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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.

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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.

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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.

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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](http://twitter.com/LeeJSummers).