Civil Engineering - SI Units - Discussion
Discussion Forum : SI Units - Section 1 (Q.No. 25)
25.
The bar used for defining the standard metre at the International office of weights and measures at Sevres near Paris, is composed of
Discussion:
2 comments Page 1 of 1.
Kureshi sajid said:
8 years ago
Why 10% of iridium? Please explain.
Mervin said:
3 years ago
The International Prototype Kilogram stored in a vault in Paris, was replaced by a formula using Planck's constant in 2019. The IPK was losing mass so the metrology community redefined the kilogram with the aid of the Planck constant.
The IPK is a roughly golf-ball-sized object made of a platinum alloy known as "Pt/'10Ir", which is 90% platinum and 10% iridium (by mass) and is machined into a right-circular cylinder with a height equal to its diameter of about 39 millimeters to reduce its surface area.
The IPK is a roughly golf-ball-sized object made of a platinum alloy known as "Pt/'10Ir", which is 90% platinum and 10% iridium (by mass) and is machined into a right-circular cylinder with a height equal to its diameter of about 39 millimeters to reduce its surface area.
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