Percentage Error Of A Metre Ruler
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Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top What is the error in a ruler? up vote 2 down vote favorite 2 I'm having trouble understanding simple error analysis of a ruler. Suppose we have this ruler. There is a mark for every centimeter. The precision is half a centimeter. relative error calculator This should mean that the rulermaker guarantees us that about 68% of the time (I don't think this is true in most cases), the true value will be in the interval $(x-0.5 \mathrm{cm}, x+0.5 \mathrm{cm})$. This is because de ruler/marks don't have the exact lenght. If the ruler reads $2\mathrm{cm}$, when it should be $2.5\mathrm{cm}$, what would the error at the $1\mathrm{cm}$ be? If the ruler is a bit too long wouldn't this be reflected for every mark? Is this the correct interpretation of uncertainty? Why isn't there less error when the tip of the object we want to measure coincides with a mark of the ruler? And if we don't measure the object from the tip of the ruler($0\mathrm{cm}$), so we have to calculate the difference, should we have to double the error? experimental-physics error-analysis share|cite|improve this question asked Dec 9 '14 at 23:34 jinawee 6,93132362 I think you're confusing accuracy and precision. The ruler is only precise to within a half cm (to the eye of the user) while it's only as accurate as the spacing was ma
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Community Forums > Physics > General Physics > We've just passed 300 Insights! View them here! What a resource! Dismiss Notice Dismiss Notice Join Physics Forums Today! The friendliest, high quality science and math community on the planet! Everyone who https://www.physicsforums.com/threads/what-is-the-uncertainty-in-a-metre-rule.610200/ loves science is here! WHat is the uncertainty in a metre rule? Page 1 of 3 1 2 3 Next > May 30, 2012 #1 mutineer123 WHat is the uncertainty in a metre rule?? For a single value is it 1 mm or is it 1/2mm(half the smallest division) ? And what about measuring something like a length of a stick (we need to take 2 readings, and deduct them like 15-0=15), then is the uncertainty 1+1=2mm absolute error or is it .5+.5=1mm ? mutineer123, May 30, 2012 Phys.org - latest science and technology news stories on Phys.org •Unusual quantum liquid on crystal surface could inspire future electronics •When quantum scale affects the way atoms emit and absorb particles of light •Nanoantenna lighting-rod effect produces fast optical switches May 30, 2012 #2 K^2 Science Advisor Re: WHat is the uncertainty in a metre rule?? The rule is half the smallest division. So if your percentage error of ruler has 1mm divisions, then the error is 0.5mm. [strike]I believe, the errors do add. So it does sound like 0.5mm+0.5mm = 1mm is the correct answer there, but I'm less certain about that.[/strike] Last edited: May 31, 2012 K^2, May 30, 2012 May 31, 2012 #3 Studiot Re: WHat is the uncertainty in a metre rule?? So it does sound like 0.5mm+0.5mm = 1mm is the correct answer there, but I'm less certain about that. Do you not think it should be [tex]\sqrt {{{\left( {0.5} \right)}^2} + {{\left( {0.5} \right)}^2}} = 0.7mm[/tex] For a single value is it 1 mm or is it 1/2mm(half the smallest division) ? And what about measuring something like a length of a stick (we need to take 2 readings, and deduct them like 15-0=15), then is the uncertainty 1+1=2mm or is it .5+.5=1mm ? That rather depends upon your ruler. If it is a school type ruler which does not have zero at the end of the ruler then yes you have two measurements as above. If it is an engineer's rule with zero flush ground to one end then there is only one comparison to account for. Last edited: May 31, 2012 Studiot, May 31, 2012 May 31, 2012 #4 mfb Insights Author 2015 Award Staff: Mentor Re: WHat is the uncertainty in a metre rule?? I wou
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