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# 19/05/10 Edexcel Phy 6(6PH08) watch

1. (Original post by ishta)
Guyz how are youll calculating uncertainty if there is more than one value

for eg 24.1,25.3,25.6 cm (+/-0.01cm)

IS it half range ?

25.6-24.1 divided by 2 ??
yep. That's the way to calculate half range.

If the half range(HR) is greater than uncertainty, U(I), use half range and vice versa.

Then it is [U(I) or HR]/[avg value] x 100

Is the percentage uncertainty 3%? I got that value and I am not a natural at physics
2. Can anyone please teach me how to find uncertainity and percentage uncertainty when there are average values and sstuff

for example
Code:
```20T/s 20T/s Mean T/s
18.66 18.62 0.932```
3. (Original post by sarboom)
oh and btw they have a zip file with almost all the A level core practicals in freeexampapers

http://www.srepapmaxeeeerf.org/A%20L...Practicals.zip

hope it helps
Thanks!! xD
4. (Original post by antonfigo)
Can anyone please teach me how to find uncertainity and percentage uncertainty when there are average values and sstuff

for example
Code:
```20T/s 20T/s Mean T/s
18.66 18.62 0.932```
well, for this question, the uncertainity in reading the time is distributed throughout the 20 attempts, that's we use this equation!

absolute uncertainity/(0.932*20) * 100%
5. GUYS I'm freaking out!
anyone with any useful resources to be used tmrww????
6. (Original post by Bronze92)
well, for this question, the uncertainity in reading the time is distributed throughout the 20 attempts, that's we use this equation!

absolute uncertainity/(0.932*20) * 100%
Thanks! you are awesome and probably have earned me one mark.!

Code:
```(b) The engineer obtained three sets of data.  The values for the Young modulus were
14.2, 14.7 and 15.1 GPa.
Determine the average value and state its uncertainty.
(2)```
i am getting a wrong answer

found average which is 14.7

then did it 0.1/14.7 = wrong answer....
the rihgt answer is + or - 0.5
7. (Original post by antonfigo)
Can anyone please teach me how to find uncertainity and percentage uncertainty when there are average values and sstuff

for example
Code:
```20T/s 20T/s Mean T/s
18.66 18.62 0.932```
We actually carried out a lotta experiments in the school lab so my teacher says that if you time more than 1 oscillation the percentage error for the experiment is reduced as the percentage inaccuracy when you'd time just 1 oscillation would be very high. Take for example that the uncertainty for the stopwatch is 0.1s( i dunno what to say but the SAM mark scheme says its suppose to be 0.5s but i guess i'll stick with 0.1s as in almost every other mark scheme ive seen till now 0.1s is THE uncertainty) then the percentage uncertainty if you time just 1 oscillation would be (0.1/0.932)*100 which is improbably large! but if you time 20 oscillations then your percentage uncertainty is (0.1/mean of20T)*100 which is smaller

Also you could say that the uncertainty for the timer(ie. stopwatch) is 0.2s as 0.1*2=0.2s due to the time it takes for a human to START and STOP a timer ( yeah... this is where that human reaction time bullcrap kicks in )
8. (Original post by antonfigo)
Thanks! you are awesome and probably have earned me one mark.!

Code:
```(b) The engineer obtained three sets of data.  The values for the Young modulus were
14.2, 14.7 and 15.1 GPa.
Determine the average value and state its uncertainty.
(2)```
i am getting a wrong answer

found average which is 14.7

then did it 0.1/14.7 = wrong answer....
the rihgt answer is + or - 0.5
Ur average is correct then to find the uncertainty
its 0.5(Highest -lowest)
so ut l be 0.45 which rounds off to 0.5

Do you have more of these type of questions if you do can you please post them if will a great help
9. (Original post by sarboom)
We actually carried out a lotta experiments in the school lab so my teacher says that if you time more than 1 oscillation the percentage error for the experiment is reduced as the percentage inaccuracy when you'd time just 1 oscillation would be very high. Take for example that the uncertainty for the stopwatch is 0.1s( i dunno what to say but the SAM mark scheme says its suppose to be 0.5s but i guess i'll stick with 0.1s as in almost every other mark scheme ive seen till now 0.1s is THE uncertainty) then the percentage uncertainty if you time just 1 oscillation would be (0.1/0.932)*100 which is improbably large! but if you time 20 oscillations then your percentage uncertainty is (0.1/mean of20T)*100 which is smaller

Also you could say that the uncertainty for the timer(ie. stopwatch) is 0.2s as 0.1*2=0.2s due to the time it takes for a human to START and STOP a timer ( yeah... this is where that human reaction time bullcrap kicks in )

I thought about that too... in my notes also it says that human reaction time is 0.1 secs while a circuit (electronically triggered) timer has an uncertainty of 0.01 secs...

Bullcrap indeed..

also do i have to check thatt is the half range is smaller than uncertainty of the human reaction?
10. (Original post by antonfigo)
I thought about that too... in my notes also it says that human reaction time is 0.1 secs while a circuit (electronically triggered) timer has an uncertainty of 0.01 secs...

Bullcrap indeed..

also do i have to check thatt is the half range is smaller than uncertainty of the human reaction?

yep then you take the bigger one which is the reaction time in example in the SAM
11. (Original post by ishta)
Ur average is correct then to find the uncertainty
its 0.5(Highest -lowest)
so ut l be 0.45 which rounds off to 0.5

Do you have more of these type of questions if you do can you please post them if will a great help
these two questions are the only uncertainty questions i have found .... its from the SAM and the last january 3B paper....

And ... where does that 0.5 come from..... half range ?...i don't understand
12. (Original post by antonfigo)
these two questions are the only uncertainty questions i have found .... its from the SAM and the last january 3B paper....

And ... where does that 0.5 come from..... half range ?...i don't understand
yep half range!!! do U get it nw??
13. (Original post by ishta)
yep half range!!! do U get it nw??
yea i guess so thanks

also ... how would i know if the graph should or should not pass through origin....the poins may come really close!.....check question 3 of SAM...
14. well that would give 0.02s as the uncertainty here so i think that wont be right as you are definitely using a stopwatch for this experiment
15. Has anyone got any clear idea or suggestions about what will be there for the practical physics paper? has anyone finished the exam yet?
16. (Original post by youngmoney)
Has anyone got any clear idea or suggestions about what will be there for the practical physics paper? has anyone finished the exam yet?
this is the first unit 6B examination for the new spec so no oness actually ever sat for this exam before
17. (Original post by antonfigo)
yea i guess so thanks

also ... how would i know if the graph should or should not pass through origin....the poins may come really close!.....check question 3 of SAM...
Draw the graph, continue the line to the left, you'll see that it hits the y axis at something that is not zero. therefore, not the origin.
18. Guyz have youll got any uncertainty questions except from the SAM and the old 3Bs??
19. whats the meaning of qualitatively and quantitatively ?
20. (Original post by ishta)
Guyz have youll got any uncertainty questions except from the SAM and the old 3Bs??
the old 5Bs

and the Salter's Horners text book as some, I think..

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