Question

1: How many radians account for circumference of a circle ?
2: How many steradians account for circumference of a sphere?

Answer 1

Explanation:

1: So the circumference of a circle is 2 PI larger than its radius. This means that in any circle, there are 2 PI radians. Therefore 360º = 2 PI radians.

2: A sphere subtends 4 pi square radians (steradians) about the origin. By analogy, a circle subtends 2 pi radians about the origin.