You are Here: Home >< Physics

# Weird CIE A Level Physics 9702 rounding system watch

1. The thing is that I’m always practicing with past papers, and whenever I mark the answers, I get the s.f wrong. I don’t know wether they penalise you for it. I’ve been told that I should use the the smallest s.f given in the question, and that’s what I’ve been doing, but despite that, I’m still getting them wrong.

E.g: I just did a past paper and the question was an easy one: The Vrms of an AC source is 6.0 Volts, calculate its maximum value. I multiplied 6*sqrt(2) and gave me 8.4853 and I rounded it to 8.5 (cause the Voltage is given in 2 s.f hence using 2 s.f for the answer). But it seems that the answer is 8.48 !!!!!!!!!! And this led me to score zero on the following parts of the question cause they were based on it.

Can someone please explain me how it works. I’ve got many more examples, that’s just the latest one I did.

2. In my experience 3 sf is the safest bet in a theory paper unless the Q tells you otherwise.

It's when you do the practical one you have to be more alert to the sf in the data you're using.

Edited to add: It's pretty easy to justify giving the answer to 1 more sig fig than the question anyway. If you stick rigidly to the 'smallest sf given' rule then 3/2 would be 2, rather than 1.5.
Even in the practical part where you're completing data tables etc the m/s often gives eg 'to 3 or 4 sf' ie, giving you a choice between the 'smallest sf given' and one more.
3. (Original post by Iouass)
The thing is that I’m always practicing with past papers, and whenever I mark the answers, I get the s.f wrong. I don’t know wether they penalise you for it. I’ve been told that I should use the the smallest s.f given in the question, and that’s what I’ve been doing, but despite that, I’m still getting them wrong.

E.g: I just did a past paper and the question was an easy one: The Vrms of an AC source is 6.0 Volts, calculate its maximum value. I multiplied 6*sqrt(2) and gave me 8.4853 and I rounded it to 8.5 (cause the Voltage is given in 2 s.f hence using 2 s.f for the answer). But it seems that the answer is 8.48 !!!!!!!!!! And this led me to score zero on the following parts of the question cause they were based on it.

Can someone please explain me how it works. I’ve got many more examples, that’s just the latest one I did.

(Original post by Iouass)
....
E.g: I just did a past paper and the question was an easy one: The Vrms of an AC source is 6.0 Volts, calculate its maximum value. I multiplied 6*sqrt(2) and gave me 8.4853 and I rounded it to 8.5 (cause the Voltage is given in 2 s.f hence using 2 s.f for the answer). But it seems that the answer is 8.48 !!!!!!!!!! And this led me to score zero on the following parts of the question cause they were based on it.
Based on what you had done or written, you would not score zero but a full mark. Note that 8.48 is not a rounded up number.

I extract a portion of an Examiner Report to show how CIE deals with SF:
"...It is expected that the number of significant figures in calculated quantities should be the same or one more than the number of significant figures in the raw data...."

Whenever you use MS, do not blindly follow it. Read the cover page of the MS which says:

This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began.

All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 1, 2018
The home of Results and Clearing

### 2,869

people online now

### 1,567,000

students helped last year
Today on TSR

### Got into uni yesterday?

Come start a Freshers blog and win pizza!

### University open days

1. London Metropolitan University
Sat, 18 Aug '18
2. Edge Hill University
Sat, 18 Aug '18
3. Bournemouth University