The error-analysis tag has no wiki summary.
5
votes
3answers
918 views
How to combine measurement error with statistic error
We have to measure a period of an oscillation. We are to take the time it takes for 50 oscillations multiple times.
I know that I will have a $\Delta t = 0.1 \, \mathrm s$ because of my reaction ...
4
votes
5answers
359 views
The approximate uncertainty in $r$
The volume of a cylinder is given by the expression
$V=\pi r^2 h$
The uncertainties for $V$ and $h$ are as shown below
$\begin{align}
V&\pm 7\%\\
h&\pm 3\%
\end{align}$
What is the ...
4
votes
2answers
173 views
Why propagation of uncertainty is linear?
I'm in doubt with one thing: let's imagine that we have $n+1$ quantities, $n$ of them being directly measured, and the other one being related to the first $n$ by a function $f : \mathbb{R}^n \to ...
4
votes
2answers
100 views
Do you round off insignificant digits in the middle of a calculation?
I have a question... Do you round with significant digits during each subcalculation of a problem or only when the entire problem is complete?
Example:
multiply the following number:
$$1.8 \times ...
4
votes
2answers
733 views
Wheatstone bridge galvanometer error
We had to measure the resistance of $R_x$, we balanced the Wheatstone bridge and did calculations. My question is: we didn't include galvanometer error into calculations. Why is that? I read that it's ...
3
votes
3answers
354 views
Calculating uncertainties for a final result
Say you are dividing 2 times with uncertainties:
$$\frac{t_1}{t_2} ~=~ \frac{0.551s \pm 0.002s}{ 0.712s \pm 0.002s}.$$
After doing the calculations you get:
$$\frac{t_1}{t_2} ~=~ 0.774 \pm ...
3
votes
1answer
990 views
How to combine the error of two independent measurements of the same quantity?
I have measured $k_1$ and $k_2$ in two measurements and then I calculated $\Delta k_1$ and $\Delta k_2$. Now I want to calculate $k$ and $\Delta k$.
$k$ is just the mean of $k_1$ and $k_2$. I thought ...
3
votes
2answers
122 views
Question about uncertainty
Are $3.43\pm 0.04$ $\frac{\mathrm{m}}{\mathrm{s}}$ and $3.48$ $\frac{\mathrm{m}}{\mathrm{s}}$ within expected range of values?
The answer is yes, but I do not clearly see why this is so. I appreciate ...
2
votes
2answers
118 views
When do I apply Significant figures in physics calculations?
I'm a little confused as to when to use significant figures for my physics class. For example, I'm asked to find the average speed of a race car that travels around a circular track with a radius of ...
2
votes
1answer
239 views
Is $\sigma$ or $\sigma / \sqrt{N}$ is error of a measurement?
I wonder whether $\sigma$ or $\sigma / \sqrt{N}$ is error of a measurement. When I measure, say $0, 1, -1, 1, -1$, I have a $\sigma = 1$. I just measure $0, 1, -1$, I also have $\sigma = 1$.
But in ...
2
votes
2answers
575 views
Calculating uncertainty in the final result (combining uncertainties)
I'm struggling to determine the uncertainty in $F$ so it would match the textbook answer.
The problem statement is: A force F is obtained using the equation: $F = \frac{mv^2}{2\pi(x_2 - x_1)}$.
The ...
2
votes
3answers
2k views
Wheatstone Bridge
Why is using a Wheatstone bridge such an accurate way of calculating an unknown resistance? What are the benefits of using it over Ohm's law?
It seems that it has something to do with the wires ...
2
votes
1answer
73 views
Experimental measurement of volumetric flow rate
The other day I with my team had to measure the volumetric flow rate through a pipe only using a 2000 mm$^3$ volumetric flask and a chronometer. The end of the pipe discharged to the atmosphere. As we ...
2
votes
2answers
48 views
Asymmetric uncertainties
Inspired by these two question on tex.SX
Asymmetrical tolerancing
Asymmetric uncertainties with siunitx package
I'd like to ask for a nice explanation for these kind of uncertainties, like ...
2
votes
1answer
52 views
Multimeter has a resistance
If a multimeter has a resistance (1M ohm, say) when measuring voltages how do I take that into account in my error?
2
votes
2answers
228 views
Multiple measurements of the same quantity - combining uncertainties
I have a number of measurements of the same quantity (in this case, the speed of sound in a material). Each of these measurements has their own uncertainty.
$$ v_{1} \pm \Delta v_{1} $$
$$ v_{2} \pm ...
2
votes
0answers
43 views
Definition of Significant Figures
In my textbooks, significant figures are defined as:
“Significant figures by definition are the reliable digits in a number that are known with certainty.”
“A significant figure is the one ...
2
votes
0answers
28 views
error propagation and collision in ideal gas
When dealing with gas, a statistical approach is needed because
For N particles, you have to solve 6N equations which cant be done analytically. To know our time step for numerical solving, you can ...
2
votes
0answers
143 views
Production vs. Collection, and Contaminants vs. Depositions, what might be missing in cold fusion research
I though cold fusion and LENR were discredited, but just a few days ago I found out that NASA is claiming LENR is real. So I thought if they're detecting something, what could it be, and why wasn't it ...
2
votes
1answer
56 views
Is this the correct way to I combine multiple interdependant pressure readings?
