# Solid Angle

by Hoofbeat
Tags: angle, solid
 Sci Advisor HW Helper P: 11,928 A transversal section through a cone,if done as to contain the axis reveals a triangle.My gues is that in your case,the triangle is isosceles...The 2 rightangle triangle (congruent) each has an angle $\alpha$...So the total angle is $2\alpha$...Use the definition of the solid angle and compute it. Daniel.
 Sci Advisor P: 1,477 A 2D angle in radians is given by s/r (Where s is the arc length subtended by the angle). Solid Angles are the 3D equivalent and have (dimensionless) units of steraidians. The Solid Angle is the area projected by the solid angle on a sphere of radius r, divided by r squared. $$SA=A/r^2$$ The Solid Angle of an isotropic source, for example would therefore be $$4\pi r^2/r^2 = 4\pi$$ and a hemisphere would be $$2\pi$$ and so on... Claude.