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Found 12 results

  1. Hi~ I am writing my physics IA, and have come across a problem: I have data for six trials, and when I am calculating the uncertainty of its average values, which of the two methods should I use?: 1. (max-min)/2 method 2. standard deviation Should I use the first method or the second method for my average uncertainty for six trials? Which one is the method that is generally approved by IB and is capable of getting a level 7 in the internal assessment? Thank you!!
  2. I have my Physics exam tomorrow and I have a few questions in various chapters. Measurements and uncertainties: If in a calculation, I find the answer to be 500, but the numbers that I used all have 3 significant figures, would I be able to give the answer as 500? Does that have 3 significant figures? Or would the answer be 5 x 102 ? When finding the absolute uncertainty with the percentage or maximum/minimum method, what are some rules that apply here? In my notes I wrote down that if there is addition or subtraction in the original equation, then I must add the absolute uncertainties. But when there is multiplication, division or indices, then I must add the percentage uncertainties. Is this correct? Kinematics: I'm really confused about a question in a Paper 1. "A constant horizontal force FA is applied to a block m1. Block m1 is in contact with a separate block m2. The blocks remain in contact as they accelerate along a horizontal frictionless surface. m1 has a greater mass than m2. Air resistance is negligible. Which statement is correct?" So I picked D which was "The force that m1 exerts on m2 is equal to F", but I was wrong and the actual answer was B "The force that m1 exerts on m2 is less than F". Why is that? Thermal physics: I would appreciate any common examples/questions involving the method of mixtures, since I haven't succeeded in solving one yet. By method of mixtures, I mean mcΔθ = mLf + mcΔθ. Would this equation work in every situation or should I be careful? Circular motion and gravitation: For g = F/m, if you have a satellite orbiting a planet, is 'm' the mass of the satellite or the planet? For tanθ = v2/Rg, what does 'R' represent? Is it the normal force or the molar gas constant? Also, when you write ' -g', does that equal -9.81 ms-2 or +9.81 ms-2 ? General: Does uppercase P stand for power and lowercase p stand for pressure? Also, how should I approach ratio questions?? I sometimes get them right but sometimes not. What should I start with?
  3. The real value of g found is (9.807 +/- 0.7) ms^-2 In an experiment, the value is found to be (10.4 +/- 0.7) ms^-2 State, with a reason, whether the experiment is accurate.
  4. Hey guys so it's time to calculate uncertainties for the IA which is due in two days. My teacher has told us that there is new uncertainties calculations for the new 2016 syllabus, although I searched videos/syllabus/forum posts and could not find any evidence of this. So what she said was: Old syllabus: For adding or subtracting A and B, you add or subtract uncertainties of A and B. Multiplying or dividing, you calculate percent uncertainties. New syllabus (what we should be doing): Adding and subtracting A and B: Square uncertainties of A, square uncertainties of B, add them together, and square root the whole thing. Multiplying and dividing A and B: Take the standard deviation of uncertainties, or divide uncertainty of A by value of A, square it, divide uncertainty of B by value of B, add them, and square root the whole thing. My calculations: 10.0 +/- 0.05 (volume in a pipette) divided by 10.70 +/- 0.01 (time using stopwatch app on the phone) 10.0/10.91 and 10.0/11.46 using the same uncertainties. I then need to take an average of these three results. Which way should I be calculating uncertainties? Are there actually changes in calculating them in the new syllabus? I am inclined to think I should be doing the 'old syllabus' way because otherwise, taking an average of uncertainties requires more tedious work (a lot of squaring and square roots). Thank you!
  5. Hi guys, I'm at the end of my first year and I've pretty much finished my biology IA except when I got to the uncertainties I realised that I had no idea how to go about doing them! Throughout the year I kind of just wrote whatever I thought they were and got partial marks (I realise now, not the best scoring technique) If anyone could give me a step by step breakdown of how to tackle the uncertainties in a biology IA that would really, be so appreciated. Thank you so much!
  6. I'm doing my chemistry IP (previously known as IA) using a simulation, since its difficult to perform the experiment in the lab. What uncertainties could be there in this case and how to improve them?
  7. Hi, I'm having trouble calculating the uncertainties in an average value. I have obtained several values for VIt (Voltage x Current x Time) and wish to average the values. How do I calculate the uncertainty in the average value of VIt? The issue I'm having is that each value of VIt has a different uncertainty. How do you calculate the uncertainty in the average value if each value has a different uncertainty? Thanks, abarnes98
  8. I have a question regarding uncertainties as I don't really know how to find them. I have a question referring to grams of a substance and also mmHg, as in for blood pressure. So I would have 'g' for one unit. I would also have 'mmHg' for another unit. But what would be the uncertainty value for this or is there even any...? Thanks for any help offered. Note: I am doing a practice lab and just stating my units in the beginning. So the uncertainties would be +/- (whatever it is). I currently have mine set to both +/- 1 but I don't know if it is correct.
  9. Hey I'm in my first year of HL Chem and I just cant seem to understand uncertainties. Could someone explain them to me please?? Thank you soooooooooo much!
  10. Hey guys, I'm doing an IA and I'm stuck on one section. If I have a variable a on my y - axis, and the uncertainty was a ± 0.003, how would I calculate the uncertainty if my y- axis was transformed to ln(a)? How would I propagate my uncertainties if I applied a natural log function? Thank you!
  11. Hey Guys, For AGES, our class has been having disputes about how the average uncertainty is calculated in physics. Here are 2 options that we are confused between So if we want to know the Avg uncertainty and values are 44.3 ± 0.2 , 44.7 ± 0.2, 44.9 ± 0.2 and 44.1± 0.2 1) Average uncertainty = (Max value - Min value)/Total number of values Avg uncertainty = (44.9-44.1)/4 We got this from an IB Physics uncertainties book... I can't remember how old it was but i think maybe around 2007 or more recent. But this seems outrageous! You honestly can't just do that can you?!?! 2) We think it should be the way we do it in chem and maths and everywhere else! Avg uncert = Total sum of uncertainties/Total number of values taken Avg uncert = (4*0.2)/4 Avg uncert = 0.2 ! This is sooo much more logical. And at the same time they say that you need to take the greater uncert value, which is just 2 in this case. The problem is that method 1 gives you the same uncertainty (±0.2) in this example, but in various other problems that we have had in class it gives a greater uncertainty than ± 0.2 and it is illogical to use a greater value as the uncertainty. How do you guys calculate Average Uncertainties?
  12. Guest

    Chemistry lab uncertainty help?

    I'm doing an experiment and have these values: Initial temperature: 21.0°C ± 0.5°C Final temperature: 63.0°C ± 0.5°C (1st trial) 60.0°C ± 0.5°C (2nd trial) So the average change in temperature is 40.5°C. Now I need help with my uncertainties. I'm not sure how to find it out. Do I just add all the uncertainties and get ± 2? Please help me
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