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 Post subject: Birefringence queston in assignment quiz GemA??
PostPosted: Mon Nov 16, 2009 1:11 pm 
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Hi All,

It me again :D .....me and my questions!

i did an assignment quiz today at GemA... there are 4 quizes, all going towards 20% of your mark as coursework, so they are quite important.
As they are all done online, the computer sometimes miss marks you and marks you as wrong, even if you are right and your tutor then remarks it.
You might get asked what colour something is, and you might say 'canary yellow' when the computer only wanted 'yellow'. It recognised the answer as being only yellow!

Anyway,

I had a weird birefringence question wrong!! In that i am sure it is right!!! Can anyone tell me if my answer is right? wrong. The suspense is killing me!!
i had a diagram (for anyone with the new dip file notes -Page D6-29, pattern VII).
Its a diagram of a biaxial (-ve) anisotropic refractometer reading! of which both moving lines are obviously variable and are touching. They touch at beta!
So alpha is 1.668
beta is 1.698
Gamma is 1.707

The birefringence i got was 0.039!! And it was marked wrong??!!

Am i not getting something? i thought the birefringence was calculated from the DR extremes alpha and gamma? and then subtracted??

Thanks

pxx


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PostPosted: Mon Nov 16, 2009 2:23 pm 
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Am i not getting something? i thought the birefringence was calculated from the DR extremes alpha and gamma? and then subtracted??


they are... maybe 'the computer' wants you to attach the sign as well? So... -0.039 might gain you more points...


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PostPosted: Mon Nov 16, 2009 3:14 pm 
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Hi Tim,

You reassure me, thanks...i thought i was going crazy...they didn't ask for sign...so hopefuly it was just a computer error...
Lets hope :D

pxx


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Sun Jan 30, 2011 2:45 pm 
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Hi,

I had the same question and the same problem. Was it an error? Or was the sign required?

Thanks!


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Thu Feb 03, 2011 6:28 pm 
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I had the same issue. I got that question in my first attempt and was marked wrong for 0.039. Looking at the table of constants, the stone has to be sinhalite - which has a birefringence of 0.038.

In the second test I had diagram -Page D6-29, pattern IV (biaxial negative)
Its a diagram of a biaxial (-ve) anisotropic refractometer reading of which one line is constant, the other is variable and are not touching.
alpha is 1.621
beta is 1.633
gamma is 1.643

This gives me a birefringence of 0.022. Again looking at the table of constants in the notes, the stone is pretty certain to be a tourmaline. The upper-end of the birefringence given for tourmaline is 0.021.

Having been marked wrong on the first attempt with 0.039, and seeing that the birefringences were all 0.001 higher than those given in the table of constants, I tried 0.021 as the answer and... was marked wrong again.

I would be suprised if they expected the sign and didn't specifically ask for it...

The computer system does drive me nuts - one the question asking for an alternative type of microscope used in gemmology other than a standard stereo. First attempt I put 'horizontal immersion microscope' and was marked wrong. Then spent a good 10 minutes establishing that I wasn't going crazy and it did exist. Second attempt put 'horizontal immersion' and ta dah... marked correct. Eugh!


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Thu Feb 03, 2011 7:07 pm 
pandora wrote:
The computer system does drive me nuts - one the question asking for an alternative type of microscope used in gemmology other than a standard stereo. First attempt I put 'horizontal immersion microscope' and was marked wrong. Then spent a good 10 minutes establishing that I wasn't going crazy and it did exist. Second attempt put 'horizontal immersion' and ta dah... marked correct. Eugh!


Comiserations.

What do you suppose the computer would have thought if you had entered 'Raman'? Grading by computer of answers to questions framed so as to permit lateral thinking in the derivation of a correct if unexpected answer - or which can't allow for typological error or phraseological or semantical variation is simply a bad idea. The purpose of interrogation is to determine how much a student knows. A computer marking answers to such questions can't make a good job of doing this.

