Question

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. $\left( \frac{5}{4} \right)^{\frac{3}{2}}$
• C. $\frac{4}{3}$
• D. $\frac{4}{5}$

Answer 1

Answer: (B)

$\left( \frac{5}{4} \right)^{\frac{3}{2}}$

Answer 2

$\frac{I_{centre}}{I_{edge}} = \frac{(r^{2} + h^{2})^{3/2}}{h^{3}} = \frac{\left( 1 + \frac{1}{4} \right)^{3/2}}{1^{3}} = \left( \frac{5}{4} \right)^{3/2}$