DIY: How to measure Planck’s constant using LEGO
The kilogram is about to be redefined using Planck’s constant and you can now measure this constant yourself with a little ‘do-it-yourself’ effort and some LEGO.
32 | LAB+LIFE SCIENTIST - March 2015
T
he International System of Units (Le
of measurements improves. The meter was first
Système International d’Unités or SI units) is based on
defined as 1/10 000 000 of the meridian through
seven building blocks which can measure length, mass,
Paris between the North Pole and the equator but
time, electric current, thermodynamic temperature,
the first prototype was short by 0.2 mm because
amount of substance and luminous intensity - or in
researchers miscalculated the flattening of the earth
other words, the metre, kilogram, second, ampere,
due to its rotation. Still this length became the
kelvin, mole and candela. All other ‘coherent SI
standard. In 1889, a new international prototype
units’ can be derived from these base units plus a set
was made of an alloy of platinum with 10% iridium,
of decimal-based multipliers.
to within 0.0001, that was to be measured at the
In the olden days, artefacts were used to define
melting point of ice. In 1927, the meter was more
the root units. However, over time, these unit
precisely defined as the distance, at 0°, between
definitions have been modified as the technology
the axes of the two central lines marked on the
of measurement progresses and the precision
bar of platinum-iridium. This bar being subject to
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