From francis.Bryden at stcuthberts.school.nz Sun May 2 13:18:45 2010 From: francis.Bryden at stcuthberts.school.nz (Bryden, Francis) Date: Mon, 3 May 2010 08:18:45 +1200 Subject: year 12 Physics Course Message-ID: <6AC36C5F0F8E364CBEC8178DD499F3EF0120D164B3E1@stcc-exchange.stcuthberts.local> We are running a one day course for physics teachers ar St Cuthberts College. You or a colleague might be interested. It is designed for newish teachers or teachers without a physics background, but anyone is welcome We will look at: - Common misconceptions and how to deal with them - Experiments and demonstrations - How to use equipment - How to use Dataloggers - How to use Powerpoint and computer simulations This workshop is limited to 24 places For details, go to http://www.stcuthberts.school.nz/collegiatecentre/physics.aspx Thanks, ........ Francis Bryden Francis Bryden HoD Physics St Cuthbert's College 122 Market Rd Epsom 1021 PO Box 26 020 ph 64 09 520 4159 x 7808 ________________________________ Please consider the environment before printing this email -------------------------------------------------------------------------------- This message (and any associated files) is intended only for the use of the individual or entity to which it is addressed and may contain information that is confidential, subject to copyright or constitutes a trade secret. If you are not the intended recipient you are hereby notified that any dissemination, copying or distribution of this message, or files associated with this message, is strictly prohibited. If you have received this message in error, please notify us immediately by replying to the message or contacting helpdesk at stcuthberts.school.nz, and deleting it from your computer. Messages sent to and from us may be monitored. -------------- next part -------------- An HTML attachment was scrubbed... URL: From andydyson at actrix.co.nz Mon May 24 19:36:18 2010 From: andydyson at actrix.co.nz (andydyson at actrix.co.nz) Date: Tue, 25 May 2010 14:36:18 +1200 (NZST) Subject: exemplars Message-ID: Just been reading the exemplars for internally assessed AS on the NZQA website. http://www.nzqa.govt.nz/ncea/resources/physics/exemplars.html They have really clarified a number of points for me just as we are coming into our major assessment time. A great resource that I recommend everyone reads. One tiny point I saw which I'm unsure of though was in the level 2 measurement Student # 5 Grade: Merit / Excellence Thickness of 10 pages = 2 mm. Therefore thickness of 1 page = 0.20 mm. Appropriate use of significant figures. I thought that dividing by 10 did not change the number of sf but just increased the number of dp. Answer 0.2mm, same sf, extra dp. What do the rest of you teach? Andy Dyson, HoD Physics, Kerikeri High School in the relatively dry winterless Far North. From andydyson at actrix.co.nz Tue May 25 01:38:57 2010 From: andydyson at actrix.co.nz (andydyson at actrix.co.nz) Date: Tue, 25 May 2010 20:38:57 +1200 (NZST) Subject: exemplars Message-ID: <7c95eac4a9e865c104e211d93ebd3c11.squirrel@my.actrix.co.nz> Hi all, I posted a comment earlier today concerning sf and received several replies to me personally rather than to the list. I guess if one just clicks on reply with this list the reply only goes to the person doing the posting rather than the whole list. I'm sure that Marilyn and Fenella won't mind my copying their comments to the list to inform others: Since the sf is an indicator of the accuracy of the instrument I don't think the sf can be increased by mere mathematical processing - it is wholly dependent upon the smallest increment in the actual measuring device. That's my take on it. Fenella, Manurewa High School Totally agree with you (& not the exemplar) Marilyn Carter Diocesan School for Girls Thank you. I will stick to my original practice. Andy From robcampbell at actrix.co.nz Tue May 25 03:26:15 2010 From: robcampbell at actrix.co.nz (Rob Campbell) Date: Tue, 25 May 2010 22:26:15 +1200 Subject: exemplars In-Reply-To: References: Message-ID: The NZQA have it right this time. Suppose you had a list of numbers (like measured thicknesses of single sheets of paper.) You add them up and take the mean, which happens to be 0.2 mm. Should that be 0.20, 0.200, or maybe 0.2 ? You don't know unless you have the standard deviation. In Y13, we assume that devices like callipers can be read to +- one scale division, which looks as if it must be 0.1 mm here. Not +- .05 since you have to subtract the zero uncertainty. Okay. So the mean thickness value is 0.2 and the s.d. of single readings is 0.1 (sort of.) Stacking the sheets into a pile is a painless way of averaging thickness. It also means you're working with a sample of bits of paper, not individual sheets. And the