# Uncertainties Definition and 12 Discussions

In metrology, measurement uncertainty is the expression of the statistical dispersion of the values attributed to a measured quantity. All measurements are subject to uncertainty and a measurement result is complete only when it is accompanied by a statement of the associated uncertainty, such as the standard deviation. By international agreement, this uncertainty has a probabilistic basis and reflects incomplete knowledge of the quantity value. It is a non-negative parameter.The measurement uncertainty is often taken as the standard deviation of a state-of-knowledge probability distribution over the possible values that could be attributed to a measured quantity. Relative uncertainty is the measurement uncertainty relative to the magnitude of a particular single choice for the value for the measured quantity, when this choice is nonzero. This particular single choice is usually called the measured value, which may be optimal in some well-defined sense (e.g., a mean, median, or mode). Thus, the relative measurement uncertainty is the measurement uncertainty divided by the absolute value of the measured value, when the measured value is not zero.

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1. ### Uncertainties in a set of measurements

Suppose I measure the distance between two objects for three trials. The two objects then get farther away, and I measure the distance between them again for three trials. I repeat this for 3 more different distances, getting a total of 15 measurements (3 trials for 5 distances). I then compute...
2. ### How do I find refractive index uncertainties?

I've been doing an experiment where I've used prisms and a spectrometer to find the exact angles inside the prisms and the refractive index of the prisms by finding the minimum angle of deviation. I have attached a picture of the formula I've been using to find the refractive indices. Where...
3. ### Uncertainty of the function? My answer is a bit different

Homework Statement Homework Equations The Attempt at a Solution The answer is different though,
4. ### B Can %age uncertainty in value ever be greater than 100?

We were given an experiment in which the %age uncertainty of majority of students happened to be greater than 100?
5. ### How to calculate the average with uncertainties?

Homework Statement How to calculate the average given the uncertainties in each measurement 8.70 +/- 0.28, 9.680 +/- 0.046, 9.700 +/- 0.055, 9.720 +/- 0.067? Homework Equations The Attempt at a Solution I know I add the values and divide by 4. I also know I add the absolute uncertainties but...
6. ### Uncertainty problem

Homework Statement A common method for finding wavelength is to use diffraction grating. The relationship between wavelength λ and the angle of max intensity θ for first order interference is λ = d*sinθ where d is the spacing between lines on the grating, which is the inverse of the grating...
7. ### I Calculating semi-major axis and minimum mass of an exoplanet

Hello guys, I'm doing my physics coursework on kepler's third law and I'm finding the minimum mass and semi-major axis of a unknown planet. I have the following data: Stellar mass Mstar = 1.31 ± 0.05 Msun Orbital period P = 2.243752 ± 0.00005 days Radial velocity semi-amplitude: V = 993.0 ±...
8. ### Uncertainty of frequency

what can be the uncertainty of the frequency that humans can hear ? I'm aware that there are many ways,but i tried google-ing to find them but i couldnt. if you could help me it would be great.
9. ### Signal to noise ratio and uncertainty in magnitude

1. The problem statement, all variables and given/known dat Show that if you have a signal f and noise σf for a stellar flux measurement, then the uncertainty on the observed magnitude is given by σm = 1.0875 x σf / f Homework Equations (you should use the fact that when ε<<1 then log(1±ε) ≈...
10. ### Expected value of x^2

Homework Statement My teacher made up this question, but I think there's something wrong. Consider the wave packet in momentum representation defined by Φ(p)=N if -P/2<p<P/2 and Φ(p)=0 at any other point. Determine Ψ(x) and uncertainties Δp and Δx. Homework Equations Fourier trick and...
11. ### Error Propagation

Homework Statement Suppose you measure three numbers as follows: Homework Equations x= 200. +-2. y= 50. +-2. z= 40. +-2. where the three uncertainties are independent and random. Use step-by-step propagation to find the quantity q= x/(y-z) with its uncertainty. The Attempt at a...
12. ### Error Propagation help?

Homework Statement I am given a frequency value of 95 GHz (9.5x10^10 Hz), C= 25 F, L=1.12x10^(-25) H. The question is to find the uncertainties in frequency by taking account of inductor being 5% accurate & capacitor being 8% accurate. Homework Equations I believe this is the correct formula...