*If* economics require computer grading of answers, then the questions must be capable of a binary (Y/N) answer or a short sequence of such binary answers entered in the correct order. Failing the provision of such a system, one would be much better served by opting for the ' tick the box' multiple choice form of interrogation, which a computer is equally capable of marking correctly.

Wasting time guessing the precise form in which the computer may be programmed to accept an answer as correct is a form of roulette and a waste of students' time and money. Equally, it can do no good at all to the reputation for competence of the examining body and the organisation it serves.

Just my half-crown's worth at bedtime :lol:


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Fri Feb 04, 2011 3:54 pm 
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Inclined to agree. It's my only gripe about the FGA.

Personally I liked the old-style assignments better (I started the Foundation as ODL - then had a kid etc when I was about halfway through the notes and so re-started 2 years later doing the evening classes). Okay so they could take a whole weekend to do properly but it gave me a chance to really absorb the information I was learning and to use the information I knew from personal experience and reading round the subject.

The computer test asks only for what is in the notes and getting a good grade depends as much on understanding how the test works as actually knowing the answers.

It sounds stupid being annoyed by one wrong answer, but it's 5% on that test. When it comes to the final result every percent can count.

I was wondering if it's possible to get copies of the old Diploma notes as I rather liked the layout (probably shows my age...) and I would like to work through the end of chapter assignments on my own.


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Sat Feb 05, 2011 10:50 am 
pandora wrote:
Inclined to agree. It's my only gripe about the FGA.

The computer test asks only for what is in the notes and getting a good grade depends as much on understanding how the test works as actually knowing the answers.

It sounds stupid being annoyed by one wrong answer, but it's 5% on that test. When it comes to the final result every percent can count.


It doesn't sound in the least stupid to me. This simply should not happen. And because it does happen in the example you give, I'd bet a pound to a pinch of snuff that the system is riddled with similar examples where those who perhaps are not aware of - or have not thought through - the strict limitations that need to apply to the computerised assessment of answers to questions framed by humans. It's not that the questions are bad - but the limitations in the computer programming that prevent the error-free recognition of a correct answer delivered in any one of many forms.

It's not for me to incite anyone to riot but I'd also opine that the situation is unlikely to improve unless its inadequacies are pointed out by all who suffer from them.

You seem to pine after a return to an older system. General experience of life suggests that this is an unlikely outcome. The rivers of time and change tend to run in one direction only - ever forwards and onwards with scant regard for nostalgia. If inadequacies in the present system for student interrogation are to be reported with a request for change, such requests (it seems to me) are more likely to produce a positive outcome if they can be associated with thoughts as to how the current system can be improved to obtain more certain evaluation of answers returned by students.

'Tick the box' answers to multiple choice questions may be the best way to go forward. Done properly this is actually not the lip-curlingly 'soft-option' that some British authorities are still prepared to dismiss it as. However, to be rigourous, it imposes greater demands on the skills and professionalism of those setting the questions :lol: It's worth remembering that (AFAIK) testing for IQ has always been mainly by 'multiple choice' interrogation - even in the UK :wink:


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Sat Feb 05, 2011 8:55 pm 
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I'm not generally known for being a wall-flower so I will be raising this as I already know that I am not the only person annoyed by it.

You're totally right about chances of return to the older system. I totally understand why the changes were made and the need to move with the times. I suppose it's like moaning about how much harder O levels were than GCSE's... probably were but won't change much.

My wanting the old notes is more for my own personal learning. Learning what you need to get x on an exam paper is one thing, leaning what you can about a subject is another. While I think the old assignments were better for absorbing the information I can see that they must have been a nightmare to mark for tutors with a large number of students - and they aren't family/work friendly! I'm happy to go with the new system as long as we're not losing marks because of computer glitches!

A lot of questions on the online assignments are multiple choice or arrange these answers with the correct question types. Then there are the one or two word answers and this is generally where the problems lie.


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 Post subject: Re: Birefringence queston in assignment quiz GemA??
PostPosted: Thu Feb 17, 2011 8:38 am 
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Just to finish the thread...

The correct answer was 0.039... it was purely a computer error.


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