Physics Prac Sig Figs

[$!$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]

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

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]

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.

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$!$]

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

"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?

[Deadly_king]

"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?

Nope..........i said it right!

You cannot estimate in millimetres.Our eyes are not powerful enough

 Estimates are between 2cm and 5cm.

[$!$RatJumper$!$]

That doesnt make sense to me :/ If you are taking your uncertainty to be 0.001 for a normal ruler reading, it makes sense that an estimation of height should make you add about 0.001 to your uncertainty making it 0.002.

If you look at oct/nov 09 31 question 2(b)(iii) you will see what i mean.

[Deadly_king]

That doesnt make sense to me :/ If you are taking your uncertainty to be 0.001 for a normal ruler reading, it makes sense that an estimation of height should make you add about 0.001 to your uncertainty making it 0.002.

If you look at oct/nov 09 31 question 2(b)(iii) you will see what i mean.

Let's say you drop a ping-pong ball from a height of 1m from ground and you're asked to measure the height the ball reaches after the first rebound.

It's obvious that you won't be able to measure the exact value since the ball will reach there and instantaneously drop. Hence you should be estimating the maximum height.
Believe me, you won't be able to read the maximum height in millimetres. That's why the uncertainty is taken as 2cm - 5cm.

I'll take a look at the paper and let you know my opinions asap

[$!$RatJumper$!$]

Ok what u say makes sense .. .but according to what i can make out of the question paper, it tells me otherwise. anyways it would be gr8 if you could check it out and let me know what you think.

[Deadly_king]

Ok what u say makes sense .. .but according to what i can make out of the question paper, it tells me otherwise. anyways it would be gr8 if you could check it out and let me know what you think.

Damn it!.......My bad

How could I be so silly.........5cm is way too long for uncertainty.

In fact for the question, uncertainty should be 5mm.

c)(iii) 0.005/d x 100

Am really sorry for the confusion dude. All the uncertainties for estimates are taken to be 5mm and not 5cm.

[$!$RatJumper$!$]

Haha no problem dude we all make mistakes.. so don't worry about it. its what this forum is for! Past papers are such a blessing Thanks again buddy!

[Deadly_king]

Haha no problem dude we all make mistakes.. so don't worry about it. its what this forum is for! Past papers are such a blessing Thanks again buddy!

Yeah......you are right.

It's better that we make mistakes here than in the exams

No problem

[$!$RatJumper$!$]

hey. back on this topic... umm how many sig figs do i use for a measurment from a metre rule? would it be 1.000 m or 1.00 m?

[Deadly_king]

hey. back on this topic... umm how many sig figs do i use for a measurment from a metre rule? would it be 1.000 m or 1.00 m?

You should measure values equal to the minimum length that you're able to measure with the rule.

A metre rule can measure values in mm, hence it would be 1.000m

[$!$RatJumper$!$]

awesum thank you and for time how many sig figs? and time period