Physics: Post your doubts here!

[qwertypoiu]

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

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

 

[shahzaib9291]

Any idea about physics paper 34

some question on capacitor is coming

 

[The Sarcastic Retard]

some question on capacitor is coming

any more info? I suck at electricity

 

[Shujaat Khan]

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

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!

Its June 2014 (Doesnt get any more recent than that) V22 Q2bii

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!

 

[qwertypoiu]

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!

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.

 

[ahmedish]

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!

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."

 

[ahmedish]

some question on capacitor is coming

good sources you have.

 

[ahmedish]

not that the above is percentage uncertainties.

actual values should be given to a SINGLE sf (without taking into account the zeros.)
the above could also be written as (13 +- 2) x10^2 - hence 1sf

See how the final answer is given at the link there.

can i actually write "(13 +- 2) x10^2 " or does it have to be 13x10^2 and then 2x10^2 since theres a +_ sign between?

 

[ahmedish]

yes you can use (13 +- 2) x10^2.
actually, you should be using it this way

yeah but I mean, they are not on the same like dots?
Like the answer format is like ............ +_ ................
Can I put a big bracket around it then x10^-2?

 

[The Sarcastic Retard]

Ready for paper 22 guys? <3

 

[ahmedish]

Can someone explain precision and accuracy please??\
also long range order and short range order for materials

 

[cambridgewbhs]

Can someone explain precision and accuracy please??\
also long range order and short range order for materials

Precision is how closely repeated measurements of the same quantity agree. It can be thought of as the number of decimal points the quantity is measured to, and is regardless of whether the measurement is correct or not

Accuracy is how close the measurements are to the true value.

 

[qwertypoiu]

Can someone explain precision and accuracy please??\
also long range order and short range order for materials

Long range order is like solids, the particles are aligned for large distances.
Short range order is like liquids. They have some order for a small number of particles, but over larger numbers they aren't perfectly aligned.

 

[ahmedish]

Precision is how closely repeated measurements of the same quantity agree. It can be thought of as the number of decimal points the quantity is measured to, and is regardless of whether the measurement is correct or not

Accuracy is how close the measurements are to the true value.

Yeah I don't get why precision is linked to decimal places? if the values we get for gravity are 9.80 and 9.82, these are precise, what do decimal places have to do with this?

Long range order is like solids, the particles are aligned for large distances.
Short range order is like liquids. They have some order for a small number of particles, but over larger numbers they aren't perfectly aligned.

I mean long range and short range for crystalline, amorphous and polymers

 

[nehaoscar]

Can someone explain this
Its like the Millikan drop experiment
For this I calculated average but the mark scheme simply says that elementary charge is 1.6*10^-19 or 1.7*10^-19 because this is a factor of them all...
But it's not exactly a factor ... So how to do this one??

 

[Saad the Paki]

Please help me solve Q9!

 

[chocolatelover]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w09_qp_22.pdf
Q5 part b. idk why the mark scheme says that the phase difference is 180.

 

[The Sarcastic Retard]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w09_qp_22.pdf
Q5 part b. idk why the mark scheme says that the phase difference is 180.

Hope this pic helps u to understand this concept.
Good luck.

 

[qwertypoiu]

Please help me solve Q9!View attachment 57255

So there are two parts to this race:
1. Increasing speed from 0 to 10
2. Going at constant speed of 10

We can find time taken for both, and add them up.

1. u=0, v=10, a=2.5, s=?, t=?
First let's find distance covered:
v^2 = u^2 + 2as
100 = 0 + 2(2.5)s
s=20m
So he covered 20m.
Also time taken:
v=u+at
10=0+2.5*t
t=4s
So he took 4s

2. Since he covered 20m in first section, he has to complete 80m more. (100-20)
time = distance / speed = 80/10=8s

Total time = 4 + 8 = 12s

 

[Saad the Paki]

So there are two parts to this race:
1. Increasing speed from 0 to 10
2. Going at constant speed of 10

We can find time taken for both, and add them up.

1. u=0, v=10, a=2.5, s=?, t=?
First let's find distance covered:
v^2 = u^2 + 2as
100 = 0 + 2(2.5)s
s=20m
So he covered 20m.
Also time taken:
v=u+at
10=0+2.5*t
t=4s
So he took 4s

2. Since he covered 20m in first section, he has to complete 80m more. (100-20)
time = distance / speed = 80/10=8s

Total time = 4 + 8 = 12s

Oh thank you so much!
Would appreciate it if u could help in this one as well ( Q6 )