Question

A point source is kept at centre of a sphere. The intensity of light at point \(A\) is \(I\). Find intensity at point \(B\).

• A. \(I/2\)
• B. \(2I\)
• C. \(I\)
• D. \(I/3\)

Answer 1

The Correct Option is C

Concept: Intensity of light from a point source is given by \[ I=\frac{P}{4\pi r^2} \] where \(r\) is the distance from the source. Step 1: Analyze distances.} Points \(A\) and \(B\) lie on the same spherical surface. Thus distance from the source to both points is the same: \[ r_A=r_B \]
Step 2: Apply inverse square law.} \[ I=\frac{P}{4\pi r^2} \] Since \(r\) is same for both points, \[ I_A=I_B \] Final Result \[ I_B=I \]