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Found 20 results

  1. Aldo

    Uncertainty calculation

    I am calculating for the vitamin C concentration of different fruits and using the formula = Molar mass of vitamin c x concentration of DCPIP x volume of DCPIP used. I am confused on how to search for the uncertainty value. Can someone please help me???? Thank you very much!
  2. Hello everyone, I am doing my ee in physics. I'll get straight into it without wasting anyone's time. So basically in my results after conducting the experiment I have two values for the electron to mass ratio of an electron (e/m ratio). The independent variable was changed in the experiment and it was conducted in two parts therefore leading to two values, one for each part. The values are: 1.96*1011 ±8.63*1010 2.01*1011 ±1.09*1011 Finding the values required using the gradient of the graph results. Therefore to get the errors the uncertainty on the graphs were calculated using the range (largest gradient - smallest gradient) and some propagation of errors was used as well. That was all good. Now, the uncertainty as you can see is very large about 50% for each value. There are reasons for that but that is also ok. First question: To get the discrepancy, I first need an average of the two values. To get the uncertainty on the average I just took the average of the uncertainties (add both and divide by two). Is this correct? Second question: Now that I got the average value I calculated the discrepancy to be 13%. My teacher said that I should check to see if this lies within the %error on my results and if it does then my experiment is accurate. But the problem is I got the %error on the averaged results to be 50%. Does this mean that my results are accurate and not precise? How can it be accurate if the %error is so large, the discrepancy is bound to fall into the range of the error. Hope someone can answer these confusions. I have my ee due in less than two weeks. Sorry for the long post.
  3. Ignacio

    P1 question Nov 2010 help

    Hi there!, Could someone tell me why, the answer to this question is B? I don't understand why the uncertainty of B is higher than A. Thanks!!
  4. Guest

    Uncertainty Calculation

    A burette reading is recorded as 27.70 cm3 +/- 0.05 cm3. Which of the following could be the actual value? I 27.68 II 27.78 III 27.4 A I and II B I and III C II and III D I, II, III I'm not how to solve this, but I used the total error equation to dtermine which one had less of an error - that would be the actual value and I got C. Not sure if it's right?
  5. The graduated cylinder is measured by millimeters, but there is an additional mark that divides each milliliter in half. In other words, between 5 and 10 milliliters, there would be 4 markings. Is the uncertainty recorded to the tenths or the hundredths place?
  6. ibsurvivorhopefully


    is there any easy way of calculating uncertainties with long and tedious formulas? (ex: cylinder V= 1/4 x pi x d2 x h) I've just started IB and uncertainties are confusing me as its only been 3 days and I feel very stressed because i think everyone in my classes finds them really simple
  7. Hehey! thanks for your help I am calculating the number of moles of ascorbic acid. mass = 0.250 +- 0.001 Mr = 176.12 n = mass/Mr = 0.00142 rounded up to 0.001 (to have the same amount of decimal places) (& +- 0.001, because it is dividing by a fixed value with no error). So the percentage uncertainty is 100% ????? hahaha hope not if so I am incredibly screwed
  8. Hey there! so there are maany 'theories' about the number of significant figures and/or decimal places that all the data needs to have. Some say that all the values have to have the same sig. fig. Some say that all the values need to have the same decimal places. Some say that the experimental data should have the same sig fig between them, but not compared to uncertainties. Other say that the uncertainties should have the same amount of decimal places, but not when comparing it to experimental data. Whaat?? So I attach one of the tables (in form of plain text) - it is a minor one, to show what I've done with the values (rounding them up) - I am totally unsure if this is right. (It doesn't show proper calculations or anything - & I'm sure I messed it up with the concentration, it is only to show my understanding of sig. figs). Thanks a lot. IMSOSCREWED so it is like parameter. unit. error. value. mass of ascorbic acid (solute). g. ±0.001. 0.250 volume of water (solution). ml ±0.100. 250 volume of solution used in titration. ml±0.100. 25.0 moles of ascorbic acid. mol ±0.001. 1.44 concentration of ascorbic. mass/volume percent (%). ±0.200. 0.100 agh it's hard to understand without table
  9. Hello IBers, I need help on some things about my chemistry lab: - Let's say I'm measuring how temperature changes over time in a reaction between HCl and Na. Do I have to include an uncertainty for my time? By the way, I was using a vernier lab quest to record this data. - Also, on logger pro, how do I add error bars for my data points using the uncertainty of the temperature probe used in the experiment? I know that the uncertainty of the probe is +/- 0.2 degrees celcius, however, I'm not too sure how to add error bars that also consider the standard deviation. Help would be much appreciated! :)
  10. Hello. I need help with my biology IA. How to calculate the uncertainty for rate of reaction (ml/min)? i know there are two uncertainties, one for the beaker (+/- 0.05) and the other one for the stopwatch (+/- 0.01 min). Do I write both?
  11. Guest

