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Fluid Prisms

1 min read

With cut backs and lower budgets, often the variety of equipment individual departments can afford is not ideal. With optics, for example, you can have numerous prisms and blocks of differing refractive index for the pupils to play with… but all have a cost. Here we look at a cheaper alternative to increasing the range of refractive indices which you would have at your disposal.


I made use of the refractive nature of sugar solution to make a series of prisms with petri dishes as the container. Data courtesy of Gustavus Adolphus College.

“screen” “screen”

Density and refractive indexes of sucrose

Density (g/cm^3) Refractive index % by weight (w/v) Molarity
0.9982 1.3330 0
1.0021 1.3344 1 0.029
1.0060 1.3359 2 0.059
1.0099 1.3374 3 0.089
1.0139 1.3388 4 0.119
1.0179 1.3403 5 0.149
1.0219 1.3418 6 0.179
1.0259 1.3433 7 0.210
1.0299 1.3488 8 0.211
1.0340 1.3464 9 0.272
1.0381 1.3479 10 0.303
1.0423 1.3494 11 0.335
1.0465 1.3510 12 0.367
1.0507 1.3526 13 0.399
1.0549 1.3541 14 0.431
1.0592 1.3557 15 0.464
1.0635 1.3573 16 0.497
1.0678 1.3590 17 0.530
1.0721 1.3606 18 0.564
1.0765 1.3622 19 0.597
1.0810 1.3639 20 0.632
1.0854 1.3655 21 0.666
1.0899 1.3672 22 0.701
1.0944 1.3689 23 0.735
1.0990 1.3706 24 0.771
1.1036 1.3723 25 0.806
1.1082 1.3740 26 0.842
1.1128 1.3758 27 0.878
1.1175 1.3775 28 0.914
1.1222 1.3793 29 0.951
1.1270 1.3811 30 0.988
1.1318 1.3829 31 1.025
1.1366 1.3847 32 1.063
1.1415 1.3865 33 1.100
1.1463 1.3883 34 1.138
1.1513 1.3902 35 1.177
1.1562 1.3920 36 1.216
1.1612 1.3939 37 1.255
1.1663 1.3958 38 1.295
1.1713 1.3978 39 1.334
1.1764 1.3997 40 1.375
1.1816 1.4016 41 1.415
1.1868 1.4036 42 1.456
1.1920 1.4056 43 1.498
1.1972 1.4076 44 1.539
1.2025 1.4096 45 1.581
1.2296 1.4200 50 1.796
1.2575 1.4307 55 2.020
1.2865 1.4418 60 2.255
1.3163 1.4532 65 2.500

Besides the usual refractive behaviour of light within the medium, it is also possible to demonstrate total internal reflection within the fluid itself.


Basically, what we have is cheap and easy way of having a variety of prisms with a number of refractive indices for the price of some sugar, water and a reusable petri-dish.

If you want any more info or have any ideas, you can [tweet me](

Making Navigable VRs

1 min read

In pursuit of novelty out-of-classroom teaching methods, Photosynth is a product from Microsoft research which allows you to stitch panoramas into immerse VRs - see below. ( or click here if all you see is a blank space).

The synth above is to be part of a lesson on the environmental impact of energy generation. A GoogleForm will host the questions related to the individual synth and will allow me to collate the pupil responses electronically. Although a glorified picture of the area, hopefully it will add a little novelty to the work.

There is a free and easy to use mobile app which allows you to directly make the synths on your iOS device or Windows phone (see screenshot below, but you can take higher resolution synths with a regular camera and stitch them together online.


If you want any more info or have any ideas, you can tweet me.


Make a Thermogram without an IR Camera

1 min read

Here we have a look at a SIGNIFICANTLY cheaper (but very low resolution) way to create thermograms.


When teaching heat transfer mechanisms to my GCSE class, I wanted to get the pupils to make their own thermograms and to learn about how these images are rendered. Using the setup above (with hot water), an IR thermometer and a couple of conditionally formatted spreadsheets, the pupils are able to create very low resolution thermograms.

Using the Infrared thermometer, the pupils take the temperature through each of the grid cells, the numerical data are input in to one spreadsheet:.


Conditional formatting in the workbook allows you to create a heat-map colour scale from the temperatures.


An additional teaching point here could be to show the differences in resolution by moving the grid different distances from the objects.

If you want any more info or have any ideas, you can tweet me.


A Taste of Research: Citizen Science

2 min read

Here we have possible enrichment activities for MAT pupils:

Humans are good at finding patterns in things which aren't there. That is the reason why this morning when I was cycling to work, I looked up and saw a dinosaur in the clouds above. Either that, or the Beecham's  I'm taking for my cold is stronger than I thought. This phenomenon is known as apophenia - the ability of humans to see patterns in seemingly random data. Programming a computer to perform the same task is difficult. For example, if you show a five year old a chair, they will know it's a chair. Show the same five year old the same chair but with no back and it is still recognised as a device for sitting. Repeat the experiment again with a computer in the place of the five year old. Objectively, there is no difference between a backless chair and a table, it is this distinction which makes the job of optical recognition difficult for the computer. 

The study of galaxy structure, or morphology, is one such appearance of this recognition problem. There are many different morphologies of galaxy, from ellipticals to spirals to lenticulars and irregulars, a vast array of shapes to be classified in the deepest of Hubble deep-field-surveys. Humans are significantly more adept at recognising patterns than some of the most powerful computers - unfortunately, a human's time is more expensive than CPU time. That being said, there is an opportunity for people with a taste for research to get involved in the large-scale project of classifying millions of galaxies. The GalaxyZOO project enables the general public to get involved in the classification of galaxies and to contribute to the every growing knowledge base. It gives members of the public an idea as to what it's like to be a research scientist (at least in astronomy!).

There are other citizen science projects run out of Zooniverse and perhaps you could direct your students to one of these. At the very least it is something for the UCAS statement, at the most it will cultivate an interest in doing real science outside the classroom.


Audio Feedback: Mobile

2 min read

Last week I blogged over on about providing marking for my students via an audio file which they listen to and address the comments I make. 

As I mentioned in the blog post, I tend to use Audacity on my computer to record and distribute the feedback through Google Drive. However, with the increasing ubiquity of smart phones and tablets, there are more teachers who have access to these mobile devices in school over computers. There are many different audio recording solutions on the various app stores, but the following two stand out for having dropbox/Google Drive functionality and various file format exports. I am in no way affiliated with any of these companies, but I thought a few suggestions would be useful.

iOS - Voice Record Pro, by Dayana Networks LTD.

The built in memo recorder in iOS can be a little temperamental, so this app has numerous export options in terms of destination and format. It is currently available on the UK and US iTunes Store for free, direct link is here.

Android - Smart Voice Recorder, by SmartMob.

As with the iOS option, this comes with a dropbox export option for your to easily transfer your audio files from your device to the pupil. This app is free on Google Play and its direct link is here.


Propan-2-ol Woosh Bottle (120fps)

1 min read

When doing the woosh bottle, sometimes Ethanol can burn through too quickly. An impressive woosh but what if you select a slower burning alcohol? 

The above video was filmed on an iPhone 5S and processed using iMovie. The slower burn lets you see the ignition of the vapour through the bottle more clearly, and even without slowing the video, it is impressive.


Hydrogen/Air Mixture @ 1atm

1 min read

Extracted hydrogen from salt water over the course of an afternoon, this was the result.