**Question 9:** Are radian and Steradian basic units of SI? Justify your answer.

Answer

Radian and steradian are not the base units of SI.

### Definitions of radian and steradian

- Radian is the plane angle subtended at the center of a circle by an arc equal to the length of the radius of the same circle.
- Steradian is the solid angle subtended at the center of sphere by an area equal to the square of the radius of the same sphere.

Both of them are the units of purely geometrical quantities.

In 1960, the general conference on weights and measures, had not classified both units as base units of SI. These are called supplementary units.

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