    Quantum Mechanics EE

    Hey everybody, I've been working on my EE, so I'd like to give a brief overview of what I'm doing, maybe if you guys could give me some kind of suggestion/advice? I'm trying to calculate the time it'd take for a pencil to fall when trying to balance it on its point. I'm taking the point of the pencil as an infinitesimally small point. I'll either take it as a cone on a rod, or as a infinitely thin rod with all the mass concentrated at one point (sort of like an unstable pendulum). Classical mechanics suggests that it's possible to put it in (unstable) equilibrium if you get the required initial conditions. The center of mass would have to be directly on top of the base, and obviously it must be at rest. According to quantum mechanics (HUP) those conditions are impossible to reach. I'm thinking of solving an equation of motion, with initial conditions (angle and angular velocity, which ideally should both be zero) restricted by HUP, and then solving for the time it takes to reach a certain angle. I know this is a pretty unspecific overview, but how does this sound? Any suggestions on how to improve? Thanks in advance
  12. DropBoite

    Uncertainty 2

    Had this lying around in my physics folder, very useful!
  13. I have searched the whole internet for weeks, read IB Physics books, and looked everywhere for clues on how to calculate uncertainties in physics, but nothing helps. So lets say this is my data: h, m t1, s t2, s t3, 2 ±0.05 ±0.05 ±0.05 ±0.05 1 0.10 1.35 1.31 1.35 2 0.15 1.72 1.70 1.71 3 0.20 1.99 1.95 2.05 Then when I look for t(ave) I find the averages go like this: 1) 1.34 2) 1.71 3) 2.00 So now when i come to calculating uncertainties what do I do. Since the measurement uncertainty stays the same when you calculate the average of a value I would assume the uncertainties are ±0.05. However, no, that is not what IB wants, basically they want to calculate the uncertainties in the following way: (max.value - min.value)/2. When I do this, I get: 1) 0.02 2) 0.01 3)0.05 The first and second uncertainties are lower than the measurment uncertainity. What do I do now which uncertainty do I use??? t^2 1)1.80 2)2.92 3)4.00 Continuing with other calculations…. We now have to calculate the uncertainties for t^2 and we do it in the following way or so Pearson says: 1) [(t+0.02)^2 - (t-0.02)^2] /2= [(1.34+0.02)^2 - (1.34-0.02)^2] /2= 0.05 2) 0.03 3) 0.20 Using t^2 and h we find g. I know that when you divide or multiply that you convert all uncertainties to percentage uncertainties and add them up. But, my teacher showed us that for g we calculate the uncertainty by finding the residual. The residuals are calculate in the following way: 1) g(ave)-g1= 1.11 2)0.32 3)0.79 The largest residual is the error. g residual 1 g1 19.02 1.11 2 g2 17.59 0.32 3 g3 17.12 0.79 g(ave) 17.91 1.11 (I know the results are far off but that is because the data is fake) At this point I don't know what is happening anymore or what the error is and then I have to find the line with the max gradient by adding the residual to the average result and the line with min gradient by subtracting the residual from the average result. I mean I don't know what the IB expects from us just to miraculously know what they are asking for. I am extremely upset because of this and I hope someone can explain in great detail how to calculate uncertainties properly. I am not submitting my labs untill I figure this out. Thanks in advance
  14. Hey guys, so I am using Photoshop to measure some things for my extended essay with the ruler tool. However, I have been trying to think how to get the uncertainty of the tool as I need it to make the calculations and analyze the data. I have sent an email to my supervisor yet he has not responded me and even searched on the internet hoping that I would get some kind of idea or guide that would help me figure it out.... but nothing, and I have my draft due in a week! I hope any of you guys know anything about this! and if not, thanks anyways! ^^
  15. Hello everyone! I have problem with my Design project in IB Chemistry HL. My research question is: how does the concentration affect the value of experimentally determined enthalpy? I have collected the necessary data, I've created a graph of temperature change versus concentration - it shown the positive linear correlation. After that I have plotted the graph of enthalpy change versus number of moles. As we know, enthalpy is amount of heat changed per mole of a substance. It does not change with the number of moles, it is a constant. Thus, the graph should look in the form y=c, where c=const. Now my question is: How to calculate the uncertainty of that graph? Should I use the equation used in physics that applies for linear graphs: (gradient of f(max)-gradient of f(min)/2? Or should i use sth else? Any ideas? Are we, as the students of IB Chemistry, supposed to calculate the uncertainties of graphs? I've seen a Design Lab Report from chemistry in which the author did not calculate the line of best fit. Neitherless, he got almost maximum points, by the teacher and moderator.
  16. Vioh

