Question

DEFINE(i) RADIAN(ii) STERADIAN

Answer 1

(i) Radian :
It is a unit of a angle in a angle in a plane.
1 radian is the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.
$d\theta =\frac{ds}{r}radian$

(ii) Steradian :
It is a unit of solid angle.
One steradian is the solid angle subtended at the centre of a sphere by the surface of the sphere, which is equal in area to the square of radius of the sphere.
$d\Omega =\frac{dA}{r^2}steradian$