Q. A lamp is hanging $1\ m$ above the centre of a circular table of diameter $1m$. The ratio of illuminaces at the centre and the edge is
A) $\frac{1}{2}$
B) $\left( \frac{5}{3} \right)^{\frac{3}{2}}$
C) $\frac{4}{3}$
D) $\frac{4}{5}$
Explanation
(b) $\frac{I_{centre}}{I_{edge}} = \frac{\left( r^{2} + h^{2} \right)^{3/2}}{h^{3}} = \frac{\left( 1 + \frac{1}{4} \right)^{3/2}}{1^{3}} = \left( \frac{5}{4} \right)^{3/2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.