A point light source emits E.M. waves in free space. A detector, placed at a distance of $L$ m, measures the intensity as $I_0$. The detector is now shifted to another location on the same spherical surface ensuring the angle between original location and new location as $45^\circ$. The measured intensity at new location will be ______.
Answer: (B) $I_0$
Concept. A point source radiates equally in all directions, so the intensity $I=\dfrac{P}{4\pi r^2}$ depends only on the distance $r$ from the source.
Step 1. Distance at the new position. The detector stays on the same sphere, so $r=L$ again; the $45^\circ$ angle does not change $r$.
Step 2. Intensity. Same $r$, same intensity: $I_0$.
Answer. $I_0$ (Option B).
Solution by Sreeraj P, M.Sc Physics
