Chris Hamper, 28 April 2012
It won't affect the moderation but you may get a comment saying that not all the syllabus was covered. I always do options at the end of the course so tend not to do so many practicals. EM would be a good option if you did want to do practical work though. Go to the page

Physics Symbiosis, 27 April 2012
The psow should include labs covering the topics of Core, AHL and Options. If options are not included, does it affect the moderation? If one does electromagnetic waves there is so much scope to do labs. Go to the page

Chris Hamper, 26 April 2012
You are right it should be +ve the velocity of the plane - the relative velocity of the two frames of reference 100-20 =80. I'll correct it right away, thanks for spotting it. Go to the page

Stephen Duncan, 25 April 2012
Hi Chris - Is the Q5 answer the right way around? Should it be 80ms-1 relative to the car rather than -80? Go to the page

Chris Hamper, 27 March 2012
Hi Nicola; I can't find where you left your comment so I'll answer here. You don't need to pay for more subscriptions for your students. if you go to settings then student access you will see a password. If they log into the site with this password it gets them into the student site with access only to the pages that you allow them to get to. You open the pages by ticking them in the student access page, underneath the password. Hope you work out how to do it. Go to the page

Nicola Jenkins, 27 March 2012
How do we get the sudents to see the student pages? When we subscribed we only had the 5 teacher login's. Do the students need a separate student login account? Go to the page

Chris Hamper, 21 March 2012
Fixed Go to the page

Chris Hamper, 21 March 2012
Both fixed. Go to the page

MEHMET EMIN KALE, 21 March 2012
"Black Hole answers" link is broken. Go to the page

MEHMET EMIN KALE, 21 March 2012
"Pound Rebka answers" link is broken. Go to the page

MEHMET EMIN KALE, 21 March 2012
Answer link is broken for "length contraction answers". Go to the page

Chris Hamper, 18 March 2012
I give them a final deadline (it was today at 1800) and if they don't hand in by then they get zero in the relevant criteria. If they come on the sample I register them as atypical and ask for a replacement. Go to the page

Albert Fong, 18 March 2012
What do you do about students who don't hand in some of the reports? Go to the page

Albert Fong, 18 March 2012
I've been using turnitin.com (students submit to the website, there's a grading function by typing comments) along with G4IA. Perhaps your colleagues would switch to that to become paper free? I think there is a subscription fee though. Go to the page

Chris Hamper, 12 February 2012
Yeah that's where I got the idea. Problem with that one is they are all different frequencies which makes it more beautiful but rather complicated to explain. Go to the page

Albert Fong, 12 February 2012
This is very similar, I showed this to my classes and they always ask to see it again. http://youtu.be/yVkdfJ9PkRQ Go to the page

Chris Hamper, 12 February 2012
One acceptable way is to take 1/2(max - min). The error associated with measurement is often much smaller than the spread of data. If you have a lot of data then standard deviation is better but there is no point if you only have 4 of 5 repetitions. The max min method can give slightly exaggerated error bars but that's something to talk about in the evaluation. Go to the page

Patrick Reilly, 12 February 2012
Quick question... what's an acceptable way for students to deal with error due to averaging a set of results. Is it acceptable to calculate the average and then simply state the error associated with the measurement or is some propagation calculation required? Go to the page

Chris Hamper, 31 January 2012
Hi Albert; Then both are marked and the best score counts. Go to the page

Albert Fong, 31 January 2012
What happens if a student attempts more than one question required in Section B of paper 2? Thanks Go to the page

Chris Hamper, 06 December 2011
The battery is an escalator and the internal resistance a stair case. Going around a cct is like walking round a shopping centre. If you take a trip round and end up at the same place you must have come down the same as you went up. A cell with internal resistance is like an elevator with a stair case after it. Try solving the problem with two parallel cells of different EMF without internal resistance but considering two escalators of different height. You can't solve it without joining them with a short staircase. Go to the page

Chris Hamper, 06 December 2011
Will sort it today. Go to the page

Chris Hamper, 06 December 2011
I'll be doing these and all the other 2011 past papers over the Christmas holiday. Maybe get this one done this week. Go to the page

Albert Fong, 05 December 2011
Would you please expand on the escalator analogy with regards to internal resistance? Go to the page

Alex Michael Bonnici, 05 December 2011
When will you be posting the solutions to paper 3 of May 2011? Go to the page

