Concepts Of Physics MCQ Edition [Volume 1]PhysicsPhotometry
The figure displays a glowing mercury tube. The intensities at points A , B , and C are related by
Options
- AB > C > A
- BB = C > A
- CA > C > B
- DB = C < A
Correct answer
D. B = C < A
Step-by-step solution
The glowing mercury tube acts as a finite line source of light. The intensity of light at a given point depends on its distance from the source elements and the angle at which the light rays arrive. The illuminance is given by E = dI r^2 . Point A is located on the perpendicular bisector of the tube. For this point, the average distance r to the various elements of the tube is minimum, and the light rays strike most directly ( is maximum). Hence, the intensity is maximum at A. Points B and C are symmetrically place