Significant figures? (1 Viewer)

[QZP]

I'm having trouble with significant figures. Take for example this Q:
"The power distributed as 500v on a set of transmission lines is 500kW, and the resistance of the lines is 1.0 ohm."

I've learnt that 500 can be both 1 and 3 sig figs. So in this question, would the lowest be 1 (5 x 10^2) or 2 (1.0) ?

 

[anomalousdecay]

Its at least 2, since 1.0 ohm is specified.

It could also possibly be 3 sig. fig. as you said.

So just say the minimum is 2 or 3 (both may be correct as the question does not discriminate appropriately which one).

In this situation, to be safe, just write down at the end of your answer:

(X sig. fig. as specified).

Even if you get the X wrong, the marker knows that you are a good student who actually bothered to look at this (probably 80% of the cohort does not even look at the significant figure requirement).

 

[Fizzy_Cyst]

500 is one sig fig.

500 followed by a decimal point (500.) is 3 sig fig.

I would expect an answer to one sig fig for that question

 

[QZP]

500 is one sig fig.

500 followed by a decimal point (500.) is 3 sig fig.

I would expect an answer to one sig fig for that question

Oh really, that's interesting. I've never seen anything specified such as "300. V"
I'm only concerned about this because I heard that if I leave my answer with the incorrect number of significant figures, I outright lose a mark?

 

[anomalousdecay]

They won't say 300. V

They would say 300.0 V

But in that case wouldn't it be 4 sig. fig. ?

 

[Fizzy_Cyst]

^^ Yep, that would be 4 sig. figs.

I highly doubt that you would ever see 500. anywhere, lols

 

[Fizzy_Cyst]

Oh really, that's interesting. I've never seen anything specified such as "300. V"
I'm only concerned about this because I heard that if I leave my answer with the incorrect number of significant figures, I outright lose a mark?

No, not true.

your teacher may take marks off you for incorrect sig figs, in the HSC they dont take marks off you, but if you are expecting to be a Band 6 student, correct sig figs is something they expect of a Band 6 student, so you should do it

 

[anomalousdecay]

No, not true.

your teacher may take marks off you for incorrect sig figs, in the HSC they dont take marks off you, but if you are expecting to be a Band 6 student, correct sig figs is something they expect of a Band 6 student, so you should do it

Yeah this.

A group of markers look at your paper as a whole and determine whether you are a Band 6 student or not by simply looking at your Physics skill set and how you have communicated them. Just like Fizzy said at the seminar, there are many outcomes on the basis of how you communicate your knowledge and apply it to different exam questions.

So if you make one or two mistakes on the significant figures, then you could be fine providing that you got all the significant figures in other questions correct as the marker understands you have achieved the part of that outcome.

 

[QZP]

Oh, I thought they just go robot mode and give marks for hitting the marking criteria. I.e. Expression etc. don't really matter?

 

[Fizzy_Cyst]

Oh, I thought they just go robot mode and give marks for hitting the marking criteria. I.e. Expression etc. don't really matter?

Yes, but marking criteria can also be subjective to a degree

'demonstrates coherence and logical progression'

'demonstrates thorough knowledge and understanding'

'cause and effect of at least one significant positive effect'

All of this is from one question from the 2011 HSC -- some marking criteria are black and white, whereas some is a bit subjective (particularly the higher-mark questions) and marked in a holistic fashion, rather than such an analytical fashion.

Not too sure what you mean by 'expression' not mattering?

 

[QZP]

Yes, but marking criteria can also be subjective to a degree

'demonstrates coherence and logical progression'

'demonstrates thorough knowledge and understanding'

'cause and effect of at least one significant positive effect'

All of this is from one question from the 2011 HSC -- some marking criteria are black and white, whereas some is a bit subjective (particularly the higher-mark questions) and marked in a holistic fashion, rather than such an analytical fashion.

Not too sure what you mean by 'expression' not mattering?

I get it now, thanks I thought the marking criteria was all black and white that's why (even longer responses).

 

[strawberrye]

I get it now, thanks I thought the marking criteria was all black and white that's why (even longer responses).

Whenever a response is expressed in written form, there is always some slight subjectivity in one's marking. However, through doing practice exams and getting feedback by getting a teacher, for example, to mark your responses you will be able to understand what markers are looking for and maximise your chance of earning the higher marks in the exam.

 

[Fizzy_Cyst]

I get it now, thanks I thought the marking criteria was all black and white that's why (even longer responses).

There would not be too much subjectivity though as the marking groups are constantly monitored, samples taken and checked etc..

As strawberrye says, if you get someone who knows what they are doing to mark your stuff and give feedback you will pick up pretty quickly what you need to do

 

[jyu]

In reporting the results of scientific investigations, all measurements are in decimal form, e.g. 2.03 x 10^8 km indicating the number of significant figures. If a value is known to be exact, then it is considered to have infinitely many significant figures, e.g. 20 candles. In a question very often a quantity is given without decimal, e.g. 9 V and another quantity with decimal, e.g. 10.3 ohms. 9 V should be taken as exact (unless the writer says otherwise) and has infinitely many sig. figs whilst the quantity 10.3 ohms has 3 sig. figs. The calculated current will .: has 3 sig. figs.

 

[someth1ng]

In reporting the results of scientific investigations, all measurements are in decimal form, e.g. 2.03 x 10^8 km indicating the number of significant figures. If a value is known to be exact, then it is considered to have infinitely many significant figures, e.g. 20 candles. In a question very often a quantity is given without decimal, e.g. 9 V and another quantity with decimal, e.g. 10.3 ohms. 9 V should be taken as exact (unless the writer says otherwise) and has infinitely many sig. figs whilst the quantity 10.3 ohms has 3 sig. figs. The calculated current will .: has 3 sig. figs.

Never thought of it that way, very interesting.