56collapsed back down
33:58so that charge by induction is a is a
34:00tricky one but hopefully you
34:01you you see that here well that brings
34:04us really kind of to
34:06the basic end here and 24 and 25 go
34:09together
34:09uh they're kind of a little history
34:11lesson here but it says here
34:14given what you know and so what they
34:17mean by that is given that you know
34:20vinyl is negative and acetate is
34:23positive
34:24[Music]
34:25could you describe a process a procedure
34:29that we could then find the charge of
34:31other unknown objects
34:32so in this case they're going to ask us
34:34number 25
34:35to actually find out what happens with
34:39glass and what happens with rubber
34:42[Music]
34:44and there's more than one way to answer
34:46this i'll just
34:48kind of do the wrong one first
34:52the wrong one is to say
34:55start with a neutral electroscope
34:58because if you remember
35:00if you bring a negative near the neutral
35:04electroscope
35:05it chases negatives down and they repel
35:09but if you bring a positive
35:14near a neutral electroscope
35:18you suck negatives up
35:21making the leaves positives and they
35:23still repel out
35:25so you can't tell
35:29the difference in response and this
35:32electroscope between bringing a negative
35:34near it
35:35and bringing a positive near it they
35:36both make the leaves go out
35:39now i would say maybe it's a different
35:42reason because this one chases electrons
35:44down and this one sucks electrons up
35:47okay but
35:50the whole point of chapter or step 24
35:53is to point out that if you wanted to
35:55figure out a procedure to get the charge
35:58a neutral electroscope is not going to
36:01do it
36:03that's why you have to know the sign
36:06of the electroscope so let's do this
36:08let's
36:09say what if i do this what if i were to
36:11charge the electroscope by actually
36:13touching it with this and making it
36:15negative
36:16and so when i make it negative then the
36:18leaves are negative
36:20and that means if i bring a negative
36:22near it the leaves will spread out even
36:24more
36:26but if i bring a positive near it that
36:28will suck the electrons up and the least
36:29will collapse and so i'll get a
36:31different response
36:33so that's one of many ways you can
36:35answer this but no matter how you
36:37answered number 24
36:38you must start with a charged
36:40electroscope
36:42whether it's charge negative a charged
36:43positive doesn't really matter
36:45but you must have a charged electroscope
36:47you can't have a a neutral one
36:49so i will charge it
36:53negative and so that's my description
36:57i'll even show you so if i go ahead and
36:58i actually bring it close and touch it
37:01the leaf stays out

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