I want to measure the density in different layers of a suspension. To do this I want to place pressure sensors at different heights. Let's assume that the sensors are not by orders of magnitude more ...
2
votes
0answers
351 views
How to calculate uncertainties of a natural exponential function?
(I apologize if this should be posted in mathematics, however I chose to post it here as it's technically about physics)
I conducted an experiment in which position of items were shifted on an ...
2
votes
0answers
138 views
How do I do error calculus right using gnuplot as an example?
Given is a set of measurements with their respective errors for example an energy spectrum. In gnuplot one is to fit a function $ f(x;\{p_i\})$ depending on a variable $x$ and on fit parameters $p_i$. ...
1
vote
1answer
39 views
Measurement uncertainty of the quantity, that is function of two others quantities
I'm trying to compute uncertainty for the density of the ball.
I measured its radius 6 times, so I was able to compute the stastistical uncertainty (we call it uncertainty type A, I don't know, if ...
1
vote
3answers
111 views
Error calculation with linear regression
I am trying to determine the boltzmann constant by using a bipolar junction transistor.
In my circuit (apparently I don't have enough point to join a image sorry), the Ebers and Moll model gives the ...
1
vote
1answer
77 views
Calculating uncertinity in measurements [closed]
I have a question relating to uncertinity.The equation used is period of a pendulum.
T=2π √(l/g)
For example consider time to complete 10 cycles by the pendulum as 19.6 (+/- 0.2)s.
I want to know ...
1
vote
1answer
82 views
Variance of Nested Experimental Uncertainty
I have to find the uncertainty of a quantity $Q$ doing two mean values. For example for a set of parameters I measure ten times $Q$, I obtain a mean value $Q_1$ and variance ${\rm Var}(Q_1)$. Then for ...
1
vote
1answer
494 views
Calculating the Uncertainty for an Average Value [closed]
How would I calculate the uncertainty for the average of this set?
$32.5 \pm 0.1$
$32.0 \pm 0.1$
$32.3 \pm 0.1$
1
vote
1answer
58 views
center of mass error - calculating systematic error in change in PE
Suppose we have to calculate systematic error in change in PE. Let's suppose systematic error due to scale is 1%. I'm confused about the center of mass error.
\begin{align}
\Delta PE = m*g*h_1 - ...
0
votes
1answer
96 views
How can constants… change?
I recently noticed that the value of Planck's constant has changed on Wikipedia. The value that I had in mind (from Google), $6.626068\cdot{}10^{-34}\text{J.s}$, has changed to ...
0
votes
3answers
227 views
Significant Figures
Subtract 0.2 J from 7.26 J. Express your answer to the correct number of significant figures for the given data.
I think its 7, but the answer is 7.1. HOW?
0
votes
1answer
249 views
Two cylinders with same volume but different dimensions
If there are two cylinders (A and B) both with the same volume. B's radius is half of A's, so the length of B must be 4 ($2^2$) times that of A.
The uncertainty for the radius of A is the same as ...
0
votes
1answer
54 views
How can I cheat an XRD sample (~10 mg) from a total 1g required? How can I use for the background.
How much can affect (in terms of hump) my X-ray diffraction pattern the "amorphous" glass or maybe someone can suggest me other material to compensate for the small amount of the sample.
Note: my ...
0
votes
1answer
101 views
Is it possible to measure the true distance between two objects? [closed]
Could we measure an accurate distance between two objects or do we get a number with an infinite amount of decimals? A number with an infinite number of decimals are an infinite amount of data, so I ...
0
votes
0answers
11 views
Error bars for pair-correlation function [migrated]
I have obtained some data from neutron diffraction for some material samples. The "rawest" form of the data is the structure function $S(Q)$.
We can choose a variety of different Q-maxes when ...
0
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0answers
31 views
Modern Physics/Theoretical Uncertainty? [closed]
A bumblebee is flying around your kitchen with an average speed of 5.0 m/s. You very carefully measure its position to be 3.01 m in the x direction, 0.25m in the y direction, and 1.23 m in the z ...
0
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0answers
44 views
About the resolution/$\sqrt{12}$ uncertainty
Suppose you want to measure a (real-valued) quantity with an apparatus which will return as a result of the measurement the closest integer to the true value of the quantity.
Then, a common use is to ...
0
votes
1answer
48 views
Statistical error in a regression
I measured some voltage values ($x$) and some corresponding frequencies ($y$). I know that the voltage can only be measured within an uncertainty $\Delta x$. And the uncertainty of $y$ shall be ...
0
votes
0answers
260 views
Error Analysis, Change in momentum, Kinetic Energy
If momentum of an object is increased by 10%,then its kinetic energy will be increased by?
Well, I don't need the solution logically by calculating the change in Kinetic Energy etc, but my question ...
0
votes
0answers
49 views
Piezoelectrical effect in a pendulum
How can I compute the piezo-electrical effect of a pendulum of frequency $f$ and amplitude $R$? What constants of the material will enter the computation?
The material in question is an electrode on ...
-2
votes
0answers
14 views
Assign different absolute/fractional uncertainties for each data point, Excel, graphs [closed]
I have tried to find information about how it is possible to assign different uncertainties for each data point (using error bars) using Excel, but I cannot really figure out how that is possible. I ...
-3
votes
1answer
39 views
How many measurements should be done? [closed]
I am measuring time of a computer operation. The operation should run roughly same time each time I measure it. How many times should I measure it to get good average and standard deviation?