s.d. of the sheets arrived at from measuring a sample is: s SD = ------- Sqrt(n) S = s.d. of sheets measured on their own SD = s.d. of sheets deduced from the sample measurement n = # of sheets in the sample: 10 sqrt (10) = 3.2 (Sorry about the crappy maths presentation.) The precision of that measurement from a sample is about three times that from measuring a single sheet. And the gain in accuracy is real. It's your prize for adopting an improved measuring technique. Cheers, Rob Campbell -----Original Message----- From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of andydyson at actrix.co.nz Sent: Tuesday, 25 May 2010 2:36 p.m. To: Phys-teach-talk at nzip.org.nz Subject: exemplars Just been reading the exemplars for internally assessed AS on the NZQA website. http://www.nzqa.govt.nz/ncea/resources/physics/exemplars.html They have really clarified a number of points for me just as we are coming into our major assessment time. A great resource that I recommend everyone reads. One tiny point I saw which I'm unsure of though was in the level 2 measurement Student # 5 Grade: Merit / Excellence Thickness of 10 pages = 2 mm. Therefore thickness of 1 page = 0.20 mm. Appropriate use of significant figures. I thought that dividing by 10 did not change the number of sf but just increased the number of dp. Answer 0.2mm, same sf, extra dp. What do the rest of you teach? Andy Dyson, HoD Physics, Kerikeri High School in the relatively dry winterless Far North. _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz From Terry.Moffat at rongotai.school.nz Tue May 25 14:27:41 2010 From: Terry.Moffat at rongotai.school.nz (Terry Moffat) Date: Wed, 26 May 2010 09:27:41 +1200 Subject: exemplars In-Reply-To: <7c95eac4a9e865c104e211d93ebd3c11.squirrel@my.actrix.co.nz> References: <7c95eac4a9e865c104e211d93ebd3c11.squirrel@my.actrix.co.nz> Message-ID: <4BFCE98E020000080000FF8B@smtp.rongotai.school.nz> Hi, I would have thought that to measure thickness they should be using a micrometer, and the reading initially should have been 2.00 mm. To use anything else would be unusual in that situation. I suspect we have a typo in the exemplar. Ta Terry >>> 25/05/2010 8:38 p.m. >>> Hi all, I posted a comment earlier today concerning sf and received several replies to me personally rather than to the list. I guess if one just clicks on reply with this list the reply only goes to the person doing the posting rather than the whole list. I'm sure that Marilyn and Fenella won't mind my copying their comments to the list to inform others: Since the sf is an indicator of the accuracy of the instrument I don't think the sf can be increased by mere mathematical processing - it is wholly dependent upon the smallest increment in the actual measuring device. That's my take on it. Fenella, Manurewa High School Totally agree with you (& not the exemplar) Marilyn Carter Diocesan School for Girls Thank you. I will stick to my original practice. Andy _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz -------------- next part -------------- An HTML attachment was scrubbed... URL: From suresh_chandra at xtra.co.nz Tue May 25 17:42:40 2010 From: suresh_chandra at xtra.co.nz (Suresh Chandra) Date: Tue, 25 May 2010 17:42:40 -0700 (PDT) Subject: exemplars In-Reply-To: <4BFCE98E020000080000FF8B@smtp.rongotai.school.nz> References: <7c95eac4a9e865c104e211d93ebd3c11.squirrel@my.actrix.co.nz> <4BFCE98E020000080000FF8B@smtp.rongotai.school.nz> Message-ID: <49451.84957.qm@web96002.mail.aue.yahoo.com> Hi , Could some one on the list help me - I can't access the document from the link given by Andy. I asked our IT administrator and his reply was there is no document linked to the link. He has promised to approach NZQA. Thanks in advance Suresh Chandra s.chandra at liston.school.nz ________________________________ From: Terry Moffat To: andydyson at actrix.co.nz; Phys-teach-talk at nzip.org.nz Sent: Wed, 26 May, 2010 9:27:41 AM Subject: Re: exemplars Hi, I would have thought that to measure thickness they should be using a micrometer, and the reading initially should have been 2.00 mm.. To use anything else would be unusual in that situation. I suspect we have a typo in the exemplar. Ta? Terry >>> 25/05/2010 8:38 p.m. >>> Hi all, I posted a comment earlier today concerning sf and received several replies to me personally rather than to the list. I guess if one just clicks on reply with this list the reply only goes to the person doing the posting rather than the whole list. I'm sure that Marilyn and Fenella won't mind my copying their comments to the list to inform others: Since the sf is an indicator of the accuracy of the instrument I don't think the sf can be increased by mere mathematical processing - it is wholly dependent upon the smallest increment in