Phy P5 confusions (mine & your's).

[saifookhan]

Hi and Asalam o alaikum all.

I'm having some problems in Phy P5 questions.

-June 2008, Q2 part (d)
I am unable to find the units for 'η'. -PDF-

-Percentage uncertainty ones
Like: n09_52 & j10_52. Q2, last part for all.

Thanks for the help in advance.

Feel free to post your problems too in this thread.

 

[saifookhan]

Anyone?

 

[messi10]

Hi and Asalam o alaikum all.

I'm having some problems in Phy P5 questions.

-June 2008, Q2 part (d)
I am unable to find the units for 'η'. -PDF-

-Percentage uncertainty ones
Like: n09_52 & j10_52. Q2, last part for all.

Thanks for the help in advance.

Feel free to post your problems too in this thread.

June 2008:
Units of η are simple, look.
η = gradient/row
now go back and see the units of gradient, that are m^-1 (do not include s^-1 as you took log of it)

now put units in equation
η = m^-1/kg m^-3
so, units of η = kg^-1 m^2

Hope that helps

 

[talha-_-khan]

 

[messi10]

Nov 09 Q2, Last Part

Since you have found the b in above part. In my case that was 23.7 (so lets take this an example and continue last part)

For uncertainty in b, you have to do
1. Either Max value of b - min value of b and divide the answer by 2.
2. OR Max value of b - best value of b

I prefer the 2nd method as it saves time.

Since you have found the (e (i) ) answer 23.7 by using our g and t (that is given), its the best value.
Now find the max value, by taking max values of all variables in the same formula as in above part. So, it'll be like, t=(2.21+0.01) and g=(your answer of g in part d + your uncertainty value in part d)
put it in formula and calculate,
Now, you have max value of b, in my case its 26.4

Now take the difference, 26.4-23.7 = 2.7

For percentage uncertainty,
(2.4/23.7)*100 (23.7 because you have to take the original value i.e best value)
11.4%
That's the answer.

 

[messi10]

Can you please help me in Q1 diagram and little briefing ..
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_53.pdf

regards

 

[talha-_-khan]

Can you please help me in Q1 diagram and little briefing ..
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_53.pdf

regards

Examiner report and MS

 

[saifookhan]

Nice work bro. Thanks.
Just to mention you did a mistake there. It's not 30, it's 10.
Must have been a typo. You used 10 below which is right.

 

[saifookhan]

June 2008:
Units of η are simple, look.
η = gradient/row
now go back and see the units of gradient, that are m^-1 (do not include s^-1 as you took log of it)

now put units in equation
η = m^-1/kg m^-3
so, units of η = kg^-1 m^2

Hope that helps

Can you please elaborate the 's' part?

 

[saifookhan]

Nov 09 Q2, Last Part

Since you have found the b in above part. In my case that was 23.7 (so lets take this an example and continue last part)

For uncertainty in b, you have to do
1. Either Max value of b - min value of b and divide the answer by 2.
2. OR Max value of b - best value of b

I prefer the 2nd method as it saves time.

Since you have found the (e (i) ) answer 23.7 by using our g and t (that is given), its the best value.
Now find the max value, by taking max values of all variables in the same formula as in above part. So, it'll be like, t=(2.21+0.01) and g=(your answer of g in part d + your uncertainty value in part d)
put it in formula and calculate,
Now, you have max value of b, in my case its 26.4

Now take the difference, 26.4-23.7 = 2.7

For percentage uncertainty,
(2.4/23.7)*100 (23.7 because you have to take the original value i.e best value)
11.4%
That's the answer.

Thanks man. Totally understood your working.
Now the thing is, won't i get confused whether when to use this method and when not to? :s

 

[messi10]

Can you please elaborate the 's' part?

s part?
We are not taking units of s^-1 as we took log of it.

@your 2nd post.

You can use any, just remember, that if you do max-min then you have to divide by 2. If you do max-best, then don't divide by 2.
That's it.

 

[Ashrith]

Can someone help me with the diagram for Q1 in May/June 2008? :/
http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s08_qp_5.pdf

 

[talha-_-khan]

Nice work bro. Thanks.
Just to mention you did a mistake there. It's not 30, it's 10.
Must have been a typo. You used 10 below which is right.

yeah i did not notice it thanks for correction was typing mistake

 

[saifookhan]

M

Can someone help me with the diagram for Q1 in May/June 2008? :/
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_5.pdf

Man a similarquestion is repeated in N10_53.

 

[FRENZYAMU]

M
Man a similarquestion is repeated in N10_53.

u have to cover the whole surface of cross section of plate....written in ms, use a putty or metal plates for this

 

[saifookhan]

u have to cover the whole surface of cross section of plate....written in ms, use a putty or metal plates for this

Ah, yes! You're right. I forgot to add that point. :s

 

[Ashrith]

How do we find the absolute error if the value is squared. For example, A=2.1±0.1, how do we find A^2 along with the absolute error?

And could you also tell me how to calculate absolute error in a general form? :/

Thanks in advance!

 

[faangelica]

if log is taken for a value ,does its units cancel out?and dont we use the units in further calculations?

 

[faangelica]

How do we find the absolute error if the value is squared. For example, A=2.1±0.1, how do we find A^2 along with the absolute error?

(2.1+0.1)^2 - (2.1)^2

 

[saifookhan]

(2.1+0.1)^2 - (2.1)^2

We could also use
Δa^2 = 2Δa * a
but for this, we had to derive it..