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Question
Calculate the solid angle subtended by the periphery of an area of 1 cm2 at a point situated symmetrically at a distance of 5 cm from the area.
Solution
Solid angle, Ω = `"Area"/("Radial distance")^2`
= `(1 cm^2)/(5 cm)^2`
= `1/25`
= 4 × 10–2 steradian ......(∵ Area = 1 cm2, distance = 5 cm)
Important point: Please keep in mind that a solid angle is for 3-D figures like spheres, cones etc and a plane angle is for plane objects or 2-D figures like circles, arcs etc.
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