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Physics paper 5

9702_s12_qp_52
can someone help me to work out the uncertainty step by step
Original post by djlucifer
9702_s12_qp_52
can someone help me to work out the uncertainty step by step


Can you at least state which question or which part(s) of the question do you need help.
There are a few parts concerning uncertainty.
Reply 2
here i needed help in this to work out the unceertainty step by step
Original post by djlucifer
here i needed help in this to work out the unceertainty step by step


There are at least 2 methods of computing it.

Method 1:


uncertainty = ½ × (maximum value minimum value)


This is a method that will work for A level physics and you should know. I say it will work provided that you do thing correctly.

Δ(1L)=12×(1LΔL1L+ΔL) \Delta \left(\dfrac{1}{L}\right) = \dfrac{1}{2} \times \left( \dfrac{1}{L - \Delta L} - \dfrac{1}{L + \Delta L} \right)

For example, when L = (54.5 ± 0.5) × 10-2 m,


Δ(1L)=12×(1(54.50.5)×1021(54.5+0.5)×102)\Delta \left(\dfrac{1}{L}\right) = \dfrac{1}{2} \times \left( \dfrac{1}{(54.5 - 0.5) \times 10^{-2}} - \dfrac{1}{(54.5 + 0.5) \times 10^{-2}} \right)



Δ(1L)=0.0168 \Delta \left(\dfrac{1}{L}\right) = 0.0168


Method 2:
Assume that you know the following rule:


c=ab c = \dfrac{a}{b}




Δcc=Δaa+Δbb \dfrac{\Delta c}{c} = \dfrac{\Delta a}{a} + \dfrac{\Delta b}{b}


Let a = 1 and b = L in c=ab c = \dfrac{a}{b} ,


Δcc=Δ11+ΔLL \dfrac{\Delta c}{c} = \dfrac{\Delta 1}{1} + \dfrac{\Delta L}{L}



Δcc=0+ΔLL \dfrac{\Delta c}{c} = 0 + \dfrac{\Delta L}{L}



Δcc=ΔLL \dfrac{\Delta c}{c} = \dfrac{\Delta L}{L}


Note that c=1L c = \dfrac{1}{L} ,


Δc=ΔLL×c \Delta c = \dfrac{\Delta L}{L} \times c



Δc=ΔLL×1L \Delta c = \dfrac{\Delta L}{L} \times \dfrac{1}{L}



Δ(1L)=ΔLL2 \Delta \left(\dfrac{1}{L}\right) = \dfrac{\Delta L}{L^2}


Using method 2 for when L = (54.5 ± 0.5) × 10-2 m,


Δ(1L)=0.5×102(54.5×102)2 \Delta \left(\dfrac{1}{L}\right) = \dfrac{ 0.5 \times 10^{-2}}{(54.5 \times 10^{-2})^2}



Δ(1L)=0.0168 \Delta \left(\dfrac{1}{L}\right) = 0.0168


I did not round to the correct significant figures for the uncertainty. Rounding to how many significant figures for the uncertainty is something you should know.

Both methods give the same answer for the uncertainty. Note that you can use a more sophisticated method and the uncertainty may be smaller but it is ok.
Reply 4
Screenshot_2019-01-25 9702 52 AS A Level Physics May June 2018 - 9702_s18_qp_52 pdf.png
can ypu help me to find out the uncertainty here
Original post by djlucifer
Screenshot_2019-01-25 9702 52 AS A Level Physics May June 2018 - 9702_s18_qp_52 pdf.png
can ypu help me to find out the uncertainty here


I hope you can show your attempt first. It is ok to be wrong and this is how you learn. I can say students learn more when they make mistakes.

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