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Physics: Post your doubts here!

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ahmedish

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If i have a value of 6453 and uncertainty of 5%
how should I write the final answer?
6400+_ 300?
I got this as 5% of 6453 is 322.65, to 1 s.f is 300
then i got 6400 as in to the same "tens" like thats 3 hundred, so the value should be to the hundreds and is 6400
bc in ones with decimal if the uncertainty is 0.4 we write the value to 1 dp
is this correct?
 
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ashcull14

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upload_2015-10-9_20-19-22.png
(c) On Fig.4.1, mark a position of the pivot P for the piston to have
(i) maximum speed (mark this position S), [1]
(ii) maximum acceleration (mark this position A).
 
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Shujaat Khan

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P
ashcull14 said:
View attachment 57183
(c) On Fig.4.1, mark a position of the pivot P for the piston to have
(i) maximum speed (mark this position S), [1]
(ii) maximum acceleration (mark this position A).
Click to expand...
According to me max speed should be half sphere end horizontal at either left or right. Think of it as an shm max kinetic energy is always at equilibrium position.

As for acceleration half sphere vertical logically( up or down)
 
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Shujaat Khan

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ahmedish said:
If i have a value of 6453 and uncertainty of 5%
how should I write the final answer?
6400+_ 300?
I got this as 5% of 6453 is 322.65, to 1 s.f is 300
then i got 6400 as in to the same "tens" like thats 3 hundred, so the value should be to the hundreds and is 6400
bc in ones with decimal if the uncertainty is 0.4 we write the value to 1 dp
is this correct?
Click to expand...
Why not use power10.
(6.45+- 0.323)*10^3
Or to 2sf both as you seem fit
 
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ahmedish

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Shujaat Khan

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ahmedish

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Shujaat Khan said:
Strange. Either my physics teacher was in the wrong or years have changed and so did answers? I need to confirm this with more teachers and friends , could you provide me the question for the "attached" screenshot?
Also thanks for the info really didnt know about this throughout 2years I've been using 2sf
Click to expand...
Its June 2014 (Doesnt get any more recent than that) V22 Q2bii
 
qwertypoiu

qwertypoiu

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Shujaat Khan said:
That's so wrong! Who told you that? Don't do that mistake in exams they will penalize you for this.
You never came across an uncertainty with +- 0.25 or +-1.5 in any question paper? You must keep working more papers then.
These are 2s.f btw

More info here http://facultyfiles.deanza.edu/gems/lunaeduardo/UncertaintyandSignificantFig.pdf
Click to expand...
It's funny because the document you've linked to says this:

"Experimental uncertainties should be stated to 1-significant figure."

I can also confirm this, uncertainties should be stated to 1 sig from what I learnt last year in AS
 
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qwertypoiu said:
It's funny because the document you've linked to says this:

"Experimental uncertainties should be stated to 1-significant figure."

I can also confirm this, uncertainties should be stated to 1 sig from what I learnt last year in AS
Click to expand...

Experimental uncertainties.... It's for practical ones( using meter rule etc...) I was referring to second part of explanation.
Obviously experimental uncertainties should be to 1sf, cause you can't read more than 0.1 on a meter rule lol( or other instruments such as micrometer, protractor).

I copied the extract if you really didn't understand which part I pointed out..
"Rule For Stating Answers – The last significant figure in any answer should be in the same place as the uncertainty. Ex. a = 1261.29 ± 200 cm/s2 a = 1300 ± 200 cm/s2 (correct)"

Notice how +-200 is written to 3sf, yes every 0 that comes AFTER a number counts as an additional sf!

ahmedish said:
Its June 2014 (Doesnt get any more recent than that) V22 Q2bii
Click to expand...