the actual measuring device.? That's my take on it. Fenella, Manurewa High School Totally agree with you (& not the exemplar) Marilyn Carter Diocesan School for Girls Thank you. I will stick to my original practice. Andy _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip..org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz -------------- next part -------------- An HTML attachment was scrubbed... URL: From whakamoe at clear.net.nz Fri May 28 13:00:04 2010 From: whakamoe at clear.net.nz (John Whakamoe) Date: Sat, 29 May 2010 08:00:04 +1200 Subject: re sf and rounding Message-ID: <94ABC536-C41D-4CD3-BC63-8CA9697C4943@clear.net.nz> HI All Here are a few ideas from me and below a few ideas from a colleague of mine, Derek Christie. I hope they help There is no doubt that by taking a ?larger? sample you do decrease the spread or variance of your estimate of the value being measured. I would note however that you are not taking a sample of 10 by taking the value of 10 each individual sheets, but a total of 10 sheets finding the variance of this set of ten and then dividing by the sample size 10. It still gives the same results s SD = ------- Sqrt(n) s = s.d. of sheets measured on their own SD = s.d. of sheets deduced from the sample measurement n = # of sheets in the sample: 10 ie you have reduced the sd of ?the total width of ten sheets divided10? by a factor of sqr(10) or about 3 ie the sd of our estimate for the value has been reduced by a factor of 3 The estimate of the value is now 0.2mm and if the sd of each individual sheet was (?sort of? see below**) +_ 0.01mm then this has now been reduced to 0.2 +_ 1/3x0.1mm or .03mm. Thus our estimated value is 0.20mm with a sd of +-0.03mm. However should we increase the number of sfs? **In fact this is a major problem. Somehow there has to be an estimate of the sd of each sheet and to measure this would require the use of an instrument. The reason why we used this method in the first place (take 10, find average, divide by 10) is because we cannot use our instrument to measure this. Ie the problem is the instrument more than the sd What happens if we go to the extreme? If we keep on increasing the sample size then the ?accuracy? (sd) will improve so 0.2 could become 0.20000mm based on the argument given (increasing the sample size). For instance: if we went to the ultimate extreme and did a census, in our case ?an infinite sample size?, then we know the value exactly (no variation). Based on the argument given, the value would be 0.20000000000?..mm Obviously not! The limit will be set by the limit of the measuring instrument, which brings us back to what is acceptable as the number of sf. Another way of saying this is to say the Normal Curve is getting ?thinner and thinner? as we increase the sample size and is coming closer to being a ?delta function? shape , or a vertical line. Before that is reached the width (sd) of the Normal Curve will be the same as the SD of the measuring instrument. After this, reducing the SD (increasing sample size) will not be the important factor in determining the number of sf but the measuring instrument will be. So the answer seems to be (at level 3 physics) not to get too wound up about it and accept both as you cannot tell with out more information (data) John Whakamoe From Derek Christie The question probably isn't well enough defined to have a single answer so your final comments are very likely right, but my sympathies are would lie with the teachers who say 0.2 at this level. I think the standard error versions are irrelevant here because the variance in paper thickness will be very small compared with the apparent instrument accuracy. The standard error gives the accuracy of the estimate of the average thickness of all sheets given a sample of true values. We are concerned about "the" thickness of a sheet assuming they are all the same. So we are really talking about the how the "divide by 10" part of our calculation affects the accuracy. What does "10 sheets = 2 mm" actually mean in this example? Unless you ask the kid "2.what?", it probably means that s/he is measuring to the nearest mm. Then 10 sheets are between 1.5 and 2.5 mm (ignoring the zeroing issue) so 1 sheet is between 0.15 and 0.25 so we say 0.2 mm. (I always taught 1/5 of a division, so perhaps this ruler has 1 cm divisions.) On the other hand, if they measure 100 sheets = 20 mm to 1 mm accuracy, then the answer would be 0.20 but then I suppose that we are dealing with 2sf even if it isn't so obvious. I would give the s/root(n) stuff a miss, myself, ingenious as it is. My view - the exemplar has it wrong. They should give a clearer, better thought out example. Cheers Derek -------------- next part -------------- An HTML attachment was scrubbed... URL: