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# A2 Physics:- Help Ideal gases Paper 4

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1. A2 Physics:- Help Ideal gases Paper 4
November 2009 Paper 42 - Attached9702_w09_qp_42.pdf
Question 2 c ii)
Marking scheme says that this question was deleted for insufficient information in question. What is the missing information? because I solved it and was surpriesed to know that it was omitted.
Last edited by The_Aviator; 13-05-2012 at 10:37.
2. Re: A2 Physics:- Help Ideal gases Paper 4
You just reminded me that i have an A2 physics paper soon
3. Re: A2 Physics:- Help Ideal gases Paper 4
4. Re: A2 Physics:- Help Ideal gases Paper 4
U = Mass x Specific Heat Capacity x change in temperate.
or rather
E = mcΔø
You did not have the mass or specific heat capacity
Only U which = 30J.
5. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by JonathanM)
U = Mass x Specific Heat Capacity x change in temperate.
or rather
E = mcΔø
You did not have the mass or specific heat capacity
Only U which = 30J.
why cant we use U = Ek + Ep and Ep = 0
So U = 3/2 k T ?
6. Re: A2 Physics:- Help Ideal gases Paper 4
Because you already have the energy but you don't have the mass or specific heat capacity lol. You're finding change in temperate "Δø"
7. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by JonathanM)
Because you already have the energy but you don't have the mass or specific heat capacity lol. You're finding change in temperate "Δø"
Im sorry for using your time, but I mean Delta U = 3/2 k Delta T
30 Joules = 3/2 x (8.314 / 6.02x10^23 ) x Delta T? Why wont this work?
8. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by JonathanM)
U = Mass x Specific Heat Capacity x change in temperate.
or rather
E = mcΔø
You did not have the mass or specific heat capacity
Only U which = 30J.
I mean I cant understand why you used this formula?
Why cant we use U = Ek? or U = P x Delta V = n R x Delta T??
9. Re: A2 Physics:- Help Ideal gases Paper 4
In this case where no PE exists as inter-molecular bonds are ignored. U = (3/2)Nkt = M C delta T

(3/2)kt or 1.5pV/N or 1.5nRT/N is the kinetic energy for a single particle lol. U is the total KE of the whole system 0.5Nm(v^2)
For all processes energy is of ORDER kT. We have specific equations for U like U = 1.5pV or 1.5Nkt or 1.5nRt
Last edited by JonathanM; 13-05-2012 at 19:05.
10. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by JonathanM)
In this case where no PE exists as inter-molecular bonds are ignored. U = (3/2)Nkt = M C delta T

(3/2)kt or 1.5pV/N or 1.5nRT/N is the kinetic energy for a single particle lol. U is the total KE of the whole system 0.5Nm(v^2)
For all processes energy is of ORDER kT. We have specific equations for U like U = 1.5pV or 1.5Nkt or 1.5nRt
Sir, I am sorry bt may you provide a more detailed , simpler explanation?
I cant seem to understand why cant we use U = 3/2 R/Na x T
or P delta V = U = N x k x Delta T.
I am really confused as to which formula to use and why you used mc delta T.
11. Re: A2 Physics:- Help Ideal gases Paper 4
It's the only one that gives us a change in temperature in g494 .

12. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by JonathanM)
It's the only one that gives us a change in temperature in g494 .

I already finished preparing for tmrw's exam. but then i came across this

Work done calculated is 30 Joules by P x delta V!
Internal energy of ideal gas at constant T = work done!
So U = P x Delta V. We are agreed on this.

Questions/Confusion:-

calculating temperature change.
1 - Is it possible to use the formula U = total change in kinetic energy
so 30 joules = 3/2 x N x k x Delta T ? If no, why not?

2- Is it possible to use the formula
U = work done = P x Delta V = n x R x Delta T? If no , why not?

Why is there a difference between P Delta V = n R Detla T
and P Delta V = 3/2 n R Delta T
When I am just using Thermodynamic laws?

13. Re: A2 Physics:- Help Ideal gases Paper 4
Can someone please explain the formulas of percentage uncertainty to use in different situations for A2 physics paper 6. I have the paper 6 exam next monday .......so please reply fast!!!!!
14. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by deathb4dishonour)
Can someone please explain the formulas of percentage uncertainty to use in different situations for A2 physics paper 6. I have the paper 6 exam next monday .......so please reply fast!!!!!
we dont have a paper 6 for a2!
15. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by The_Aviator)
why cant we use U = Ek + Ep and Ep = 0
So U = 3/2 k T ?
You've missed out the number of atoms -> U = 3/2 nRT (n = no. moles, which you are given)

Yes, you can do it if you know this, but the reason the question is removed is that you don't know the heat capacity because you're not expected to know equipartition theory. (As in you're not expected to know the 3/2kT per particle factor) It won't be on the syllabus. You've been taught it as an extra.

You could use the ideal gas equation I reckon, if you assume that pressure remains constant (which you sort of have to do for the first part)
16. Re: A2 Physics:- Help Ideal gases Paper 4
The question is impossible because to calculate the work done by the gas expanding you need to know either its initial temperature or pressure. Neither is given.
Atmospheric pressure is given but is irrelevant.
17. Re: A2 Physics:- Help Ideal gases Paper 4
(Original post by Stonebridge)
The question is impossible because to calculate the work done by the gas expanding you need to know either its initial temperature or pressure. Neither is given.
Atmospheric pressure is given but is irrelevant.
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