PERCENTAGE UNCERTAINTY....help

Could someone please explain how to work out percentage uncertainties with example using a stopwatch vernier and micrometer. Much appreciated!

Reply 1

andrew.awad

Micrometer the uncertainty is usually about 0.01. %Uncertainty 0.01/your value times a hundred
Vernier is usually about 0.02 so %Uncertainty is 0.02/your value times a hundred
the uncertainty is the lowest value u can take, so in a ruler u can only read to +- 1mm so uncertainty of ruler will be +-1mm,so %uncertainty will be 1mm/your vaule(mm) times a hundred

Reply 2

sphixter

What about for rulers and set squares? What is the uncertainity for them? Is it 0.5? And for thermometers and newtonmeters?

Reply 3

jobo3

1

rulers is 1 mm, the uncertainty of anything is just the lowest thing it measures to.

Reply 4

NesQuiK.

13

If revising this for AS module next week, you don't ever get questions on uncertainty

Reply 5

dkdeath

10

i thought you always divided the least with two so for a ruler 1mm is the smallest so it should be 0.5 mm , vernier caliper 0.05 mm and micrometer 0.005 mm

could anybody verify if this is correct ?

Lamp resistance measured – 609 666 639 661 654 628( in ohms)
first find the average value – 643
hat is the smallest value – 609
what is the maximum value – 666
what is the full range of values – 57
the uncertainty is half the range – 29
so % uncertainty = (28.5/643 ) x 100% = 4.4 %

Reply 6

sphixter

dkdeath

could anybody verify if this is correct ?

Lamp resistance measured – 609 666 639 661 654 628( in ohms)
first find the average value – 643
hat is the smallest value – 609
what is the maximum value – 666
what is the full range of values – 57
the uncertainty is half the range – 29
so % uncertainty = (28.5/643 ) x 100% = 4.4 %

What is this?

Reply 7

andrew.awad

dkdeath

i thought you always divided the least with two so for a ruler 1mm is the smallest so it should be 0.5 mm , vernier caliper 0.05 mm and micrometer 0.005 mm

could anybody verify if this is correct ?

Uncertainty of micrometer is 0.01
uncertainty of vernier is 0.02

Reply 8

silver-rose

In response to the above poster,

it's not always correct.

The uncertainty depends heavily on your method of measurement. There's no "set rule" that says you have to divide by at least two.

For example, if you were timing something manually with a stopwatch, the uncertainty be a rough estimate of the human response lag in the timing, as well as the inaccuracy of the stopwatch.

For vernier calipers and micrometers, the uncertainties are usually listed on the device.

Hope that helps.

Reply 9

unikq

dkdeath

i thought you always divided the least with two so for a ruler 1mm is the smallest so it should be 0.5 mm , vernier caliper 0.05 mm and micrometer 0.005 mm

could anybody verify if this is correct ?

Lamp resistance measured – 609 666 639 661 654 628( in ohms)
first find the average value – 643
hat is the smallest value – 609
what is the maximum value – 666
what is the full range of values – 57
the uncertainty is half the range – 29
so % uncertainty = (28.5/643 ) x 100% = 4.4 %

i was taught it like this bar the halving, dunno where that came from. thanks for refreshing my memory though

Reply 10

FO12DY

13

Hate to drag up an old thread, but I stumbled across this and I'd like to point out the reason for the confusion, for benefit of any other stumblers.

With a standard ruler, as per above example, uncertainty may be +/- 0.5mm. So the uncertainty is 1mm. Same for micrometer, but both divided by 10.

As it's 0.5mm uncertain in either direction, the 'total', if you like is twice that. That's what everyone's on about halving/doubling. If you include a +/- symbol, then your uncertainty will appear to be half that of it without - although really it's exactly the same.