Decimal Places (2 Viewers)

[someth1ng]

What's the decimal place rule in Physics? Is it simply two decimal places?

 

[Rixon]

with sciences i'm pretty sure you use significant figures

and rule of thumb is to use the least amount of information you're given

 

[iSplicer]

What's the decimal place rule in Physics? Is it simply two decimal places?

Nope, sig figs. Look at the question, find the quantity with the least amount of SF and round your answer to that number of SF.

 

[iSplicer]

with sciences i'm pretty sure you use significant figures

and rule of thumb is to use the least amount of information you're given

+1

 

[nightweaver066]

I've been taught that in Physics, it doesn't matter.

Or maybe that's just my teacher..

 

[iSplicer]

I've been taught that in Physics, it doesn't matter.

Or maybe that's just my teacher..

It's just your teacher.

 

[someth1ng]

I was told that it was 2 decimal places in Physics at my school - so it's the same as Chemistry?

 

[nightweaver066]

I was told that it was 2 decimal places in Physics at my school - so it's the same as Chemistry?

Chemistry, use the lowest number of significant figures used in the question.

 

[Peeik]

I thought for sciences its always as follows:

If you are adding or subtracting up two numbers together you take the lowest number of decimal places.
If you are multiplying or dividing two numbers to take the lowest number of sig figs.

This is strongly emphasised particularly when you do sciences at uni. They're are very nitpicky about these things.

 

[D94]

I thought for sciences its always as follows:

If you are adding or subtracting up two numbers together you take the lowest number of decimal places.
If you are multiplying or dividing two numbers to take the lowest number of sig figs.

This is strongly emphasised particularly when you do sciences at uni. They're are very nitpicky about these things.

When you add/subtract decimals, when you take the least decimal places, it's just the same as taking the least significant figures. (Is there a trivial case?)

 

[Peeik]

Consider 1.3567 which has 4d.p. and 5s.f. plus 0.6 which has 1d.p and 1s.f. When you add the two together you get 1.9567 but you must leave answer to one dp so it should be 2.0 which has 1dp and 2sf.

If you were to multiply the two numbers together u get 0.81402 which will be 0.8 because it needs to be a number with 1s.f.

So there is a difference in either case.

 

[Fizzy_Cyst]

Whilst you will never lose marks (In Physics) for incorrect number of sig figs, it is one of the things that 'judges' look for in a Band 6 student.

So, if you end up with a mark of 89, they will look through your paper, see if you fit the Band 6 criteria, one of the criteria being correct sig figs, if you fit criteria they will award you a 90, if you dont, you are an 89.

So, although it doesnt REALLY matter, it is important for the students aiming high to do it correctly!

 

[someth1ng]

Consider 1.3567 which has 4d.p. and 5s.f. plus 0.6 which has 1d.p and 1s.f. When you add the two together you get 1.9567 but you must leave answer to one dp so it should be 2.0 which has 1dp and 2sf.

If you were to multiply the two numbers together u get 0.81402 which will be 0.8 because it needs to be a number with 1s.f.

So there is a difference in either case.

Why is the first one left with 2sf and not 1sf?

 

[Rathaen]

Why is the first one left with 2sf and not 1sf?

That'll be because 2.0 is effectively stating that the digit in the first decimal place is 0. If you were to simply have 2, that could mean anywhere between 1.5 and 2.5, assuming rounding.

2.0 would imply a greater amount of accuracy which would mean that the actual number is somewhere around 1.95 and 2.05.

Remember that in sciences you have to deal with levels of uncertainty coming from your measurement devices. The uncertainty or absolute error in a measurement will be half of the smallest increment that the device can measure. If you take a ruler for example, the smallest increment that you can see is 1mm (usually). If you used it to determine that the length of a line was 50mm, you would mark down that the length measured was 50mm (which then implies to anyone else reading your results that the uncertainty is 0.5mm).

If you say, used a pair of calipers which have a higher accuracy (+/- 0.05mm) and you measured the line to be 50.0mm long, then you would record that, again implying that your uncertainty is +/- 0.05mm. If you were to put down 50mm someone else might assume that your measurement was less accurate than it actually was.

Of course, you can also explicitly state the uncertainties (ie. 50 +/- 0.05mm) but this is basically what significant figures are used for.