How Is the Solid Angle for a Circular Detector Calculated?

[MickieDBaca]

1. The solid angle subtended by a 100 cm^2 circular detector at a distance of 1 m is ______steradians.

2. Ω = A/r^2 and A =∏r^2 (area of a circle)

3. I originally tried to find r by solving 100 = ∏r^2 and I got r = 5.6. I then tried to plug into the first equation for Ω only to realize that really, I had just gone in a circle and ended up with 4∏, which is the measure of sphere in steradians. Then I tried the tangent (5.6/100) to find the angle in degrees... The answer is .01 but I am unsure why...

 

[vela]

You need to keep in mind what the various quantities appearing in the formulas mean. Try again paying a bit more attention to which values go where.