# Physics Uncertanties

Discussion in 'Off Topic [BG]' started by Microbass, Apr 20, 2006.

1. ### Microbass

Jan 21, 2002
Glasgow, Scotland
OK, some of you may read my previous thread about my assessment.
I am trying to find the resonance frequency of an RLC and finiding out how the circuits behaves and a series and a parallel operation.
I used a signal generator to produce frequencies, and an oscilloscope to note the voltage across the resister.

My report on the subject has to contain three types of uncertainties; calibration, reading and random.
I'm clueless as to which results get which uncertainty. I guess that I would use the random uncertainty on the V(r) results?

help...

2. ### Geoff St. GermaineCommercial User

Random uncertainty relates to fluctuations of the result when the experiment is repeated. Generally in a high school or first year university course you will have to take multiple measurements at a few values of your independent variable (the one you are controlling) to get this.

I'm not familiar with the calibration uncertainty, but most likely it is the instrument uncertainty, or at least related to it. In most cases an instrument is only accurate to +/- X% depending on how the instrument is being used. This information sometimes appears on the instrument itself or may be in the manual. If you are actually calibrating an instrument for the experiment then it would relate to the method used to calibrate it. In this case it would be related to the accuracy of the device used for calibration.

Reading error would be the error in actually making a reading. You could probably equate this to the instrument uncertainty in many cases where you are using a digital readout. If you are using a ruler or vernier or some other sort of analog device the error is generally take to be half of the smallest division.

I remember in a first year physics lab when a student took his experiment to the professor to be marked. The student hadn't included any uncertainty at all. The prof asked "Do you think you are god?" and handed the report back.

3. ### simpy1

Mar 31, 2005
New Zealand
Geoff has it bang on.

Though for reading error I think that includes human error, like parallax error etc?

Random uncertainties - you won't have to write anything in-depth on them. Just any differences between identical experiments that you can't attribute to anything, those are random uncertainties.

4. ### Geoff St. GermaineCommercial User

It could. It depend on the particular experiment.