Errors in practice GRE test

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Errors in practice GRE test

Postby noospace » Tue Sep 29, 2009 2:01 am

http://www.princeton.edu/~jdpeters/docs/ETS_extra.pdf

I think the answer to Q2 should be 1/3, not 3. What do you think?

I also don't see why you can't choose A for Q30. The hyperfine interaction of a spin-1/2 nucleus with j = 3/2 gives 3 states

f = i + j,... |i - j| = 2, 1, 0

I don't see why choice B is any better.

blackcat007
Posts: 378
Joined: Wed Mar 26, 2008 9:14 am

Re: Errors in practice GRE test

Postby blackcat007 » Tue Sep 29, 2009 2:13 am

noospace wrote:http://www.princeton.edu/~jdpeters/docs/ETS_extra.pdf

I think the answer to Q2 should be 1/3, not 3. What do you think?

I also don't see why you can't choose A for Q30. The hyperfine interaction of a spin-1/2 nucleus with j = 3/2 gives 3 states

f = i + j,... |i - j| = 2, 1, 0

I don't see why choice B is any better.


for question 2
viewtopic.php?f=19&t=2618

physics_auth
Posts: 160
Joined: Sat Jul 18, 2009 7:24 pm

Re: Errors in practice GRE test

Postby physics_auth » Tue Sep 29, 2009 2:35 pm

blackcat007 wrote:
noospace wrote:http://www.princeton.edu/~jdpeters/docs/ETS_extra.pdf

I think the answer to Q2 should be 1/3, not 3. What do you think?

I also don't see why you can't choose A for Q30. The hyperfine interaction of a spin-1/2 nucleus with j = 3/2 gives 3 states

f = i + j,... |i - j| = 2, 1, 0

I don't see why choice B is any better.


Then you have never heard of nuclear hyperfine interaction. This question is pretty easy but it can easily confuse somebody who does not know the phenomenon.
Physics_auth

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Re: Errors in practice GRE test

Postby noospace » Tue Sep 29, 2009 7:10 pm

Hi physics_auth,

Okay so what am I missing?

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Re: Errors in practice GRE test

Postby noospace » Tue Sep 29, 2009 7:14 pm

blackcat007 wrote:
noospace wrote:http://www.princeton.edu/~jdpeters/docs/ETS_extra.pdf

I think the answer to Q2 should be 1/3, not 3. What do you think?

I also don't see why you can't choose A for Q30. The hyperfine interaction of a spin-1/2 nucleus with j = 3/2 gives 3 states

f = i + j,... |i - j| = 2, 1, 0

I don't see why choice B is any better.


for question 2
viewtopic.php?f=19&t=2618


Ahh, right. How could I miss that?

Thanks.

physics_auth
Posts: 160
Joined: Sat Jul 18, 2009 7:24 pm

Re: Errors in practice GRE test

Postby physics_auth » Tue Sep 29, 2009 7:36 pm

noospace wrote:
blackcat007 wrote:
noospace wrote:http://www.princeton.edu/~jdpeters/docs/ETS_extra.pdf

I think the answer to Q2 should be 1/3, not 3. What do you think?

I also don't see why you can't choose A for Q30. The hyperfine interaction of a spin-1/2 nucleus with j = 3/2 gives 3 states

f = i + j,... |i - j| = 2, 1, 0

I don't see why choice B is any better.


for question 2
viewtopic.php?f=19&t=2618


Ahh, right. How could I miss that?

Thanks.



To stimulate you to search and find which is the correct answer, see page 613 of "Introductory Nuclear physics" by Kenneth.S.Krane. There you will learn why (B) is correct.
Physics_auth

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Re: Errors in practice GRE test

Postby noospace » Tue Sep 29, 2009 9:08 pm

Okay thanks for your help. But I don't see why you're giving me a reference to point out an arithmetic error quite frankly.

physics_auth
Posts: 160
Joined: Sat Jul 18, 2009 7:24 pm

Re: Errors in practice GRE test

Postby physics_auth » Wed Sep 30, 2009 5:27 am

noospace wrote:Okay thanks for your help. But I don't see why you're giving me a reference to point out an arithmetic error quite frankly.


It is not an arithmetic error. I made the reference to this book to stimulate you to read carefully the phenomenon and then see clearly why (B) is correct. If the whole matter was an arithmetic error, I would have written the answer, since it is requires a few minutes and a few lines ... . Is that clear? If you read it from a source you will definitely understand what is going on and you will not get confused about this matter in case you see a relative question in the test. The source I mentioned is enough to give you a clear undestanding.
Physics_auth

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Re: Errors in practice GRE test

Postby noospace » Wed Sep 30, 2009 7:32 am

Hi physics_auth,

As far as I can tell, this is simply a matter of realizing that spin-1 and spin 3/2 is the only combination that gives three states, which as I said, is an arithmetic error on my part.

I really think you are making a big deal out of nothing.

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Re: Errors in practice GRE test

Postby noospace » Thu Oct 01, 2009 6:25 am

physics_auth

Can't you just use the fact that 3/2 + 1 is the only combination which gives 3 states?

physics_auth
Posts: 160
Joined: Sat Jul 18, 2009 7:24 pm

Re: Errors in practice GRE test

Postby physics_auth » Thu Oct 01, 2009 9:50 am

noospace wrote:physics_auth

Can't you just use the fact that 3/2 + 1 is the only combination which gives 3 states?


This is exactly what I am implying ... that from the combination alone you cannot be sure; there is some kind of convention in the experimental method as to which result of the combination to keep so as to be able to find the spin by the number of lines ... and this explains why I mentioned a source to look at. For example, in a situation of different spins ... the number of lines gives the atom's spin not the nucleus' one (see Krane if you don't mind).
Ok?

Physics_auth

noospace
Posts: 46
Joined: Fri Feb 22, 2008 9:14 pm

Re: Errors in practice GRE test

Postby noospace » Thu Oct 01, 2009 6:02 pm

Okay, I'll try and have a look today. The problem is I don't have that book handy. I still don't see why my combination of angular momenta method isn't sufficient though.

physics_auth
Posts: 160
Joined: Sat Jul 18, 2009 7:24 pm

Re: Errors in practice GRE test

Postby physics_auth » Thu Oct 01, 2009 6:30 pm

noospace wrote:Okay, I'll try and have a look today. The problem is I don't have that book handy. I still don't see why my combination of angular momenta method isn't sufficient though.


I will try to give a brief explanation if I have time, in this post ... because other members may be interested.




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