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- [Voiceover] Let's now tackle
the rest of this problem.

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So they say a light-bulb is non-ohmic

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if its resistance changes
as a function of current.

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Your setup from part a, which
we have right over here,

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is to be used or modified
to determine whether

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the light-bulb is non-ohmic.

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How, if at all, does the
setup need to be modified?

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Well, we want to be able
to change the current

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that's going through the light-bulb

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and then see how the resistance changes,

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so what we could do, we
could always measure it

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with the setup right over here.

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It's very easy to measure the resistance.

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So we can measure resistance by,

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we know that V is equal to,

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we know that voltage is equal
to current times resistance

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or that resistance is equal
to voltage divided by current.

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So, if we know the current

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going through a light-bulb

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and we know the voltage across it,

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we can always figure out the
resistance of the light-bulb.

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So our set-up right here
is actually very good

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for figuring out the resistance

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of the actual light-bulb.

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And so we need to change the current

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and see how the resistance changes.

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And there's a couple of ways

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that we could change the current.

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We could change some
other resistance here,

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but lucky for us we have
a variable power source,

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so we can change the voltage,

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we can change the voltage
across the entire circuit,

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and by changing the voltage

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across the entire circuit,

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well that's going to change
the current that is going.

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This is a simple circuit.

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It's just going in series.

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The current is just doing like that,

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and so if we change the current
through the entire circuit,

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we would be changing the
current through the light-bulb,

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and then we could just measure V and I

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and figure out whether R changes as well.

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So, how, if all, does the
setup need to be modified?

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I could say it doesn't
need to be modified.

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Doesn't need modification.

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Modification.

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All right.

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And then the next section,

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what additional data, if any,

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would need to be collected.

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Well, I would want to,

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I would want to measure.

53
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Let me even do this part down.

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Let me do it, part c, over here.

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So, part c.

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So, part one of part
c was no modification.

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No modification.

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No mod, I can explain that.

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I can change resistance.

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I can change,

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I can change current

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by varying power source.

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By varying power source.

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Power source.

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I can measure,

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I can measure resistance

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of bulb

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by voltage across bulb,

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across bulb,

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divided by,

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divided by current

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entering or exiting bulb.

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And I know the first part of this test

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we were saying, hey,

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do we have the same number
of electrons per second

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entering the bulb or exiting the bulb,

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but from what we know of currents,

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we know that the current
is going to be the same

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on either side.

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You have a voltage drop,
but the current is the same.

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And so entering or exiting,

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you're going to get the same value,

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and even if you didn't
know what I just told you,

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the first part of the experiment
would have told you that,

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that your current is the same

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entering and exiting the bulb.

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And so, this right over here

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is going to be equal to
the resistance of the bulb.

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So I can change the current
by varying the power source,

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and then I can see what value I get for R

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by measuring these things

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as I change that overall current for my,

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for my setup.

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Let's see b.

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What additional data, if any,
would need to be collected?

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So, part two.

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Part two here.

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I'd need to collect,

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collect voltage

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across,

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across bulb

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as current changes,

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or it'd be as I change
my variable power source.

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As I vary power source,

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power source,

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and I would also have to collect,

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maybe I'll write it this way,

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I'll collect that, voltage.

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I'll write it like that.

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Voltage across bulb as
I vary power source,

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and I could say current,

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current entering,

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exiting bulb

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as I vary power source.

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Power source.

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So I'd have to measure these things

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and then I'll be able to
figure out if my R changes.

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All right, let's tackle part d now.

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How would you analyze the data

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to determine whether the bulb I non-ohmic?

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Include a discussion of
how the uncertainties

122
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in the voltmeters and ammeters
would affect your argument

123
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for concluding whether the
resistance is non-ohmic.

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Well, I explained it a
little bit, well, up here,

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but I'll write it again.

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d, so, let me read that one more time.

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How would you analyze the data?

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So, what I would do is,

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so, power source,

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I would make one voltage for,

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I would vary power source,

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source to first voltage,

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voltage,

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and measure,

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measure what is described above,

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and measure above.

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Use to calculate,

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use to calculate the resistance,

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resistance of bulb.

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And then, vary

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power source

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to second voltage,

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voltage, and once again,

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measure above,

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measure above.

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See if resistance changes,

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see if resistance

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changes.

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So, we could say,

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if V across bulb,

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across bulb,

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over, let me actually, let
me just write it this way.

153
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All the Vs are cross above with.

154
00:07:09,578 --> 00:07:11,749
V_one over the current_one,

155
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so this is the voltage across the bulb

156
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over the current across the bulb.

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If this is equal to, after I change it,

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the voltage across the bulb

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divided by the current across the bulb.

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If this over here,

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if these are equal,
then I am dealing with,

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the resistance has not changed,

163
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and so we could say,

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well non-ohmic,

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non-ohmic is when the
resistance does change.

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If resistance, so we could say,

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non-non-ohmic, or I could say

168
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not non-ohmic,

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non-ohmic,

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otherwise if V_one over
I_one does not equal,

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let me write that, I wrote V_i.

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Let me write V_one,

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V_one over I_one does not equal

174
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V_two over I_two, then we are non-ohmic.

175
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And we have to be careful,

176
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because the sensitivities of
our voltmeters and ammeters

177
00:08:17,302 --> 00:08:19,090
might give us an aberrant result.

178
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For example, we might be non-ohmic

179
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but because of how we're
rounding in the measurement,

180
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it actually might give us a change,

181
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especially because our ammeter
is more sensitive here,

182
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and on the other hand, we
might be a situation where

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we are non-ohmic, but it doesn't,

184
00:08:34,123 --> 00:08:36,041
you don't register the
change because it hasn't

185
00:08:36,041 --> 00:08:37,405
been large enough to be registered

186
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by the sensitivity of your instruments.

187
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So, need to be careful,

188
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careful about,

189
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about instrument sensitivity.

190
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Instrument sensitivity.

191
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Sensitivity.

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The rounding,

193
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rounding to nearest,

194
00:09:05,539 --> 00:09:06,956
nearest 0.1 volt

195
00:09:08,312 --> 00:09:09,228
or 0.01 amp

196
00:09:12,505 --> 00:09:13,839
could result in,

197
00:09:17,837 --> 00:09:19,003
in difference

198
00:09:22,100 --> 00:09:23,016
in V over I

199
00:09:24,700 --> 00:09:26,534
when there isn't any,

200
00:09:27,431 --> 00:09:28,764
there isn't any,

201
00:09:31,202 --> 00:09:32,369
or vice versa.

202
00:09:33,582 --> 00:09:35,604
It might not result in a difference,

203
00:09:35,604 --> 00:09:36,840
but there actually might be a change

204
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but it's not big enough to be measured.

205
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Or vice versa.

206
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So you always have to be careful

207
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when you're doing any
experiment in any science

208
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about how sensitive your
actual instruments are

209
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and what the rounding might do

210
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for these calculations.