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Physics Prac Sig Figs

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$!$RatJumper$!$:
Guys in paper 3 for the practical, i've been getting confised as in the number of sig figs/decimal places to put my answers.

What are the number of sig figs/decimal places for the following:

Metre Ruler
Time
Time Period
Ammeter
Voltmeter
Ohm Meter
Micrometer Screw Gauge
Vernier Calliper
Mass

Also, what are the uncertainty values for these?

Thankx

Deadly_king:

--- Quote from: $!$RatJumper$!$ on October 29, 2010, 06:06:00 am ---Guys in paper 3 for the practical, i've been getting confused as in the number of sig figs/decimal places to put my answers.

What are the number of sig figs/decimal places for the following:

Metre Ruler
Time
Time Period
Ammeter
Voltmeter
Ohm Meter
Micrometer Screw Gauge
Vernier Calliper
Mass

Also, what are the uncertainty values for these?

Thankx

--- End quote ---

Hmm..........it usually depends on the experiment being performed. So I can't really give you exact values :-\

A metre rule can measure values to the nearest millimetre. Hence if your values are in metres, the uncertainty will be 0.001. However since you'll be reading two values  (initial and final) you must multiply the uncertainty by 2.
This is the case only if you took every precaution to measure the length precisely. But if you are estimating the height, then you should take uncertainty to be between 0.02 - 0.05.

Uncertainty of time will depend on the stopwatch used (digital or analogue). Nevertheless, you need to add your reaction time to the uncertainty. Hence we usually take the uncertainty to be 0.2s. Time period will be the same uncertainty used as time. ;)

All the electronic apparatus will depend on the accuracy of the apparatus. ( No of decimal places)

Vernier calliper has uncertainty of 0.01 while micrometer has uncertainty of 0.001.

Hope it helps :)

Chingoo:
You're mixing up physical quantities and measuring instruments. Uncertainty and Significant Figures are determined by the measuring instrument. And since the measuring instrument in question could have any value as a smallest division, so listing them is a futile effort. However, what you do need to remember is:

Significant Figures should be uniform for every reading, like if you measured V1 across a resistor as 0.45 V, you should continue the list with two significant figures unless otherwise stated. They should be preferably taken to three significant figures for quantities like distance, mass, temperature, etc and up to four significant figures for quantities like time (time is more prone to error due to human reaction time). Of course, if your measuring device cannot provide a higher number of significant figures than one or two, then stick to them.

I'm not too sure what you want to know about 'uncertainty' of instruments; that's not really anything. If you were referring to the absolute error, then that is the smallest division on a measuring device e.g. on a meter rule, if the smallest division is of 0.1 cm, then the absolute error is +/- 0.1 cm.

Deadly_king:

--- Quote from: Chingoo on October 29, 2010, 07:01:04 am ---You're mixing up physical quantities and measuring instruments. Uncertainty and Significant Figures are determined by the measuring instrument. And since the measuring instrument in question could have any value as a smallest division, so listing them is a futile effort. However, what you do need to remember is:

Significant Figures should be uniform for every reading, like if you measured V1 across a resistor as 0.45 V, you should continue the list with two significant figures unless otherwise stated. They should be preferably taken to three significant figures for quantities like distance, mass, temperature, etc and up to four significant figures for quantities like time (time is more prone to error due to human reaction time). Of course, if your measuring device cannot provide a higher number of significant figures than one or two, then stick to them.

I'm not too sure what you want to know about 'uncertainty' of instruments; that's not really anything. If you were referring to the absolute error, then that is the smallest division on a measuring device e.g. on a meter rule, if the smallest division is of 0.1 cm, then the absolute error is +/- 0.1 cm.

--- End quote ---

Ooh......I guess i've mixed it up as well.

But usually you need to give the values correct to the same d.p as the uncertainty of the instrument used, right?

I mean if uncertainty is 0.1cm, you should give your values to one decimal point for centimetres and 3 decimal points for metres.

So the number of significant figures may depend on the instrument used.

But you are right, as far as possible we should be taking it to 3sf.

Example : If V was measured to be 0.50V and Current = 2.0A, then the power calculated should be to the mimimum number of S.f or one better.
P = IV = (0.5 x 2.0) = 1.0W

Power is given to 2sf since both I and V was measured correct to 2sf.

$!$RatJumper$!$:

--- Quote from: Deadly_king on October 29, 2010, 06:46:34 am ---Hmm..........it usually depends on the experiment being performed. So I can't really give you exact values :-\

A metre rule can measure values to the nearest millimetre. Hence if your values are in metres, the uncertainty will be 0.001. However since you'll be reading two values  (initial and final) you must multiply the uncertainty by 2.
This is the case only if you took every precaution to measure the length precisely. But if you are estimating the height, then you should take uncertainty to be between 0.02 - 0.05.

Uncertainty of time will depend on the stopwatch used (digital or analogue). Nevertheless, you need to add your reaction time to the uncertainty. Hence we usually take the uncertainty to be 0.2s. Time period will be the same uncertainty used as time. ;)

All the electronic apparatus will depend on the accuracy of the apparatus. ( No of decimal places)

Vernier calliper has uncertainty of 0.01 while micrometer has uncertainty of 0.001.

Hope it helps :)

--- End quote ---

"But if you are estimating the height, then you should take uncertainty to be between 0.02 - 0.05."

Don't you mean 0.002 - 0.005?

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