Do you perhaps have another question? This one doesn't prove anything, EVERY SINGLE MEASUREMENT IN THE QUESTION WAS TO 1s.f so obviously the answer should be to one s.f unless students do not have common sense.
Try and see if you can find a question which involves 2 or more sf in the QUESTION ITSELF!
e.g of what I mean: 0.92 g +-0.11g

Also look at what The Physicist posted, http://physics-ref.blogspot.com/2014/11/9702-november-2009-paper-22-worked.html
He uses 2sf when getting answer for uncertainty quote:" % uncertainty in g = 1.09% + 2(1.55%) = EITHER 4.2%OR 4.3%"

I will be sure by tommorow to ask my physics teacher for a clear answer!
 
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qwertypoiu

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Shujaat Khan said:
Experimental uncertainties.... It's for practical ones( using meter rule etc...) I was referring to second part of explanation.
Obviously experimental uncertainties should be to 1sf, cause you can't read more than 0.1 on a meter rule lol( or other instruments such as micrometer, protractor).

I copied the extract if you really didn't understand which part I pointed out..
"Rule For Stating Answers – The last significant figure in any answer should be in the same place as the uncertainty. Ex. a = 1261.29 ± 200 cm/s2 a = 1300 ± 200 cm/s2 (correct)"

Notice how +-200 is written to 3sf, yes every 0 that comes AFTER a number counts as an additional sf!



Do you perhaps have another question? This one doesn't prove anything, EVERY SINGLE MEASUREMENT IN THE QUESTION WAS TO 1s.f so obviously the answer should be to one s.f unless students do not have common sense.
Try and see if you can find a question which involves 2 or more sf in the QUESTION ITSELF!
e.g of what I mean: 0.92 g +-0.11g

Also look at what The Physicist posted, http://physics-ref.blogspot.com/2014/11/9702-november-2009-paper-22-worked.html
He uses 2sf when getting answer for uncertainty quote:" % uncertainty in g = 1.09% + 2(1.55%) = EITHER 4.2%OR 4.3%"

I will be sure by tommorow to ask my physics teacher for a clear answer!
Click to expand...

When you say 200 has three significant figures, you're making a mistake.

200 is ambiguous, it could be considered to be having 1 sig, 2 sig, or 3 sig. To make it clear, it may be written as follows:

1 sig: 2 x 10^2
2 sig: 2.0 x 10^2
3 sig: 2.00 x 10^2

I hope the difference is clear, 200 was intended to have 1 sig in that paper of yours.
 
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ahmedish

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Shujaat Khan said:
Experimental uncertainties.... It's for practical ones( using meter rule etc...) I was referring to second part of explanation.
Obviously experimental uncertainties should be to 1sf, cause you can't read more than 0.1 on a meter rule lol( or other instruments such as micrometer, protractor).

I copied the extract if you really didn't understand which part I pointed out..
"Rule For Stating Answers – The last significant figure in any answer should be in the same place as the uncertainty. Ex. a = 1261.29 ± 200 cm/s2 a = 1300 ± 200 cm/s2 (correct)"

Notice how +-200 is written to 3sf, yes every 0 that comes AFTER a number counts as an additional sf!



Do you perhaps have another question? This one doesn't prove anything, EVERY SINGLE MEASUREMENT IN THE QUESTION WAS TO 1s.f so obviously the answer should be to one s.f unless students do not have common sense.
Try and see if you can find a question which involves 2 or more sf in the QUESTION ITSELF!
e.g of what I mean: 0.92 g +-0.11g

Also look at what The Physicist posted, http://physics-ref.blogspot.com/2014/11/9702-november-2009-paper-22-worked.html
He uses 2sf when getting answer for uncertainty quote:" % uncertainty in g = 1.09% + 2(1.55%) = EITHER 4.2%OR 4.3%"

I will be sure by tommorow to ask my physics teacher for a clear answer!
Click to expand...
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w12_ms_21.pdf
here you go lad, 2)c) values to 2 s.f
uncertainty to 1 leading to 1 d.p so value of R given to 1 d.p
someone correct me if im wrong, HOWEVER I believe the examiner report backs me up on this one. "The correct value for the resistance was calculated by a significant number of candidates. The
calculation of the uncertainty in R was not calculated correctly by the vast majority. A very small
number were able to state the value for R with a correct number of significant figures determined
by the uncertainty value."
 
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