    Uncertainty..... Help!

    Hello! I need help with my physics lab report because i have no idea how to work out the uncertainty. If my experiment gives 3 values for 3 different trials: - 340±14 - 350±15 - 360±16 So that the mean would be 350 but what is the uncertainty of the mean? I did google this and found 3 possible ways of doing this: (360 – 340)/2 = 10 (using the range of the all the values) ((360+16) – (340 – 14))/2 = (376 – 326)/2 = 25 (using max and min values) (14 +15 +16)/3 = 15 (using the uncertainties in the values) So what method should I use? Should I quote the answer as 350±10 or 350±25 or 350±15 ? and why? Thanks for your help.
  17. Tsaren


    Hello fellows! I need some help with uncertainty. If the empty crucible weight 27,63g and the crucible with a compound weight 30,72g. What is the uncertainty for the both of them? How do I calculate it , please explain. Thanks for respond!
  18. Hi guys, I'm sorry that the title is a little vague, but I really couldn't come up with anything more clever. So, this is the case: For my lab report I needed to calculate the the acid dissociation constant of an unknown weak monoprotic acid. The values which I could measure were mass (the acid was pure), volume and ph (plus the molar mass of the acid given by the teacher). So to simplify the process, I derived a fancy formula that allows me to do it in one step, instead of going through like five of them (don't worry, I've checked the correctness a million times, so there are no errors in this part). But then I had to calculate the uncertainty for my acid dissociation constant, I got stuck. I have no problems with the uncertainty calculation rules, but my formula has like fractions within fractions and stuff in exponents. I first though that I could avoid the complexity if I just didn't use the formula, but went step by step, and I was wrong, it seemed just as complicated. So I came here to seek help from you people . And the question is: How on earth do I calculate the damn uncertainty for the acid dissociation constant? dx - uncertainty of x m - mass of the acid V - total volume of the solution ph - ph-value of the solution M - Molar mass of the acid (doesn't have an uncertainty because it's provided by the teacher) Here are the values: dm -> +/- 0.001 g, dV -> +/- 0.001 dm^3, d(pH) -> +/- 0.05, M = 46.026 gmol^-1 The formula is in the attachment or here is a download link: http://www.mediafire...3jnei8c16e7khx6. By the way, from reading my explanation, you may see some fundamental errors in how I collected or processed data, this is because I only explained the things relevant to the question, and I would appreciate if your answers would also be focused on the question, and not on the other parts.
  19. engourdis

    Stoichiometry - Chem IA

    Guys, i'm currently in my first year of IB. I have a chemistry IA for titration due tomorrow. I know this is a very simple question but please help! For example I have an equation : H2SO4 + 2NaOH -> 2H2O + Na2SO4 mole of NaOH = 0.05 mols with uncertainty ± 0.01 mols To find the mole of H2SO4 I need to divide 0.05 mols by 2, since the ratio of H2SO4 : NaOH is 1:2. Now what is the uncertainty of the H2SO4??? do i divide it by 2 or is it the same??
  20. aDVnatgae

    Uncertainty question IA

    Hi I have values like 4 grams, 3g,4g,9g,10g I measured this using kitchen scale. It does not say any uncertainty on the scale 1) So should I include uncertainty in the lab report (+- 1g)??? 2) If you are say do the uncertainty, then I have to calculate the mean for these numbers. What do I do? Do I have to first change uncertainties into percent uncertainties, then add them, then turn them back into absolute uncertainties for the final value??? My kitchen scale rounds rumber to nearest whole number

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