Alex Michael Bonnici, 05 December 2011
For some reason the answer sheet for Exponential decay is missing can you kindly post it!!!! Go to the page

Chris Hamper, 25 November 2011
Oh no.:-( I'd ask for the probes to be replaced, they should be able to be put in boiling water I think. I have got through quite a few probes in my time but hadn't connected it to this experiment. I'll be doing this one next week with my class so I'll tell them not to heat the water over 50 degrees. Thanks for pointing out this potential problem. Go to the page

David Mulholland, 24 November 2011
Hi Chris, this is a great lab and my Grade 12 students got some good results, but all at the expense of 3 Vernier temp probes! I got them to just stick the probes down the spout of the kettle - is that what you do? Having spoken to Vernier they say steam may have passed inside the plastic handle/casing and damaged them, even though they have a safe working limit of 150C. Cheers, dave Go to the page

Chris Hamper, 31 October 2011
Oops! and fixed, thanks. Go to the page

Mary Orfila, 30 October 2011
On #2, in your solution, 0.001 should be 0.01 -- Thanks for the great resources! Go to the page

Chris Hamper, 26 October 2011
Yes, I think the easiest way is to make a mark for the length and vary the speed to make it balance. An alternative is to spin at a constant rate given by a metronome then pinch the string before it stops and measure the length. Some of my students insisted on doing it this way but I can't remember how successful they were. Go to the page

Albert Fong, 26 October 2011
Is there a smart way to measure the length? Or do we ask the students to mark off the lengths on the string and try to get it to the correct position by varying the spin speed? Go to the page

Chris Hamper, 11 October 2011
The HL solutions are here http://www.contentextra.com/bacconline/bacContentFiles/physicsFiles/PhysicsHLSolutions/index.html Sorry can't do links in comments. And the SL ones http://www.contentextra.com/bacconline/bacContentFiles/physicsFiles/PhysicsSLanswersfinal/index.html Go to the page

Keith Browne, 11 October 2011
Dear Chris. You mention a solutions website that for use with your book. Although we use the book I was unaware that this was available. Where would I find it? Thanks Go to the page

Chris Hamper, 10 October 2011
Yep, you're right at least you were because now it's fixed. One day I will go through and add all those comments. I remember that was one I added to see if it worked. Thanks for pointing it out. Go to the page

, 10 October 2011
Hi Chris, just a note that when in the Teaching Resources page and looking at the "2nd Law mc test", the comment on the right hand side of the page indicates Newton's 2nd Law, but the link is to the 2nd law of thermodynamics. Cheers, dave. Go to the page

Chris Hamper, 12 September 2011
It isn't. Forces are balanced so the centre of gravity doesn't move. Go to the page

Ian Ritchie, 10 September 2011
Q1 - you did not mention the object was fixed at centre. Go to the page

Chris Hamper, 05 September 2011
No need to quote the intercept unless you are going to use it. It is of course included in the equation and will be useful when it comes to the evaluation. Go to the page

Greg Groeschl, 03 September 2011
The gradient and what else should be quoted? the y-intercept? Go to the page

Chris Hamper, 01 September 2011
Yes, some times clicking show takes you to the home page. I have passed on the feedback to the site developer. Go to the page

Chris Hamper, 01 September 2011
Fixed. Thanks for spotting the mistake. Go to the page

Torbjörn Klaesson, 29 August 2011
Question 6 is really 6.0 given with ONE significant figure? Go to the page

Ian Ritchie, 29 August 2011
Nice questions and animations etc. Only problem is the answers will not "show"... or only about half of them do. Go to the page

Chris Hamper, 06 June 2011
I finished with marking a week ago. I like to get it all done and dusted before the holiday. When I see the massive pack of papers that my friend in the chemistry dept. has just sent back to Cardiff I feel very saintly. Go to the page

John McMurtry, 04 June 2011
I am getting used to the scoris system in Biology but it is much slower than the paper scripts. I certain do hope that the quality control aspect will hold true as everyone races to meet the deadlines. My neck gets really stiff with this emarking! Go to the page

John McMurtry, 11 May 2011
I really liked the melting chocolate bar to measure the speed of light! Go to the page

Geoffrey Neuss, 31 March 2011
Are you referring to his large brain or his intelligent expression - or perhaps both? Go to the page

Chris Hamper, 31 March 2011
I thought Avagadro was a physicist but to come to think of it he does look more like a chemist. Go to the page

