A level physics help! exam in 2 days!!

so i knew the answer would be B or C but couldnt decide which one and it was B but i dont know why because wouldnt both reading just cause an uncertainty of 2% in the final calculations? unless micrometers have an uncertainty when lining up the micrometer?

(edited 11 months ago)

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Reply 1

gliz

Original post by FM1/FP1

i was stuck on this question recently and like you i narrowed it down to B or C, the only reason i could come up with for the answer not being C is that the distance you are measuring in C (length), is greater than the distance you measure in B (diameter), and ive always been told in school that the larger the measurement the lower the percentage uncertainty, and i assumed this correlates with standard uncertainty, so therefore the uncertainty in C is less since the measurement your taking is larger. not sure if my reasoning is entirely correct but i hope I've helped

Reply 2

Joinedup

you're going to be interested in the cross sectional area of the wire - which means you are going to be squaring the radius.

the rule for raising a measured value to a power is that you multiply the percent uncertainty by the power.

https://pmt.physicsandmathstutor.com/download/Physics/A-level/Notes/AQA/Practical-Skills/Uncertainties%20and%20Methods.pdf

Reply 3

user8937264980

You're gonna square (d/2) to get A. Therefore the uncertainty of diameter is x2.
V/I gives R, both V and I are to the power of 1 so uncertainity isn't multiplied.
Length is also just L in the resistivity equation so again uncertainty isn't multipled.