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# Help with percentage uncertainty question for AS physics! watch

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%....
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?
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.
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
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.
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%
7. Would that not give you per cm though?

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