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- Since 1889, a kilogram was the mass of a shiny piece of platinum-iridium alloy kept in a special glass case at the International Bureau of weights and measures.
- Since 1889, a kilogram was the mass of a shiny piece of platinum-iridium alloy kept in a special glass case at the International Bureau of weights and measures.
- This definition of mass has been modified on 20th May 2019, the reason being that the carefully kept platinumiridium piece is seen to pick up micro particles of dirt and is also affected by the atmosphere causing its mass to change.
- This definition of mass has been modified on 20th May 2019, the reason being that the carefully kept platinumiridium piece is seen to pick up micro particles of dirt and is also affected by the atmosphere causing its mass to change.
- The new measure of kilogram is defined in terms of magnitude of electric current.
- The new measure of kilogram is defined in terms of magnitude of electric current.
- We know that electric current can be used to make an electromagnet.
- We know that electric current can be used to make an electromagnet.
- An electromagnet attracts magnetic materials and is thus used in research and in industrial applications such as cranes to lift heavy pieces of iron/steel.
- An electromagnet attracts magnetic materials and is thus used in research and in industrial applications such as cranes to lift heavy pieces of iron/steel.
- Thus the kilogram mass can be described in terms of the amount of current which has to be passed through an electromagnet so that it can pull down one side of an extremely sensitive balance to balance the other side which holds one standard kg mass.
- Thus the kilogram mass can be described in terms of the amount of current which has to be passed through an electromagnet so that it can pull down one side of an extremely sensitive balance to balance the other side which holds one standard kg mass.
- While dealing with mass of atoms and molecules, kg is an inconvenient unit.
- While dealing with mass of atoms and molecules, kg is an inconvenient unit.
- Therefore, their mass is measured in atomic mass unit.
- Therefore, their mass is measured in atomic mass unit.
- It will be easy to compare mass of any atom in terms of mass of some standard atom which has been decided internationally to be C12 atom.
- It will be easy to compare mass of any atom in terms of mass of some standard atom which has been decided internationally to be C12 atom.
- The (1/12)th mass of an unexcited atom of C12 is called atomic mass unit (amu).
- The (1/12)th mass of an unexcited atom of C12 is called atomic mass unit (amu).
- 1 amu = 1.6605402Í X 10^-27 kg with an uncertainty of 10 in the last two decimal places.
- 1 amu = 1.6605402Í X 10^-27 kg with an uncertainty of 10 in the last two decimal places.
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