WANT to measure a fundamental constant in the comfort of your own home? Grab a pile of Lego and get building. Just in time for Christmas, researchers at the US National Institute of Standards and Technology (NIST) have provided instructions for a Lego watt balance, which can fix the official value of the kilogram.
At the moment the kilogram is defined in relation to a lump of metal in a basement in Paris – not the most reliable measure. One way to improve this is to define it in terms of the fundamental constants. This can be done using a watt balance, which measures weight in terms of voltage and current, which depend on the Planck constant.
Xiang Zhang and his colleagues say their $650 Lego version can make this measurement with an uncertainty of 1 per cent – not as good as ultra-precise watt balances with an uncertainty of 1 in 100 million, but much cheaper.
The Lego device looks a bit like a traditional set of scales, with weighing pans on either side. It's not totally made from plastic blocks, though – you also need coils of wire beneath the pan and strong neodymium magnets nearby to make a measurement (http://ift.tt/1ylawVv).
Finding the mass requires two measurements. First place a weight on one of the pans, moving the coil past the magnet and inducing a voltage. Then run a current through the coil, creating an electromagnetic force on the pan that counteracts the weight. Comparing these two gives you the weight's mass, which can be compared to the Planck constant.
This article appeared in print under the headline "DIY device to define the kilogram – using Lego"
- Subscribe to New Scientist and you'll get:
- New Scientist magazine delivered every week
- Unlimited access to all New Scientist online content -
a benefit only available to subscribers - Great savings from the normal price
- Subscribe now!
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
