Help with percentage uncertainty question for AS physics!Watch

Announcements
#1
A student has a diffraction grating that is marked 3.5x10^3 per m.

Calculate the percentage uncertainty in the number of lines per metre suggested by this marking. (1 mark)

I have seen the mark scheme says it is 2.9%, however i don't know how to get that answer... I got the answer of 0.000029%....
0
3 years ago
#2
(Original post by Smile Generator)
A student has a diffraction grating that is marked 3.5x10^3 per m.

Calculate the percentage uncertainty in the number of lines per metre suggested by this marking. (1 mark)

I have seen the mark scheme says it is 2.9%, however i don't know how to get that answer... I got the answer of 0.000029%....
Can you post the exact question, and your working out pls?
0
3 years ago
#3
Just from what you have given, i assume that you have
1) not taken the factor of into consideration
2) Not multiplied by 100 to get percentage instead of decimal as
.

Besides, what the mark scheme wants is it seems.
0
#4
(Original post by Kyx)
Can you post the exact question, and your working out pls?
That was the exact question.

I did (1/3.5x10^3)x100
0
3 years ago
#5
I'm having trouble finding the absolute uncertainty in the number of lines per metre, for 3.5 x 10^3 lines per metre.
0
2 years ago
#6
To get to the answer, you need to do (100 / 3.5 x 10^3) x 100, which gives you an answer of 2.857142%, which rounds to 2.9%
0
1 year ago
#7
Would that not give you per cm though?
1
4 weeks ago
#8
This same Q is confusing me now as well... surely the mark scheme isnt correct? (1/3.5x10^3)x100 gives 0.029%
0
4 weeks ago
#9
I think the absolute uncertainty implied is 0.1 x 10^3 (ie the value lies between 3.4 and 3.6 x 10^3)
So the % uncertainty would be (0.1 x 10^3) / (3.5 x 10^3) x 100
0
4 weeks ago
#10
(Original post by old_teach)
I think the absolute uncertainty implied is 0.1 x 10^3 (ie the value lies between 3.4 and 3.6 x 10^3)
So the % uncertainty would be (0.1 x 10^3) / (3.5 x 10^3) x 100
But how would you figure out the absolute uncertainty implied from just looking at the question without any extra info? I don't think I'd get that in the exam
0
4 weeks ago
#11
I agree that, to my mind, there is uncertainty as to what to take as the uncertainty!
When values are given to 0.5 (eg a measurement 6.5 cm) I'd assume it's to the nearest 0.5
Here, as it is given to 1 dp (ignoring POT), I'd assume it's to nearest 0.1, but I think it can be taken to plus/minus 0.05.
I expect your teacher can tell you the exam board's rules which you'll need to apply.
A thing that really bugs me is when uncertainty is quoted to lots of sf!
0
4 weeks ago
#12
(Original post by old_teach)
I agree that, to my mind, there is uncertainty as to what to take as the uncertainty!
When values are given to 0.5 (eg a measurement 6.5 cm) I'd assume it's to the nearest 0.5
Here, as it is given to 1 dp (ignoring POT), I'd assume it's to nearest 0.1, but I think it can be taken to plus/minus 0.05.
I expect your teacher can tell you the exam board's rules which you'll need to apply.
A thing that really bugs me is when uncertainty is quoted to lots of sf!
Okay that makes sense actually, thanks for explaining to me and I will take a look at the AQA rules for percentage uncertainties and other related stuff
0
X

new posts
Latest
My Feed

Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

University open days

• SOAS University of London
Wed, 29 May '19
• University of Exeter
Thu, 30 May '19
• Cranfield University
Cranfield Forensic MSc Programme Open Day Postgraduate
Fri, 31 May '19

Poll

Join the discussion

Loved the paper - Feeling positive (195)
22.62%
The paper was reasonable (395)
45.82%
Not feeling great about that exam... (158)
18.33%
It was TERRIBLE (114)
13.23%