Le Grand K — a platinum ingot housed in Paris according to whose weight the kilogram is defined — is all set for retirement. Scientists are expected to vote to replace it with an electric current at the General Conference on Weights and Measures, which will conclude in Paris on Friday.
Le Grand K has set the standard of the international system of measuring weights since 1889. However, its weight has changed over the years due to deterioration. The fluctuation itself is said to amount to the weight of a human eyelash. This may not seem like much, but there are several fields in which such a tiny change could be consequential, such as nanoengineering and pharmaceuticals. This is why those responsible for managing the metric system wish to define the kilogram through a new standard.
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“We know from comparing the kilogram in Paris with all the copies of the kilogram around the world that there are discrepancies between them and Le Grand K,” said Dr Stuart Davidson of the National Physical Laboratory in London. “This is not acceptable from a scientific point of view. So even though Le Grand K is fit for the purpose at the moment, it won’t be in 100 years time.”
The kilogram will now be defined using the pull of an electromagnet, which is directly dependent on the amount of current passed through its coils. As such, there is a direct relationship between electricity and weight. In principle, scientists can define a kilogram, or any other amount of weight, in terms of the amount of electricity needed to counteract its force.
The accuracy of this new kilogram will be measured using a Kibble balance, a super accurate set of scales. One side will be pulled down by an electromagnet, while the other side has a weight amounting to one kilogram on it. The amount of electrical current equivalent to one kilogram will be determined when both scales are level with each other.