Hi guys! If you are looking for extra practice questions, I made a huge problem set of my own problems with detailed solutions. Check it at my online shop here: koji.to/k/9uCs
Well done! It is so, so annoying that different exam boards can't agree whether the absolute uncertainty is the smallest graduation, or half the smallest graduation. AQA and Edexcel for example.
@@leuanjennings9929 Yep! AQA uses half of the smallest measurement value (that's what I used at university too when I was in a lab and it's pretty sensible! )
I am so certain about uncertainties now . Thank you so much for this explanation .. those are the parts of this concept that I always cofuse and forget ❤ ( equations containing uncertainties)
Thank you for the explanation! Say you measured a length of wire with diameter: 0.27mm (+-) 0.01mm. And you wanted to divide by 2 to get a value for the radius, what would you do to the uncertainty?
If you are after the radius just divide the value by two but you retain the same uncertainty. So the radius would be 0.135 +- 0.01 mm as you only consider the value you measured.
I'm confused, what reason is there to add or take away, multiply or divide or raise to a power? How do I know which one to do? I don't think I'm getting the "why's". Why are we doing this?
Excellent question! So...absolute uncertainties - we can just add them as we have they have the same units. E.g. mass +mass can gives us kg+kg which is also kg. If we have speed , v=d/t we can't just add meters+seconds in physics. So we convert them to percentages which are dimensionless (unitless). If we raise something to a power, we are essentially using it twice or three times or whatever the power is. e.g. I^2 = I*I so we use it twice, so we multiply the uncertainty by 2. Hope this helps!
Hi sir, i have my physics practical in a few days and i see a lot of questions on estimating the percentage uncertainty. Could you please explain to me how I'd approach this question 🙏
5:00 Even if you are subtracting the total do you subtract the total when working out the percentage uncertainty? So if you wanted to find the extension would the equation for the percentage uncertainty be (Absolute uncertainty /extension) or (absolute uncertainty/ original length + new length)? Thank you
All the theory is covered, I would do lots of practice problems next! I have some here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-vhdI0eZf5nY.html Thanks a lot for the comment! : )
it's microsoft whiteboard which is free, since filming the video though the software has become a lot slower, there might be better alternatives, but it's still quite good!
With your ruler analogy at the start, you state the resolution to be 1mm. Would the absolute uncertainty not then be 0.5mm. You state as much in your note but verbally you said it was still 1mm
interstingly that depends on your exam board. At university I always took the resolution to be half of the smallest measurement, AQA typically does that, OCR in A Level Physics takes to be 1 of the smallest measurement. Hope this helps!
The edexcel spec lists it for a ruler as half the smallest measurement (half the resolution). It also lists the definition of resolution as the smallest reading possible. You can also calculate it as half the range of the data if you are given a lot of measurements and no uncertainty. Hope this helps!
How would you find the percentage uncertainties of an average. For example you're given 5 measurements for the thickness of something and are asked to find the percentage uncertainty given that the measurements are to 3 significant figures
I have actually filmed the answer to this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-WOckc29sZJA.html this link should take you to the correct timing, but have a look at the time stamp, uncertainty of a data set.
@@vaster1142 yep! If you raise it to a power this is equivalent to multiplication, i.e. you have to ad the percentage uncertainty similarly to other rules. Hope this is helpful!
The edexcel spec lists it for a ruler as half the smallest measurement (half the resolution). It also lists the definition of resolution as the smallest reading possible. You can also calculate it as half the range of the data if you are given a lot of measurements and no uncertainty. Hope this helps!
the rules for uncertainties are extremely similar across all a levels : ) yes it is applicable however you should use your specification/syllabus as a checklist when going through this. Hope this helps!
@@zhelyo_physics well my syllabus says students are not expected to compound percentage uncertainties. Is compounding uncertainties same as combining them?
hey I've got this question on my homework that I need help with. it says the uncertainty is 2mm but doesn't say + or - so I'm unsure whether it means +or-1mm or +or-2mm
@@zhelyo_physics but i thought that wasnt the uncertainty i thought that was the value u measure do you still always add it even if the question is substract
Do you mean absolute or percentage uncertainty? As I mentioned we always add uncertainties in both cases. If we add or subtract things we add absolute unc. If we multiply or divide we add percentage unc.
@@erfrerferfrere if we take away the voltage it would be 5-4 = 1V but this is the voltage, not the uncertainty. The uncertainty would still be the same, 1V +- 0.3 V
depends on the problem, think of the fractional uncertainty as a percentage uncertainty and follow the rules in the video depending on the situation : )
Mostly. Around 95% So I design them so that they can be applicable with every exam board. I recommend downloading the specification and ticking concepts as you revise them. Good luck, drop a comment if something doesn't make sense!
I actually have a huge amount out already but will constantly be expanding them - here is a step by step guide for paper 3: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kewwyTfUc_U.htmlsi=ti6V1AVPl35n6M-m Have a browse through the channel, I also have lots of questions from paper 3 and all the content filmed.
