Is my textbook wrong about absolute uncertainties?

  • Thread starter Thread starter heroslayer99
  • Start date Start date
  • Tags Tags
    Precision Textbook
AI Thread Summary
The discussion centers on the definitions and distinctions between precision, accuracy, uncertainty, and resolution in measurements. It highlights confusion regarding the textbook's use of "precision" as a quantifiable value, suggesting it may actually refer to resolution. The participant questions whether absolute uncertainty should be half the resolution or the resolution itself, particularly in the context of a telescope's measurements. There is also a debate about the classification of errors and the interpretation of measurement differences. Overall, the conversation emphasizes the need for clarity in the definitions and applications of these concepts in scientific contexts.
heroslayer99
Messages
33
Reaction score
6
Homework Statement
The Hipparcos space telescope used stellar parallax with a precision of 9.7 × 10–4 arcseconds to
determine the distance to stars. Estimate the maximum stellar distance in parsecs that could be measured using Hipparcos. Calculate the percentage uncertainty in the calculated value of the distance to Polaris A if the parallax angle is 7.5 × 10–3 arcseconds.
Relevant Equations
d = 1/p
First off, I will set out what I think I know so that any misconceptions of mine can be put right.
Definitions:
Precision: a quality denoting the closeness of agreement between (consistency, low variability of) measured values obtained by repeated measurements
Accuracy: A quality denoting the closeness of agreement between a measured value and the true value
Uncertainty: interval within which the true value can be expected to lie
Resolution: Smallest increment on the instrument
In the case of a single reading, the abs uncertainty is half the resolution of the instrument, in the case of a measurement (the difference between two readings) the abs uncertainty is twice that of a single reading (twice the uncertainty in 1 reading is clearly just the resolution). For digital devices, like a voltmeter, approximate the abs uncertainty as half the resolution (same as a single reading).
What confuses me greatly is that in my problem I am told that the "precision" of the telescope is 9.7 x 10^-4, but from what I already know, precision (at least at the level I am working at, and the level that the textbook is written for), cannot be quantified, so I do not know what that value means, most likely it is the resolution, and the author has made a mistake. I am also confused as to whether the abs uncertainty is the quoted "resolution" or half this value. Finally, if this is the resolution then clearly the stated value for the parallax angle would be a multiple of this, turns out it isn't.
Please help :(
 
Physics news on Phys.org
Why make things difficult (if with a little bit of effort they can be made bloody impossible :wink:) ?

What if the observed parallax is simply ##75 \ \times 10^{-4} \ \ \pm \ 9.7 \ \times 10^{-4}## ? Can you answer the question?

##\ ##
 
heroslayer99 said:
Accuracy: A quality denoting the closeness of agreement between a measured value and the true value
According to https://en.wikipedia.org/wiki/Accuracy_and_precision, ISO defines it that way but others limit it to systematic error, making it independent of precision.
Presumably, resolution errors would be categorised as systematic (though by deliberately adding random errors and taking multiple readings they can be converted to random errors and thereby reduced).
heroslayer99 said:
in the case of a measurement (the difference between two readings)
Why would you describe the difference between two readings a "measurement "?

But, yes, I agree with you, it is sloppy. If precision (random error) is the only issue then you can get greater overall accuracy by averaging multiple readings. I would interpret it as here intending uncertainty from whatever cause.
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Thread 'A bead-mass oscillatory system problem'
I can't figure out how to find the velocity of the particle at 37 degrees. Basically the bead moves with velocity towards right let's call it v1. The particle moves with some velocity v2. In frame of the bead, the particle is performing circular motion. So v of particle wrt bead would be perpendicular to the string. But how would I find the velocity of particle in ground frame? I tried using vectors to figure it out and the angle is coming out to be extremely long. One equation is by work...

Similar threads

Back
Top