Okay, I think this video is causing a bit of confusion now xD
https://www.youtube.com/watch?v=MwzDPhV6dlY&list=PLlDtVvefFYT-LUGAGJ1aL-mwE4ngGhN7M&index=3When he's measuring using the ruler he takes a +/- 0.5mm error at the start... I don't understand why since the ruler starts exactly at zero as with a metre rule?
Okay theres a comment on this lol
question: Is there always uncertainty at the start of a measurement?
answer: Excellent question (and one that is still very much open to debate). The latest info I received directly from the exam board is that for a digital instrument then there isn't an error at the start of the measurement
Also if you skip ahead to where he pulls out the digital caliper, he has an error of +/- 0.01 mm. I understand that the digital caliper increments by 0.01mm, so shouldn't the uncertainty read +/- 0.005 mm? Okay wait, in the comments section someone asks about this.
question:
But why if the voltmeter and stopwatch can read 0.01 is the uncertainty 0.01? Shouldn't it be 0.005? I don't understand, is the uncertainty just the smallest measurement then?
answer: My understanding (especially based on the way the OCR look at uncertainties) is that for an analogue scale the uncertainty is to half the smallest scale division which in the case of a ruler is +/- 0.5 mm at each end so +/-1mm like you said. For a digital scale the uncertainty is the smallest scale division on the measuring instrument. That's the guidance I was given when I queried this with the exam board and that is what they are expecting students to use.
Sorry about this... Maybe I'm picking from too many sources xD I do AQA and the video is customised to OCR. :/ how do i find out what AQA wants? My Physics teacher is a bit of a round about person.. he'll tell you a bunch of stuff and somehow manage to avoid answering the question xD
EDIT: Nope wait, I have a handbook from AQA that I foudn online, it reads:
When measuring length two uncertainties must be included. The uncertainty of the placement of zero of the ruler adn the uncertaintity of the point the measurement is taken from. As both endes of the ruler have a +/- 0.5 scale division uncertainty the measurement will have an uncertainty of +/- 1 division. For most rulers this will mean it has an uncertainty of +/1 division.
Sorry to trouble you! Found the answers...
To summarise:
For AQA, theres always a +/- 0.5 scale division uncertainty at the beginning as well. I assume this applies for a metre rule too.
With regards to digital tools, AQA's handbook doesnt say anything on this BUT, it does say: "Measurement are often written with the uncertainty. An example of this would be to write a voltage was (2.40 +/- 0.005) V. So they half the uncertainty? Not entirely clear on this but I will ask my teacher