Geoffrey Neuss, 30 March 2011
You should leave the chemistry to chemists Chris! Avogadro is famous for coming up with the idea of molecules (atoms are Dalton). Avogadro's work in 1811 was actually entitled "Essai d'une manière de déterminer les masses relatives des molécules élémentaires des corps, et les proportions selon lesquelles elles entrent dans ces combinaisons" so his idea was that equal volumes of gases at the same temperature and pressure contain the same number of molecules - not atoms! Even though it built upon the observations made by Gay-Lussac in 1809 no one really took Avogadro's work seriously until the work of another Italian chemist in 1858 - Stanislav Cannizzaro - showed its importance. Go to the page

Geoffrey Neuss, 20 March 2011
I'll come and watch you do it Chris. I think the final point about the mattress is the key. Pole vaulters land from a height of over six metres onto a mattress - and they usually land on their back! Go to the page

Geoffrey Neuss, 19 February 2011
I'd also like my pilots to have practiced on more than just a flight simulator. They also talk about a new name for the Group 4 subjects. In line with their 'blurring of the distinction....' maybe they will come up with 'The virtual sciences'! Go to the page

, 08 February 2011
Did it myself and got a reasonably straight line with a gradient of 700nm which is quite close to the 500nm they are supposed to be. Being colour blind I couldn't do all the colours though so only had 4 points on the graph. Go to the page

Chris Hamper, 08 February 2011
Hi Alex; I haven't done this with my class yet so don't have a student report. Might see if I can put one together myself though. Go to the page

Alex Michael Bonnici, 08 February 2011
Hello Chris, Do you have a full student report sample for the experiment Diffraction from a CD. I am thinking of doing this experiment with my first year HL students within the next 2 weeks. This a wonderful Lab. Best regards, Alex Go to the page

Alex Michael Bonnici, 02 February 2011
I found the advice here very informative!!! This is my first time writing a Supervisor’s Extended Essay Report and a bit apprehensive. Thanks for helping me over come my fears. Go to the page

, 30 November 2010
But why does it only appear on twigs and not stones or anything else? See the leaves in the background have only a bit of frost on them but the twig has loads. I don't think this is rime, we have lots of that here at the moment and this stuff is different, much more fragile and fibrous like asbestos. It tends to appear when its not that cold, sometimes the only frost around is coming out of twigs. I'll get some better photos. Go to the page

, 30 November 2010
The video should play on the page. Maybe it doesn't work in all browsers, I use firefox. Go to the page

Amy Brown, 29 November 2010
Very helpful, Chris. Discussion on our absolutes and how we justify such assertions is always a good one. The philosopy teacher has been a little icy since the class carried their discussion on doubt into physics... I couldn't see the link the the chemistry video - is that to come? Go to the page

Geoff Neuss, 27 November 2010
Chris, what you are observing is called hoar frost or more particularly rime. You also see it on fence posts when winter mountaineering in Scottish hills etc. The twig cools (by radiation) to a temperature below zero and if the air is supersaturated water droplets condense on the twig. Mist and fog droplets are smaller than rain droplets so the heat released as they crystallise (freeze) can be quickly conducted away so the whole droplet freezes rapidly. As more and more cold mist droplets hit the windward side of the object they build up a mass of porous ice (called rime). In winter mountaineering it is a way to see what the prevailing winds were and whether they have now changed direction which can give information on fronts passing over etc – I’ve told you before that climbing gives you a good education! Go to the page

physics, 02 November 2010
Well just incase you do come back, yes the students work in pairs then the one who had the idea does the report. I don't really have enough room in the lab for 18 different practicals. Go to the page

physics, 02 November 2010
Yeah images in comments would be nice I'll pass this on to the web designer. By the way the post now has an image that was supposed to be there but for some reason disappeared. I tried to take a photo of what they were looking out but it didn't come out well. Go to the page

fredi, 02 November 2010
These are really helpful for IB teachers. Go to the page

tonetappel, 02 November 2010
I want to post an image response! This is a post that needs an illustration, and if I could post my reply as a photo that would be nice. Is it possible to add that function within this framework and without typing html code? Or are you trying to avoid extensive maintenance work removing inappropriate material? (As you have to pay and register I would not think that would be a major problem.) Go to the page

tonetappel, 02 November 2010
So this means you do design in groups? And then just one of the students hand in reports? Or? (I realise I'd rather post this comment in the occ forum since I probably wouldn't come back to check this post and possible replies at a later stage...) Go to the page